Why are surge arresters not allowed?

I am brand new to these boards but not to cruising. I have a question about the use of surge arresters.

I would really appreciate someone explaining in detail exactly why electrical distribution strips containing surge arresters are not allowed on cruise ships. I’m certain there must be a valid reason but I simply have not heard it.

It seems as though strips with no surge arresters are OK but those with them are not OK.

I have some training in electronics and have seen a number of “explanations” of the reason, but none of them seem to actually answer the question. I see numerous statements which seem to me to be either generalizations, simply incorrect or examples of electrical problems that were not actually caused by a surge arrester.

I understand that having a surge arrester may not solve certain types of problems, but I’d really like someone to explain why having a surge arrester is worse than not having one on a similar distribution strip.

Thanks a lot for any information you may have to help me out.

Tex

I am brand new to these boards but not to cruising. I have a question about the use of surge arresters.

 

 

 

I would really appreciate someone explaining in detail exactly why electrical distribution strips containing surge arresters are not allowed on cruise ships. I’m certain there must be a valid reason but I simply have not heard it.

 

 

 

It seems as though strips with no surge arresters are OK but those with them are not OK.

 

 

 

I have some training in electronics and have seen a number of “explanations” of the reason, but none of them seem to actually answer the question. I see numerous statements which seem to me to be either generalizations, simply incorrect or examples of electrical problems that were not actually caused by a surge arrester.

 

 

 

I understand that having a surge arrester may not solve certain types of problems, but I’d really like someone to explain why having a surge arrester is worse than not having one on a similar distribution strip.

 

 

 

Thanks a lot for any information you may have to help me out.

 

 

 

Tex

I seem to remember this question being asked and answered previously on CC. Not sure but I think the issue is related to "mistakenly" plugging the 120v surge suppressor into the 240v (using only an adaptor plug for the connection). If I remember correctly, that may flip the breaker for your and multiple other cabins. However, don't quote me on that.

I am brand new to these boards but not to cruising. I have a question about the use of surge arresters.

 

I would really appreciate someone explaining in detail exactly why electrical distribution strips containing surge arresters are not allowed on cruise ships. I’m certain there must be a valid reason but I simply have not heard it.

 

It seems as though strips with no surge arresters are OK but those with them are not OK.

 

I have some training in electronics and have seen a number of “explanations” of the reason, but none of them seem to actually answer the question. I see numerous statements which seem to me to be either generalizations, simply incorrect or examples of electrical problems that were not actually caused by a surge arrester.

 

I understand that having a surge arrester may not solve certain types of problems, but I’d really like someone to explain why having a surge arrester is worse than not having one on a similar distribution strip.

 

Thanks a lot for any information you may have to help me out.

 

Tex

If you search my posting history, you'll see my many forays into explaining why these are not allowed, maybe you've seen some in your search. The long and short of it can be explained by the USCG Safety Notice here:

http://www.uscg.mil/tvncoe/Documents/safetyalerts/SurgeProtectiveDevices.pdf

yep

on one of my ships, had a surge protector which was installed without asking burst into flames one afternoon

has to do with the difference in wiring due to the way the ground must be handled in the ship environment

in the early days of using PC's on ships, small UPS systems were found to have a similar tendency to burst into flames ....

kind of a bummer . . .

we had a list of 'approved' items. but sadly some saw one installed and assumed they were all the same ...

yep

 

on one of my ships, had a surge protector which was installed without asking burst into flames one afternoon

 

has to do with the difference in wiring due to the way the ground must be handled in the ship environment

 

in the early days of using PC's on ships, small UPS systems were found to have a similar tendency to burst into flames ....

 

kind of a bummer . . .

 

we had a list of 'approved' items. but sadly some saw one installed and assumed they were all the same ...

We had the same problems over the years with UPS systems, because they would look for the 120v between hot and ground in order to know that "normal" power was available. If you plugged in a shoreside US UPS, it would immediately switch to battery. We have found that marine suppliers, and now with nearly all ships going to 220v power, european UPS systems, we no longer have these problems.

yea ... I am talking about early to mid 80's when PCs on ships was in its infancy ... but I have surge protectors at home that are that old too!

the one that actually burned for me was in 2001 . . .

what I'm saying is: it is a valid concern not just some made up stuff . .

as a spin off - one can be a very very good electrician and be unqualified to work in a marine environment .... there are differences.

yea ... I am talking about early to mid 80's when PCs on ships was in its infancy ... but I have surge protectors at home that are that old too!

 

the one that actually burned for me was in 2001 . . .

 

what I'm saying is: it is a valid concern not just some made up stuff . .

 

as a spin off - one can be a very very good electrician and be unqualified to work in a marine environment .... there are differences.

The hardest argument I get here on CC is that the USCG Safety Notice "applies to cargo ships, and cruise ships are different". Ah, well, the crusade goes on. Forward, Sancho.

Thanks for having our back, as always, ex-Coastie.

If you search my posting history, you'll see my many forays into explaining why these are not allowed, maybe you've seen some in your search. The long and short of it can be explained by the USCG Safety Notice here:

 

http://www.uscg.mil/tvncoe/Documents/safetyalerts/SurgeProtectiveDevices.pdf

Hi chengkp75,

Thanks for your reply to my query but I’m afraid that I still do not know the answer to my question.

Coast Guard communication 03-13b that you reference, is typical of several discussions on the subject in that it seems to only state that SPDs (surge protection devices) are bad and may cause fires, but it doesn’t explain how they might do this.

This is an excerpt and the only problem highlighted in the Coast Guard Communication.

