Lethal electrical installation


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Dick
Dick
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Steve Houssart - 2/26/2020
Dick - 2/25/2020
Philip Heaton - 2/25/2020
Some observations on this.  

First, the male plug and female socket at the boat end of shore power is borderline criminal - surely the boat builder did not do this unless it was self-build.

16 months ago I plugged in our 1kw fan heater inside the boat. After a while I noticed an inappropriate smell.  We have EU sockets and UK plugs so use adapters (too lazy to change the plugs) and it was the adapter working itself up into a right state, as in it was getting ready to burn the boat down.  After switching off the shore power and letting things cool down, close inspection  showed that the brass pins of the plug had built up a layer of crud.  Cleaning with emery paper did the trick.  Since then every plug gets a good dose of inspection before it goes in a socket and the plugs are now on the regular maintenance list.

The other issue is that following one of those "let's scare each other to death" cruiser conversations and given my total ignorance about matters electrical, I bought a polarity tester plug to check for reverse polarity in marinas.  I also made up a plug and socket to reverse the reverse polarity - turned out that the marina where we were berthed (Albufeira, Potrugal) did indeed have reverse polarity.  Anyway, I am not sure how important this is but I religiously check every marina we visit - all good since Portugal.

Hi Phillip,
Checking one’s AC outlets on a boat after plugging in to shore power is wise. Reverse polarity is fairly common. I would say in my 5 years in the Med. 20+% of the shore power was reverse polarity. I also had cobbled together a plug pigtail to “reverse” polarity back to correct. (A good tester just plugs into a regular outlet and also gives indication of correct ground or if ground wire and load or neutral are exchanged: much less complicated than a VOM meter and easier to read.)
In the following, please be clear I am not an electrician, and I would love someone with real knowledge to weigh in and correct errors or confirm what I say.
Having the correct polarity (we are talking about the load and neutral wires, not the ground/safety green wire) is potentially quite important as many appliances depend on correct polarity in their design to ensure safety. Having a reverse polarity incoming to an internally damaged appliance (it may still work) might make the metal shell (or other metal parts) carry power and make electric shock likely. This is even more insidious as reverse polarity still allows many appliances to function and give no indication of their being dangerous.
My best, Dick Stevenson, s/v Alchemy

Dick/Philip, nowadays reverse polarity is not so much of an issue as the majority of everyday appliances that we use onboard are more commonly double insulated, which means they have a small built-in transformer, so are not earthed and are often plastic, such as hairdryers, drills, and iPad/phone chargers, etc,
The real issue with reverse polarity is with metal cased items that are earthed, the issue is that often the switch is in the live side of the appliance, meaning that although you've switched off at the appliance the live is still going through the neutral side of the circuit.
An earth fault is caused by the Positive shorting to a metal earth casing, thankfully most modern marinas and generally, most modern boats should have protection for this (ELCB – Earth leakage circuit breaker)) and should in most cases "trip". A negative to earth without an ELCB in the circuit would not necessarily cause shock. The safest way to combat these below-standard electrical supplies and deal with such shortfalls as marina based reverse polarity is to put an isolation transformer in line with your shore supply this also acts as a type of galvanic isolator and also stops unnecessary corrosion also caused by stray voltages going to earth.
The cost for a 2kw version of these starts at £400 up to a 7kva at £700 which initially seems a lot, but a small price to pay for peace of mind and boat safety. If you have concerns about your boat electrics then get a local experienced electrician to give your boat the once over and as a minimum, I would ensure that you install an ELCB between your internal electrical circuit and your shore power socket. However, If you are going to visit many different marinas, particularly abroad then consideration for the investment into an Isolation transformer would be wise.




Hi Phillip,
Thanks for the fill. I had not known that some appliances were being made to ensure safety, although it sounds like there are still appliances where reverse polarity could still be a problem. (Perhaps there is a US/EU discrepancy in standards?)
ELCBs certainly sound like they are a coming thing, much like GFIs have crept into everyday life on shore and on boats, to the safety benefit of all. My research a few years ago indicated that ELCBs were experienced as problematic by skippers who wandered widely: there were lots of false tripping among those cruisers who wandered in the more marginal areas where more modern electrical installations with clean power are harder to come by. What has your experience been?
There is no question in my mind that well-built marine grade isolation transformers are the gold standard of a vessel’s shore power system. I think they are less common than might be wise because: 1. They are quite heavy awkward items that demand a not small amount of real estate, hard to come by on smaller boats, 2. They are fairly expensive, especially as there is little regularly perceived problem they solve nor new benefit readily apparent, and 3. They are probably a bit intimidating for many skippers to self-install and a marine electrician just adds to the cost.
ELCBs and isolation transformers are the kinds of safety kit that, I suspect, will not be common on boats till some regulatory agency demands them or, better still, the marine buying public educates itself on what is important and demands them.
In the meantime, I am not holding my breath and we must rely on letters like yours to get the message out.
My best, Dick Stevenson, s/v Alchemy

Philip Heaton
Philip Heaton
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Hi Steve
Interesting that you mention an isolation transformer as as safety device for reverse polarity.  We contemplated fitting one as we have an aluminium boat but given both the weight and cost we went for a galvanic isolator - does this provide the same safety feature and therefore do I need to carry on testing for reverse polarity?  Disclaimer - in the event that I electrocute myself or some-one else you will not be held accountable by me ... cannnot speak for the missus though ...
Dick
Dick
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Philip Heaton - 2/27/2020
Hi Steve
Interesting that you mention an isolation transformer as as safety device for reverse polarity.  We contemplated fitting one as we have an aluminium boat but given both the weight and cost we went for a galvanic isolator - does this provide the same safety feature and therefore do I need to carry on testing for reverse polarity?  Disclaimer - in the event that I electrocute myself or some-one else you will not be held accountable by me ... cannnot speak for the missus though ...

Hi Philip,
My friends with metal boats believe that every metal boat should have an isolation transformer. Not having a metal boat, I have forgotten the details of their arguments, but believe it has something to do with the IT sitting guard between the shore power AC input and the boat’s AC system, thereby providing isolation from shore power limitations, from green wire connection to other boats (and the problems that can occur, corrosion, from other boats defective wiring) as well as all the benefits of a galvanic isolator.
I do not believe that a galvanic isolator will correct or in any way effect reverse polarization while I suspect an IT will correct faults in AC shore power systems such as this.
My best, Dick


Philip Heaton
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Dick
Thank you for this.  When we had the boat in build we had long discussions about this issue and an isolation transformer is of course superior to a galvanic islolator.  Our thinking was that we would spend most of our time at anchor and visit marinas rarely, which has proved to be the case until the last couple of years, and so weight and cost could be a consideration.  The GI could provide the main hull protection.  It seems from what you are saying that I had better keep on checking with our trusty reverse polarity test plug and have the reverse reverse polarity lead at the ready.

Best wishes Phil
Dick
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Philip Heaton - 2/28/2020
Dick
Thank you for this.  When we had the boat in build we had long discussions about this issue and an isolation transformer is of course superior to a galvanic islolator.  Our thinking was that we would spend most of our time at anchor and visit marinas rarely, which has proved to be the case until the last couple of years, and so weight and cost could be a consideration.  The GI could provide the main hull protection.  It seems from what you are saying that I had better keep on checking with our trusty reverse polarity test plug and have the reverse reverse polarity lead at the ready.

Best wishes Phil

Hi Philip,
You might also check some of Steve D'Antonio's writing on the subject or the Attainable Adventures web site for more information about why an IT is really important for a metal boat: I think it goes beyond galvanic isolation, but I do not remember any details. If you do so, please report back as I am curious. My best, Dick
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