Power outlet strips

I understand that HAL does not like passengers using power outlet strips that contain surge suppressors. Does anyone know exactly why?

I don’t mean to be picky here, but I’m not looking for “there once was a problem on,,,”, “so and so says they may pose a problem”, “the coast guard once put out a warning based on some experience on a tramp steamer”, “my brother-in–law’s first cousin twice removed roommate’s ex wife (whom I have never met or even spoken with) had one overheat”, or “look over previous threads on this subject” (by the way which I have done and found no accurate detailed information), etc.

I’d like to know if anyone knows technically exactly what problem is being faced with the use of these power strips. I have a background in Electrical Engineering and am looking for a technical rather than a legal or emotional reason.

Thanks in advance.

Scott & Karen

Give Page two of this document a once-over.

http://www.omao.noaa.gov/noaafleetinspection/safety_alerts/Surge%20Suppressors%20USCG%20Safety%20Alert%20April%202013.pdf

Since the wiring can be different, where their is a 50/50 chance of getting it wrong not permitting at all is the wise course of action.

You'll find this thread has some good information, particularly that provided by chengkp75:

http://boards.cruisecritic.com/showthread.php?t=2228714&highlight=surge

Hi guys,

Thanks for the info. but unfortunately I'm still in a quandary.

Give Page two of this document a once-over.

 

http://www.omao.noaa.gov/noaafleetinspection/safety_alerts/Surge%20Suppressors%20USCG%20Safety%20Alert%20April%202013.pdf

 

Since the wiring can be different, where their is a 50/50 chance of getting it wrong not permitting at all is the wise course of action.

I believe the Coast Guard “Marine Safety Alert” you reference is extremely misleading. It confuses the situation by using the term SPD (Surge Protection Device) to refer to the entire power strip rather than the specific small surge protection device (called a MOV or a metal oxide varister) contained within the power strip. This is the part of the power strip that affords the actual surge protection. The alert actually says “…Here lies the problem with inexpensive and older SPDs that only disconnect one “hot” terminal lead. The other “hot” terminal remains hot…” So the problem being discussed has nothing whatever to do with the surge protection device (MOV) contained within the power strip. It has only to do with the way the power strip containing the MOV was wired. In other words, whether or not the power strip contained a MOV is irrelevant. But realize here that HAL ships are allowing power strips without MOVs but not allowing those that contain MOVs.

You'll find this thread has some good information, particularly that provided by chengkp75:

 

http://boards.cruisecritic.com/showthread.php?t=2228714&highlight=surge

On this thread are the standard “someone had a problem (undefined cause)”, “extension cords are allowed”, “extension cords are not allowed”, “I used this thingy”, “this thingy is not allowed”, “surge protectors should not be used,”, “surge protectors pose no problem”, etc. But as I have found with several old threads, nothing is said about what is the problem with using a surge protection device (a MOV) contained within a power strip. It seems that “chengkp75” has posted several discussions about this subject and seems quite knowledgeable, but in any of his posts I can find no definition of what is the specific problem.

So I appreciate the references and I guess I’ll hope there is some additional information on this board. Meanwhile I'll keep on hunting to see if I can find an answer.

Scott & Karen

Have you seen this paragraph by chengkp75? (Bolding mine)

The reason surge protectors are not allowed is that ship's power systems are different than shore power systems that the surge protectors are designed for. On land, one of the "legs" of the power system (one of the flat pins that carry current) is grounded to the ground pin (round one needed to protect you from electric shock) at your circuit breaker panel. Ships keep these two wires separate, so that stray current does not flow through the "ground" which is the ship's hull. These stray currents will create a mild battery effect in sea water, causing corrosion to the hull. Therefore, there are monitoring and alarm circuits onboard that measure the amount of current flowing in the hull, and surge protectors can set off these alarms.

You can get an 'approved' power strip from the front desk but go early as they go fast.

I understand that HAL does not like passengers using power outlet strips that contain surge suppressors. Does anyone know exactly why?

 

I don’t mean to be picky here, but I’m not looking for “there once was a problem on,,,”, “so and so says they may pose a problem”, “the coast guard once put out a warning based on some experience on a tramp steamer”, “my brother-in–law’s first cousin twice removed roommate’s ex wife (whom I have never met or even spoken with) had one overheat”, or “look over previous threads on this subject” (by the way which I have done and found no accurate detailed information), etc.

 

I’d like to know if anyone knows technically exactly what problem is being faced with the use of these power strips. I have a background in Electrical Engineering and am looking for a technical rather than a legal or emotional reason.

 

Thanks in advance.

 

Scott & Karen

The last time I responded to a thread like this was before my last work tour, so I'm going to be lazy and not search for the exact thread or posts. I'll let you do the leg work and come back and tell us your findings.

As I told the other OP, I can't imagine why someone with an EE background would look for a technical answer on this forum, rather than on an engineering site, but okay. If you search my previous posts, you will find that I provided the OP with links to not only the USCG investigative and research branches, but to professors of marine engineering at state and federal maritime academies. I suggest you contact them for your answers. I'm sure the profs will be more than happy to answer. I may not fully understand the physics of it, but I will base my actions and recommendations on the USCG report (as the cruise lines and their insurers are) and my 40 years of practical experience with marine electrical systems and the problems I have personally experienced with surge suppressor on ships.

You can get an 'approved' power strip from the front desk but go early as they go fast.

For anyone wondering, if a power strip ad and packaging doesn't specifically say that it has a s-s, it most likely doesn't have one.