<<A marine casualty investigation of two separate stateroom fires onboard a U.S. Flag Container ship revealed that the sources of the fires were attributed to the use of SPDs plugged into a lighting circuit. It was discovered that a ground had developed on another circuit that was connected to the same distribution panel providing power to the staterooms. This ground created an imbalance of voltage between the two power conductors supplying the SPDs which caused excessive currents, overheating, and subsequently, a fire. In this instance, even if the SPDs automatically tripped as designed, only one power conductor would have been secured while the other would continue to provide power, possibly shorting to the device’s ground wire and the structure of the vessel.>>

I do not understand how the problem that is given as the example, was caused by an SPD. It appears to have had little to do with a SPD. The communication only says that the SPD might not have solved the problem. Am I missing something here?

Of course I also don’t understand the meaning of << This ground created an imbalance of voltage between the two power conductors supplying the SPDs which caused excessive currents, overheating, and subsequently, a fire.>> Could you possibly translate these words into something that defines clearly the circuit operation for the example being given?

Unfortunately as I have said in my previous posting, to me this does not explain why having a SPD in an electrical distribution strip is unacceptable while a similar distribution strip without any protection whatever, is acceptable.

Thanks for your help.

Tex

Let’s try, having some difficulty with my browser today, so this is my third attempt to complete this, so thought I’d compose it offline.

Let’s first deal with the ground. Shipboard power systems want to know if any current is flowing to ground, as this can cause galvanic corrosion in the ship. Therefore, unlike shore power, a ship needs to know if power is flowing between either leg of the power system to ground. With your typical shore power system (home wiring), there is a “neutral” leg that is maintained at ground potential by connecting it to the ground in the breaker panel. Therefore, the only way to detect current flowing to ground in the “neutral” leg is with a ground fault device, which measures the current in the hot and neutral legs, and trips when there is any difference, since that difference means it is flowing in the ground connector. Ships use a “ground detection system”, since both power legs are at a different potential from the ground. At the distribution panel, there is a resistor and ammeter connected between each power leg and ground. If there are no accidental grounds in the ship, this ground detection connection is an incomplete circuit, and the ammeter reads zero. When something fails to ground, this completes the circuit, and the ammeter reads current. The resistor limits the amount of current allowed to flow from one ground fault. However, if two devices fail to ground, the ammeter will still measure current through itself, but between the two grounded devices there can be unlimited current, depending on the severity of the fault, up to the circuit breaker limit. This high current may or may not be seen by either of the grounded devices, depending on where the ground occurs, it may just be in the wiring, but the current will cause heat. The flow of current to ground will drop the voltage between the grounded power leg and ground, thereby creating a voltage variation between the two power legs.

Now let’s move to the SPD. This device looks at the voltage between what it considers the hot and neutral legs, to determine if there is a voltage spike, since the neutral is at ground potential. From the above regarding grounds, this is not an accurate way to measure voltage spikes on ships, as the “hot” or power leg that does not have an accidental ground, may not be above the clamping voltage of the SPD, but with a lower “neutral” or accidentally grounded leg at a different potential than normal, it will see a higher voltage difference, and will start to shunt voltage from the “hot” to the “neutral”. This action by the SPD generates heat as a normal byproduct, but the unit is designed to handle this for short periods. Because a shipboard ground may be present for hours or days before it is tracked down and repaired, the SPD can be shunting power this whole time, generating heat. It also adds current to the “neutral” or grounded leg, which then flows to ground, adding to the current flowing in the ground fault, causing more heat. Now, once the joule rating of the SPD is reached (the total amount of power it can handle, not the instantaneous spike power), the circuitry fails, the SPD shorts to “neutral”, and the circuit breaker in the power strip opens the “hot” leg. However, if at this time, the power strip has failed to ground, the “neutral” leg which is still connected, can short circuit to the ground connection, and continue the current and heat.

Not sure if this clears it up for you or not. I’ll end by saying that any device, whether an SPD or as mentioned above a UPS, that assumes there is a “neutral” leg at zero volts to ground, will not work as designed when placed in a shipboard electrical system.

I seem to remember this question being asked and answered previously on CC. Not sure but I think the issue is related to "mistakenly" plugging the 120v surge suppressor into the 240v (using only an adaptor plug for the connection). If I remember correctly, that may flip the breaker for your and multiple other cabins. However, don't quote me on that.

I plugged a 110V surge suppressed power strip into an outlet in a B&B in England. Smoke came out of the thing and half the circuit breakers in the place tripped. I told the owner at breakfast about it and apologized. She did not believe it so she tried it in her kitchen. The entire kitchen tripped off.

No damage to the B&B wiring but my power strip was toast.

DON

Let’s try, having some difficulty with my browser today, so this is my third attempt to complete this, so thought I’d compose it offline.

 

Let’s first deal with the ground. Shipboard power systems want to know if any current is flowing to ground, as this can cause galvanic corrosion in the ship. Therefore, unlike shore power, a ship needs to know if power is flowing between either leg of the power system to ground. With your typical shore power system (home wiring), there is a “neutral” leg that is maintained at ground potential by connecting it to the ground in the breaker panel. Therefore, the only way to detect current flowing to ground in the “neutral” leg is with a ground fault device, which measures the current in the hot and neutral legs, and trips when there is any difference, since that difference means it is flowing in the ground connector. Ships use a “ground detection system”, since both power legs are at a different potential from the ground. At the distribution panel, there is a resistor and ammeter connected between each power leg and ground. If there are no accidental grounds in the ship, this ground detection connection is an incomplete circuit, and the ammeter reads zero. When something fails to ground, this completes the circuit, and the ammeter reads current. The resistor limits the amount of current allowed to flow from one ground fault. However, if two devices fail to ground, the ammeter will still measure current through itself, but between the two grounded devices there can be unlimited current, depending on the severity of the fault, up to the circuit breaker limit. This high current may or may not be seen by either of the grounded devices, depending on where the ground occurs, it may just be in the wiring, but the current will cause heat. The flow of current to ground will drop the voltage between the grounded power leg and ground, thereby creating a voltage variation between the two power legs.

 

Now let’s move to the SPD. This device looks at the voltage between what it considers the hot and neutral legs, to determine if there is a voltage spike, since the neutral is at ground potential. From the above regarding grounds, this is not an accurate way to measure voltage spikes on ships, as the “hot” or power leg that does not have an accidental ground, may not be above the clamping voltage of the SPD, but with a lower “neutral” or accidentally grounded leg at a different potential than normal, it will see a higher voltage difference, and will start to shunt voltage from the “hot” to the “neutral”. This action by the SPD generates heat as a normal byproduct, but the unit is designed to handle this for short periods. Because a shipboard ground may be present for hours or days before it is tracked down and repaired, the SPD can be shunting power this whole time, generating heat. It also adds current to the “neutral” or grounded leg, which then flows to ground, adding to the current flowing in the ground fault, causing more heat. Now, once the joule rating of the SPD is reached (the total amount of power it can handle, not the instantaneous spike power), the circuitry fails, the SPD shorts to “neutral”, and the circuit breaker in the power strip opens the “hot” leg. However, if at this time, the power strip has failed to ground, the “neutral” leg which is still connected, can short circuit to the ground connection, and continue the current and heat.

 

Not sure if this clears it up for you or not. I’ll end by saying that any device, whether an SPD or as mentioned above a UPS, that assumes there is a “neutral” leg at zero volts to ground, will not work as designed when placed in a shipboard electrical system.

Hi chengkp75,

Thanks a bunch for the explanation. I really do appreciate your taking the time to write it. I would like to discuss it in detail.

First, let’s agree on some terms that will make the discussion clearer. I assume you are speaking of a ship’s electrical distribution system where the two power leads each have a 60 VAC potential from the “Neutral” lead, just with 180 degree reversed phase timing in each leg, so when considering just the power leads themselves, the voltage between them adds up to 120 VAC. This “Neutral” lead is connected back to a point on the ship’s electrical generator but not connected to the ship’s hull. Is my assumption of the configuration correct?

If so, this is basically the same as a standard home wiring system, except for the house system, the voltages would be “plus and minus” 120 VAC, adding to the standard 240 VAC house supply. Also, lets only use the term “Ground” to mean the hull of the ship as opposed to the “Neutral” wire which is electrically in between the two power leads. I understand that in home wiring, the “Neutral” is connected to “Ground” (a rod driven into the earth near the house from which we get the term “Ground” connection) at the circuit breaker panel. But in shipboard systems, the “Neutral” is not connected directly to “Ground” (the ship’s hull.)

Now you speak of an inadvertent connection of <<something fails to ground…>> I need to assume here you are speaking of either a power lead or the “Neutral” lead somehow shorting to “Ground” (the ship’s hull.) I agree that in either case, at least one of the ammeters you mention, connected from the power leads to “Ground” (the ship’s hull) would show some current flowing which, as you stated, would be limited by the resistor in series with that ammeter.

Next you speak of << two devices fail to ground…>> Here I must assume you mean either two different power leads each shorting to “Ground” (the ship’s hull) or one power lead and the “Neutral” lead both shorting to “Ground” (the ship’s hull.) If either of these events occurs, than potentially large currents can flow between the two leads in question with the ship’s hull acting as the short circuit connection. Heat and fire are certainly distinct possibilities in this situation and the problem must be corrected quickly. This situation will, in general, trip the circuit breakers built into the ship’s electrical distribution system.

But so far, nothing we have said has anything to do with SPDs.

Now when speaking of a SPD in use, you say << the “hot” or power leg that does not have an accidental ground, may not be above the clamping voltage of the SPD. >> This will be true in general as the clamping voltage of standard SPDs is in the 300 to 500 volt range so of course, a short circuit type fault in a 120 VAC system is not going to cause the SPD to shunt current continually around the fault.

You then continue << but with a lower “neutral” or accidentally grounded leg at a different potential than normal, it will see a higher voltage difference, and will start to shunt voltage from the “hot” to the “neutral”.>>.

I do not understand this statement. With a “plus or minus” 60 VAC ship’s electrical distribution system (adding up to a 120 VAC system,) it would seem that even with an extreme variation of the voltage on either of the power leads (even if the voltage on the power lead shorted to “Ground” (the ship’s hull) goes down to near zero,) the voltage across the SPD cannot exceed the 120VAC of the distribution system. There simply isn’t any higher sustained voltage in the system

Now standard SPDs are made to use continually with 120 VAC systems. So even with the <<higher voltage difference>>, I don’t understand why the SPD would << start to shunt voltage from the “hot” to the “neutral”.>>. The voltage across the SPD in this case would seem to be no greater than 120 VAC, which is well within the normal everyday operating voltage of any standard SPD. And I don’t believe that they pass any significant current at 120 VAC or << …generate heat as a normal byproduct. >> at this voltage. So I don’t understand why they would be subject to a severe temperature rises or failure.

I hope I have explained my question clearly. I really appreciate your helping me understand the situation. As I have stated previously, I still don’t understand why having a SPD in an electrical distribution strip is unacceptable while a similar distribution strip without any protection whatever, is acceptable.

Tex

Hi chengkp75,

 

Thanks a bunch for the explanation. I really do appreciate your taking the time to write it. I would like to discuss it in detail.