Against my better judgement, I'll try this again. MOV's are designed to allow current to flow for milliseconds, as in lightning strikes. Since the resistance of an MOV vares with the voltage, and resistance generates heat, an MOV subject to extended current flow will overheat. Even at normal voltage, since the (shoreside) neutral and the ground on a ship are not at the same voltage, there will be a continuous leakage current (not much, but 24/7), which can cause the MOV to overheat. This leakage current is how the ship knows that a surge suppressor is installed, since we continually monitor current flow from conductors to ground.

I need to start this posting by apologizing for the following rather long and technically involved discussion. I hope it does not turn off too many readers but also, that it does convince other readers of the warning it presents. It is fascinating to me that so much misleading, partially incorrect and totally incorrect information, as well as some honest, accurate and important information, has been posted about this subject in the past.

From what “chengkp75” has stated previously, <<…I may not fully understand the physics of it…>>, unfortunately even he seems to not understand fully the details of the problem with using power strips that contain MOVs. These are Metal-Oxide-Varistors, the specific device contained within most power strips that creates the surge suppression effect at a designed “trigger” clamping voltage level. He has simply continually presented that in his experience, problems have occurred with their use. And this can be some extremely valuable experience. But here I think I recall reading on one of the previous threads, it is important to realize that “The Plural of Anecdote Is Not Data.,” … or in other words … a few problems experienced in the past do not necessarily demonstrate an ongoing problem.

So after perusing several of the older threads on potential problems with the shipboard use of power strips containing MOV surge suppression devices (and being thoroughly confused,) I decided to follow the recommendation of “chengkp75” and attempt contacting academic experts in the field. I sent query’s to the Massachusetts Maritime Academy, Marine Systems Eng. Dept. of Texas A&M Univ., Eng. Dept. of US Naval Academy, Merchant Marine Academy and several other organizations recognized as expert in the field.

I explained the conundrum I was facing in not being permitted to use power strips containing MOVs but being permitted to use power strips not containing MOVs, even though millions of power strips containing MOVs were being used daily with no apparent major problem. And that my technical background in the design and reliability analysis of airborne and space borne guidance and control systems left me without any experience with shipboard electrical power systems.

The most interesting response I received was from a professor at Texas A&M. His message, typically cryptic as professors are wont to be, was << Due to scr’s [silicon-Controlled-Rectifiers (my insertion)] for the main propulsion and the pulse width modulation, the electricity is dirty, lots of spikes, the varistors and the diodes operating in the reverse polarity ,,,,,,, can overheat and start fires >>

So this set me off on a search for information on the possible degradation and any undesirable characteristics of MOVs after experiencing repeated non catastrophic electrical spikes. I knew of course that a huge electrical spike could easily damage a MOV but knew nothing of the effect of repeated lower level spikes. Thank goodness for the internet. Thirty years ago this search would have meant many, many days or weeks spent in various libraries, but now the search could be done from my own desk at home. And what do you know? I found several references directly on point. But rather than present them all here, I would like to include only the following illustrative snippets.

<< MOVs have a finite life expectancy and “degrade” when exposed to a few large transients, or many smaller transients.[18][19] As a MOV degrades, its triggering voltage falls lower and lower >> … << If used in a power filtering application, eventually the MOV behaves as a part-time effective short circuit on a power line line which will cause it to heat up, starting a process called “thermal runaway.” As the MOV heats up, it may degrade further, causing a catastrophic failure that can result in a small explosion or fire >> … <<A failing MOV is a fire risk, which is a reason for the National Fire Protection Association’s (NFPA)[21] UL1449 in 1986 [22] and subsequent revisions in 1998 and 2009. NFPA’s primary concern is protection from fire >> … << A thermal fuse or some equivalent solution [is necessary to (my insertion)] protect from MOV generated hazards >> … << Because of their good price/performance ratio, MOVs are the most common protector component in low-cost basic AC power protectors. >> I will be glad to supply the references cited in the discussion to anyone who is interested, but I thought it would be too much information to include in this posting.

Now here we must realize that the thermal fuse mentioned as required to protect a MOV circuit, is different from a common circuit breaker or fuse which opens to prevent current flow after a certain level of current is exceeded in a circuit. A thermal breaker opens when a given temperature is exceeded. So a MOV in thermal runaway may be getting hot but only conducting, say, 5 amps of current and a common power strip circuit breaker set to limit the current at, say 15 amps, would never open. In this case, the MOV might continue to get hotter and hotter until a meltdown of the power strip or a fire occurred. However, a thermal breaker would have opened as the MOV got hot. Unfortunately, most commonly available power strips which may contain circuit breakers, do not contain thermal breakers. In fact, there have been documented cases of secretaries reporting smoke and fire coming from power strips containing MOVs, under desks while the computers on the desks continued functioning normally.

So the gist of this long and technical discussion is that I am now convinced that the warnings continually presented by “chengkp75“ have been perfectly valid and I need to complement him on his steadfastness in presenting this information, even in the face of many other posters who doubted the veracity of his warnings.

I now understand why power strips containing MOV surge suppressive devices should not be used in shipboard applications and in the future, I shall be an advocate of banning the shipboard use of power strips containing MOVs.

Scott & Karen Bonis

Thank you CaveDiving for your time and effort researching this matter, and sharing the outcome.

Sent from my iPad using Tapatalk

Thank you both CaveDiving and Chengkp75 for the clarification and to CaveDiving especially for breaking it down as he did and posting it is black and white with thought to how the laymen can understand it.

You guys Rock!!

I have copied CaveDiving's post above and will reference whenever the subject comes up again.

Joanie

Thanks, CaveDiving. I accepted Chengkp75's warnings from the first time I read them, but it's great to see that an enquiring mind and solid research confirmed his findings. Well done, both of you! :)