 

First, let’s agree on some terms that will make the discussion clearer. I assume you are speaking of a ship’s electrical distribution system where the two power leads each have a 60 VAC potential from the “Neutral” lead, just with 180 degree reversed phase timing in each leg, so when considering just the power leads themselves, the voltage between them adds up to 120 VAC. This “Neutral” lead is connected back to a point on the ship’s electrical generator but not connected to the ship’s hull. Is my assumption of the configuration correct?

 

If so, this is basically the same as a standard home wiring system, except for the house system, the voltages would be “plus and minus” 120 VAC, adding to the standard 240 VAC house supply. Also, lets only use the term “Ground” to mean the hull of the ship as opposed to the “Neutral” wire which is electrically in between the two power leads. I understand that in home wiring, the “Neutral” is connected to “Ground” (a rod driven into the earth near the house from which we get the term “Ground” connection) at the circuit breaker panel. But in shipboard systems, the “Neutral” is not connected directly to “Ground” (the ship’s hull.)

 

Now you speak of an inadvertent connection of <<something fails to ground…>> I need to assume here you are speaking of either a power lead or the “Neutral” lead somehow shorting to “Ground” (the ship’s hull.) I agree that in either case, at least one of the ammeters you mention, connected from the power leads to “Ground” (the ship’s hull) would show some current flowing which, as you stated, would be limited by the resistor in series with that ammeter.

 

Next you speak of << two devices fail to ground…>> Here I must assume you mean either two different power leads each shorting to “Ground” (the ship’s hull) or one power lead and the “Neutral” lead both shorting to “Ground” (the ship’s hull.) If either of these events occurs, than potentially large currents can flow between the two leads in question with the ship’s hull acting as the short circuit connection. Heat and fire are certainly distinct possibilities in this situation and the problem must be corrected quickly. This situation will, in general, trip the circuit breakers built into the ship’s electrical distribution system.

 

But so far, nothing we have said has anything to do with SPDs.

 

Now when speaking of a SPD in use, you say << the “hot” or power leg that does not have an accidental ground, may not be above the clamping voltage of the SPD. >> This will be true in general as the clamping voltage of standard SPDs is in the 300 to 500 volt range so of course, a short circuit type fault in a 120 VAC system is not going to cause the SPD to shunt current continually around the fault.

 

You then continue << but with a lower “neutral” or accidentally grounded leg at a different potential than normal, it will see a higher voltage difference, and will start to shunt voltage from the “hot” to the “neutral”.>>.

 

I do not understand this statement. With a “plus or minus” 60 VAC ship’s electrical distribution system (adding up to a 120 VAC system,) it would seem that even with an extreme variation of the voltage on either of the power leads (even if the voltage on the power lead shorted to “Ground” (the ship’s hull) goes down to near zero,) the voltage across the SPD cannot exceed the 120VAC of the distribution system. There simply isn’t any higher sustained voltage in the system

 

Now standard SPDs are made to use continually with 120 VAC systems. So even with the <<higher voltage difference>>, I don’t understand why the SPD would << start to shunt voltage from the “hot” to the “neutral”.>>. The voltage across the SPD in this case would seem to be no greater than 120 VAC, which is well within the normal everyday operating voltage of any standard SPD. And I don’t believe that they pass any significant current at 120 VAC or << …generate heat as a normal byproduct. >> at this voltage. So I don’t understand why they would be subject to a severe temperature rises or failure.

 

I hope I have explained my question clearly. I really appreciate your helping me understand the situation. As I have stated previously, I still don’t understand why having a SPD in an electrical distribution strip is unacceptable while a similar distribution strip without any protection whatever, is acceptable.

 

Tex

Not sure I have the ability to explain further, its been 4 decades since I took classes in electrical theory (some quickie refreshers, but nothing in full detail), so you probably have an advantage over me.

Anyway, one point I didn't mention is that ships power is 3-phase down to where it is distributed to the outlets, so between two circuits, there is not necessarily a cut and dried 180 degree phase shift.

Now that I think about it, and correct me if I'm wrong, because semi-conductor theory is not my strong point, an SPD built for shore use looks for voltages between the hot leg and ground (using shore terminology), and this voltage alternates between 120 and 0. On a shipboard system, the voltage between the hot leg and ground alternates from +60 to -60. When the voltage is -60 on the hot leg, the neutral leg is at +60, and you have reversed the polarity of the voltage the semi-conductors see. This is what causes the overheating (reversing the polarity of voltage applied to the semi-conductor) which is aggravated when an out of phase ground is introduced.

Other than this, I'm out of ways to explain a phenomenon I know happens.

This is hard to discuss without a schematic. But I think I get the gist of it. It all comes down to one sentence in the Coast Guard warning: "For shipboard applications, it is important that protectors interrupt both power leads". On shore, it is okay, even desirable, to allow current from " ground" to neutral. But on ship, the two leads are not so much VCC and GND, but more like V+ and V-. Current between V- and GND is not desired, and so a floating potential exists between those two nodes. If the surge protector interrupts only V+, you create a short between V- and GND; which on shore they should be equipotential anyway. On ship, you trip a breaker or worse. A "certified" surge protector would probably have a second relay switching V-. Some do have that, some don't. Personally I don't see why not all just do. I guess it is somehow better to bleed excess current "harmlessly" to ground, as a lightning rod does, rather than simply optoisolate your valuable device completely.

Hi chengkp75,

 

Thanks a bunch for the explanation. I really do appreciate your taking the time to write it. I would like to discuss it in detail.

 

First, let’s agree on some terms that will make the discussion clearer. I assume you are speaking of a ship’s electrical distribution system where the two power leads each have a 60 VAC potential from the “Neutral” lead, just with 180 degree reversed phase timing in each leg, so when considering just the power leads themselves, the voltage between them adds up to 120 VAC. This “Neutral” lead is connected back to a point on the ship’s electrical generator but not connected to the ship’s hull. Is my assumption of the configuration correct?

 

If so, this is basically the same as a standard home wiring system, except for the house system, the voltages would be “plus and minus” 120 VAC, adding to the standard 240 VAC house supply. Also, lets only use the term “Ground” to mean the hull of the ship as opposed to the “Neutral” wire which is electrically in between the two power leads. I understand that in home wiring, the “Neutral” is connected to “Ground” (a rod driven into the earth near the house from which we get the term “Ground” connection) at the circuit breaker panel. But in shipboard systems, the “Neutral” is not connected directly to “Ground” (the ship’s hull.)

 

Now you speak of an inadvertent connection of <<something fails to ground…>> I need to assume here you are speaking of either a power lead or the “Neutral” lead somehow shorting to “Ground” (the ship’s hull.) I agree that in either case, at least one of the ammeters you mention, connected from the power leads to “Ground” (the ship’s hull) would show some current flowing which, as you stated, would be limited by the resistor in series with that ammeter.

 

Next you speak of << two devices fail to ground…>> Here I must assume you mean either two different power leads each shorting to “Ground” (the ship’s hull) or one power lead and the “Neutral” lead both shorting to “Ground” (the ship’s hull.) If either of these events occurs, than potentially large currents can flow between the two leads in question with the ship’s hull acting as the short circuit connection. Heat and fire are certainly distinct possibilities in this situation and the problem must be corrected quickly. This situation will, in general, trip the circuit breakers built into the ship’s electrical distribution system.

 

But so far, nothing we have said has anything to do with SPDs.

 

Now when speaking of a SPD in use, you say << the “hot” or power leg that does not have an accidental ground, may not be above the clamping voltage of the SPD. >> This will be true in general as the clamping voltage of standard SPDs is in the 300 to 500 volt range so of course, a short circuit type fault in a 120 VAC system is not going to cause the SPD to shunt current continually around the fault.

 

You then continue << but with a lower “neutral” or accidentally grounded leg at a different potential than normal, it will see a higher voltage difference, and will start to shunt voltage from the “hot” to the “neutral”.>>.

 

I do not understand this statement. With a “plus or minus” 60 VAC ship’s electrical distribution system (adding up to a 120 VAC system,) it would seem that even with an extreme variation of the voltage on either of the power leads (even if the voltage on the power lead shorted to “Ground” (the ship’s hull) goes down to near zero,) the voltage across the SPD cannot exceed the 120VAC of the distribution system. There simply isn’t any higher sustained voltage in the system

 

Now standard SPDs are made to use continually with 120 VAC systems. So even with the <<higher voltage difference>>, I don’t understand why the SPD would << start to shunt voltage from the “hot” to the “neutral”.>>. The voltage across the SPD in this case would seem to be no greater than 120 VAC, which is well within the normal everyday operating voltage of any standard SPD. And I don’t believe that they pass any significant current at 120 VAC or << …generate heat as a normal byproduct. >> at this voltage. So I don’t understand why they would be subject to a severe temperature rises or failure.

 

I hope I have explained my question clearly. I really appreciate your helping me understand the situation. As I have stated previously, I still don’t understand why having a SPD in an electrical distribution strip is unacceptable while a similar distribution strip without any protection whatever, is acceptable.

 

Tex

I'm no Chengkp75, but here's my thought..fire bad.

Not sure I have the ability to explain further, its been 4 decades since I took classes in electrical theory (some quickie refreshers, but nothing in full detail), so you probably have an advantage over me.

 

Anyway, one point I didn't mention is that ships power is 3-phase down to where it is distributed to the outlets, so between two circuits, there is not necessarily a cut and dried 180 degree phase shift.

 

Now that I think about it, and correct me if I'm wrong, because semi-conductor theory is not my strong point, an SPD built for shore use looks for voltages between the hot leg and ground (using shore terminology), and this voltage alternates between 120 and 0. On a shipboard system, the voltage between the hot leg and ground alternates from +60 to -60. When the voltage is -60 on the hot leg, the neutral leg is at +60, and you have reversed the polarity of the voltage the semi-conductors see. This is what causes the overheating (reversing the polarity of voltage applied to the semi-conductor) which is aggravated when an out of phase ground is introduced.

 

Other than this, I'm out of ways to explain a phenomenon I know happens.

This is hard to discuss without a schematic. But I think I get the gist of it. It all comes down to one sentence in the Coast Guard warning: "For shipboard applications, it is important that protectors interrupt both power leads". On shore, it is okay, even desirable, to allow current from " ground" to neutral. But on ship, the two leads are not so much VCC and GND, but more like V+ and V-. Current between V- and GND is not desired, and so a floating potential exists between those two nodes. If the surge protector interrupts only V+, you create a short between V- and GND; which on shore they should be equipotential anyway. On ship, you trip a breaker or worse. A "certified" surge protector would probably have a second relay switching V-. Some do have that, some don't. Personally I don't see why not all just do. I guess it is somehow better to bleed excess current "harmlessly" to ground, as a lightning rod does, rather than simply optoisolate your valuable device completely.

Hi chengkp75 & tetleytea,

Thank you for the quick and honest response, I really appreciate the time and thought you have put into it. Some quick comments.

The only way that two 60 VAC sinusoidal signals can be combined to form a 120 VAC sinusoidal signal is if the two signals are exactly 180 degrees out of phase. In any other situation, the resultant signal obtained by combining the two original 60 VAC signals will be either a distorted sine wave, not 120 VAC or both.

If I remember my electrical training correctly (and it’s been 50 years for me,) the hot line in a land based house electrical system does not go between 120 and 0 but rather is centered around 0. If it went from 120 to 0 and back, wouldn’t that imply a DC component of around 60 volts in the signal? I don’t believe that this is the case.

The action of a SPD is dependent on the behavior of MOVs (Metal Oxide Varistors), several of which are connected between what is the hot line and the ground line in house wiring. Of course if used in a marine environment, they would be connected between one of the power lines and the “Neutral” line.

Contrary to your assertion, there are no semiconductors in modern MOVs. They are made primarily of powdered Zinc Oxide, ZnO (with traces of other elements,) sintered into a disc shape and then electrical contacts are applied to the two surfaces of the disc. No semiconductors for a bunch of years now.

Varistors have the unique property that under normal circumstances, they have an extremely high electrical resistance. But when a very high electric field is applied across them (i.e. a high voltage across the device), their electrical resistance is reduced significantly. As soon as the high electric field is taken away, their electrical resistance returns back to the original high value. This is the way they “bleed off” the energy of a high voltage spike on an electrical power line. In the presence of the spike, their resistance decreases significantly and the spike’s energy is bled off.

A mechanical analogy to the operation of a MOV (of course not exactly the same, just an analogy) is the operation of an over pressure relief valve on a compressed air tank. If the air pressure gets too high, the pressure relief valve opens just long enough to bleed off the excess pressure and then closes again.

However, when a great amount of energy must be bled off to eliminate a very large electrical spike, a MOV (which is basically a variable resistor) may generate enough heat to burn itself out. If this should occur, the possibility exists that the two connections to the MOV might fuse together and become short circuited. This would be undesirable as these two connections might well be, for example, to a power line and a ground. To compensate for this possibility, a fuse is also incorporated in the SPD in series with the MOVs. So if any of the MOVs burn out and form a short circuit, the fuse will blow to open the circuit and eliminate the problem. The MOV must then be replaced.

By the way, this is the primary reason for the SPD being able to “open” a circuit. It has nothing to do with what is happening in the circuitry outside of the SPD. It has only to do with preventing the SPD from creating an additional problem in the system. Although in certain instances a SPDs may help by opening a circuit, it is not intended to permanently shut off a circuit from excess currents caused by other circuit problems. It is only intended to bleed off the energy of high, extremely short time duration electrical spikes. Time durations usually measured in nanoseconds (billionths of a second.)

So the argument that “SPDs only open one of the two power lines in marine power distribution systems” is a specious argument. SPDs were never intended to function in this manner. They are only intended to protect against high, extremely short duration electrical spikes.

Unfortunately after all of this discussion, I am still left with my original question of why having a SPD (which may help in certain cases but not in others) in an electrical distribution strip is unacceptable while a similar distribution strip without any protection whatever, is acceptable.

Tex

Tex,

Aside from all the technical issues that many of us are struggling to understand, the very simple answer to your question as to why these SPDs are not approved is, "They occasionally start fires".

Fire still remains the greatest danger to life on any ship.

It really doesn't matter why or how they start fires, but they are a fire danger recognized by the Coast Guard and are not recommended for ships use.

We already have quite a few fires on ships, and we usually manage to put them out before anyone is injured or killed.

Do we really need any more fires? Probably not.

But looking at it another way: Your cruise contract on any cruise line holds you legally and financially responsible for any damage you might cause to the ship. It matters not if the damage was intentional - or not.

If you manage to smuggle a forbidden electrical device onboard - and it just happens to start a fire in your cabin - we will most likely be able to detect it in time and safely extinguish that fire. But the cost of the fire damage goes onto your credit card.

A new standard passenger cabin today costs, on average, US$265,000.

Are you feeling lucky?

I'm no Chengkp75, but here's my thought..fire bad.

Hi Elaine5715,

I absolutely agree…fire bad.

SPDs exist in virtually every house in the USA with no significant safety problem being identified. I do not understand and although I have asked, I have never been shown a single example of how the functioning of a SPD on a cruise ship causes a safety problem.

So I am left with the old adage “the plural of “anecdote” is not “data”.

Tex

Tex,

Aside from all the technical issues that many of us are struggling to understand, the very simple answer to your question as to why these SPDs are not approved is, "They occasionally start fires".

Fire still remains the greatest danger to life on any ship.

 

It really doesn't matter why or how they start fires, but they are a fire danger recognized by the Coast Guard and are not recommended for ships use.

 

We already have quite a few fires on ships, and we usually manage to put them out before anyone is injured or killed.

Do we really need any more fires? Probably not.

 

But looking at it another way: Your cruise contract on any cruise line holds you legally and financially responsible for any damage you might cause to the ship. It matters not if the damage was intentional - or not.

If you manage to smuggle a forbidden electrical device onboard - and it just happens to start a fire in your cabin - we will most likely be able to detect it in time and safely extinguish that fire. But the cost of the fire damage goes onto your credit card.

A new standard passenger cabin today costs, on average, US$265,000.

 

Are you feeling lucky?

Hi Bruce,

I need to answer you the same way I just answered Elaine5715.

Even the Coast Guard message on the subject does not explain the details of any problem caused by SPDs. They just state “Most commercially available SPDs are designed for use ashore and will interrupt only the hot conductor when a surge occurs…<snip>…these devices may provide protection in our homes and offices, these same devices may be a fire risk onboard vessels.

But aside from making this assertion, they provide absolutely no information to back it up. The example they give in their message does not even back it up. In fact, I have been unable to find any discussion anywhere about exactly why SPDs may cause fires on cruise ships.

Yes, fires have been caused by electrical devices containing SPDs. But I rather suspect that just as many fires have been caused by electrical devices that do not contain SPDs.

So I need to repeat the old adage “the plural of “anecdote” is not “data”.

By the way, I (as well as any other rational person) do not “smuggle” anything aboard a cruise ship, so the last portion of your message has no meaning for me.

Tex

So the argument that “SPDs only open one of the two power lines in marine power distribution systems” is a specious argument.

I'm not following your logic how that is an "argument" at all; that is straight out of the Coast Guard warning posted on page 1. I'm also not following why the varistor thing is relevant. A surge protector could use switches of any kind: relays, Solid State relays, triacs, MOSFETs, a PNP optoisolation circuit, whatever. Except for the nanosecond response time you referred to (which rules out mechanical relays), the point is that it is a switch. A MOSFET might detect a voltage spike instead of a current spike, but so what.

The point is that your V- is floating on a marine circuit, whereas on shore you at least have some gravitation to GND. The switching logic on your surge protector is keying off of an unknown potential. And when it does, it thinks it is bleeding excess current "safely" to GND, when in fact it is shorting out what should be a floating node. In marine, floating good (pun intended). On shore, floating bad.

Hi Bruce,

 

I need to answer you the same way I just answered Elaine5715.

 

Even the Coast Guard message on the subject does not explain the details of any problem caused by SPDs. They just state “Most commercially available SPDs are designed for use ashore and will interrupt only the hot conductor when a surge occurs…<snip>…these devices may provide protection in our homes and offices, these same devices may be a fire risk onboard vessels.

 

But aside from making this assertion, they provide absolutely no information to back it up. The example they give in their message does not even back it up. In fact, I have been unable to find any discussion anywhere about exactly why SPDs may cause fires on cruise ships.

 

Yes, fires have been caused by electrical devices containing SPDs. But I rather suspect that just as many fires have been caused by electrical devices that do not contain SPDs.

 

So I need to repeat the old adage “the plural of “anecdote” is not “data”.

 

By the way, I (as well as any other rational person) do not “smuggle” anything aboard a cruise ship, so the last portion of your message has no meaning for me.

 

Tex

Tex,

At the end of the day, it all comes down to this, "Our Ship, our rules". It doesn't have to be logical or even make sense.

Tex,

At the end of the day, it all comes down to this, "Our Ship, our rules". It doesn't have to be logical or even make sense.

Hi Bruce,

Thank you for your communication.

The way I interpret your response is that you’re in the same predicament as I am.

I get the impression that except for some anecdotal evidence, you also have no idea why using an electrical distribution strip containing a SPD (which may help in certain cases but not help in others) is unacceptable while a using a similar electrical distribution strip without any protection whatever, is acceptable.

Thank you for sharing this opinion.

Tex

OP, why can't you use an Apple computer with a Windows device? There are all kinds of technical explanations but it comes downs to this- the two devices are not compatible.

Same with the SPD and shipboard wiring. You don't need to know all the whys and wherefores, you just need to know the two systems are not compatible.

Hi Bruce,

 

Thank you for your communication.

 

The way I interpret your response is that you’re in the same predicament as I am.

 

I get the impression that except for some anecdotal evidence, you also have no idea why using an electrical distribution strip containing a SPD (which may help in certain cases but not help in others) is unacceptable while a using a similar electrical distribution strip without any protection whatever, is acceptable.

 

Thank you for sharing this opinion.

 

Tex

Perhaps you can get a better explanation from the experts. I've found that Wright Computer Systems sells a device, the Brooks Power Systems Shipboard Surge Suppressor model Z6-6(2P). This is designed specifically for marine use, and meets milspec CID #A-A-50622. I have only found this milspec for download at $25, so I'm not that interested. Also, Schneider Electric sells the model MPS-6E marine surge suppressor. Perhaps contacting either manufacturer would get you the answer you desire.

Here is a link to milstd1310.g: http://r.search.yahoo.com/_ylt=A0LEVwgsFrJV5EsAFVlXNyoA;_ylu=X3oDMTEyaDV2ZWlpBGNvbG8DYmYxBHBvcwM4BHZ0aWQDQjA1NzhfMQRzZWMDc3I-/RV=2/RE=1437763245/RO=10/RU=http%3a%2f%2fwww.readbag.com%2fearth2-parts-basics-milstd1310g/RK=0/RS=NIWYXGfRUKwJ0PrgEdnTteqDato-

Your search for technical explanations would probably be better served on an technical site, rather than a cruise site. :o

I believe the USCG uses government and industry experts in their investigations, so even though their Safety Notice may not be in the detail you desire (it is intended for ship owners, not electrical engineers), I believe it to be based on science. I also don't believe the USN would develop a spec for a power strip unless there was a need for it.

OP, why can't you use an Apple computer with a Windows device? There are all kinds of technical explanations but it comes downs to this- the two devices are not compatible.

 

Same with the SPD and shipboard wiring. You don't need to know all the whys and wherefores, you just need to know the two systems are not compatible.

Hi sparks1093,

Thanks for the opinion.

I’m afraid that when someone tells me something that doesn’t seem right to me, I simply ask for the reasoning behind the assertion. Most of the time I get a good answer. But occasionally I get a bunch of words that still don’t make sense to me. Than I ask for an explanation.

Now when the “explanation” given to me by knowledgeable people still doesn’t explain the assertion, I ask a second time. I don’t just shrink into the woodwork.

I am a bit familiar with both the Apple Computer operating systems as well as the Windows systems. It is perfectly clear to anyone who wishes to delve into the details, why a Windows or Android device will not respond to an Apple IOS or 10.X system command. It is not magic or some ethereal cosmic law that dictates this, it is simply mathematics and computer programming.

My original posting was that I don’t understand and “…I would appreciate someone explaining …” You have replied << You don't need to know all the whys and wherefores, you just need to know the two systems [insert: SPDs and shipboard electronics] are not compatible. I need to question this statement. I have not found nor been shown, a single incompatibility in the two systems.

At first I received several replies that purported to explain the situation. I carefully answered each reply, showing that indeed, it did not explain the situation. Then there were several anecdotal examples of problems (of undefined causes) with electrical devices. Next there were a couple of replies such as yours that said “it’s not necessary to know why, just go along with the flow” or “it’s too complicated for me to explain” or “if the experts think it’s a problem then it must be so.” These messages mean to me that the authors simply didn’t know the answer to my original posting. I’m afraid it is not in my nature to accept the gist of these assertions.

Electronics is a well defined science. It is not fantastically complicated to those of us with the proper training. The answer to my original question should be explainable in simple language and be capable of being understood by non-expert electrical workers. The fact that I have been unable to find an answer, leads me to wonder whether there is indeed a valid answer to my question or alternatively, is their no answer and the entire problem is simply a form of an urban legend.

I hope this explains more fully why I continue to ask the question of why having a SPD (which may help in certain cases but not help in other cases) in an electrical distribution strip is unacceptable while a similar distribution strip without any protection whatever, is acceptable.

Tex

Perhaps you can get a better explanation from the experts. I've found that Wright Computer Systems sells a device, the Brooks Power Systems Shipboard Surge Suppressor model Z6-6(2P). This is designed specifically for marine use, and meets milspec CID #A-A-50622. I have only found this milspec for download at $25, so I'm not that interested. Also, Schneider Electric sells the model MPS-6E marine surge suppressor. Perhaps contacting either manufacturer would get you the answer you desire.

 

Here is a link to milstd1310.g: http://r.search.yahoo.com/_ylt=A0LEVwgsFrJV5EsAFVlXNyoA;_ylu=X3oDMTEyaDV2ZWlpBGNvbG8DYmYxBHBvcwM4BHZ0aWQDQjA1NzhfMQRzZWMDc3I-/RV=2/RE=1437763245/RO=10/RU=http%3a%2f%2fwww.readbag.com%2fearth2-parts-basics-milstd1310g/RK=0/RS=NIWYXGfRUKwJ0PrgEdnTteqDato-

 

Your search for technical explanations would probably be better served on an technical site, rather than a cruise site. :o

 

I believe the USCG uses government and industry experts in their investigations, so even though their Safety Notice may not be in the detail you desire (it is intended for ship owners, not electrical engineers), I believe it to be based on science. I also don't believe the USN would develop a spec for a power strip unless there was a need for it.

Hi chengkp75

I have reviewed both the Navy MIL-STD-1310G and the Commercial Item Description CID #A-A-50622 you referenced (and I thank you very much for the references) and as I suspected, neither of them says a single thing about any problems involved with the use of commercial SPDs or with any devices incorporating commercial SPDs. They do not forbid, nor in fact even hint at a recommendation against the use of commercially available SPDs. They simply state a requirement for greater protection than an SPD alone can supply. Not that the SPD causes problems, just that they require a higher level of protection.

What MIL-STD-1310G does say is a great deal about electrical grounding and protection against Electromagnetic interference (EMI), Electromagnetic pulse (EMP), Radio frequency interference (RFI) and Intermodulation interference (IMI).

However it also does require that << Any singlephase 115-volt mobile-transportable equipment which is permanently located and is energized more than 50 percent of the time (such as copiers, personal computers and peripherals and soda machines) shall be connected to a separate circuit…<snip>…using a multi-outlet power line strip (surge suppressor) >>. But in this specification, the meaning of the term “surge suppressor” is a device that includes, as well as a SPD, a two powerline (double switched) circuit breaker. This is a more complex and protective device than the simple SPD alone that we have been discussing.

Similar to MIL-SPC-1310G, the other specification (CID #A-A-50622) describes a “surge suppressor” for shipboard use. And here the description actually states “surge suppressors using MOVS for normal mode protection shall include as well as a double pole circuit breaker, a non-resettable thermal cutoff device that interrupts both sides of the supply source.” Recall here that a device including MOV’s with a non-resettable thermal cutoff device (a fuse), is exactly the modern SPD we have been discussing. But in this case, the requirement is for a fuse in both of the power lines. Certainly a good idea.

So here again, absolutely nothing has been said about SPDs causing any problems in shipboard use. The specifications only require that a true circuit breaker be in place to handle potential problems as well as two fuses instead of one. But as I have said previously, modern SPDs were never intended to solve the types of problems that circuit breakers handle, so the requirement of the specification is quite reasonable. I also believe that a dual circuit breaker is highly desirable. And I also still do not understand where or how a SPD creates any problem when included in the circuit. It simply does not solve some of the problems that a circuit breaker can solve.

You say the government uses industry experts in their investigations. I agree with you completely. In fact, I personally have written a number of military Specification Control Drawings and Ordinance Documents for the Navy dealing with the construction and reliability of submarine based missile guidance systems. But whether or not any particular document is complete depends on the document, not on the author. And in my opinion, the Marine Safety Alert #03-13b does not contain sufficient information to conclude that the problem experienced was due to the stated cause.

Also, you say << I also don't believe the USN would develop a spec for a power strip unless there was a need for it.>> As I have shown above, I believe the purpose for the spec is to provide a higher level of protection than that which would be obtained from a SPD alone. Not that the SPD would cause a problem, just that we can improve on it and do better.

But now lets look at an electrical powerline strip containing a SPD compared to one that contains no protection whatsoever. In either case, these devices contain no circuit breaker in the circuit. However I still don’t understand why having a SPD (which may help in certain cases but not help in other cases) in an electrical powerline strip is unacceptable while a similar powerline strip without any protection whatsoever, is acceptable.

Tex