Reverse polarity. Dangerous?

[bedouin]

Back in my student days one of the sockets in my rooms was wired the wrong way round. I discovered this when my Toaster went up in smoke. A fault in the toaster shorted neutral and earth - no big deal except if the neutral is actually live and the only protection is the fuse/breaker on the entire ring circuit.

The frightening bit is that I have been known to poke around inside a toaster with a knife - first checking that the power is switched off but not necessarily unplugging. That could have been very nasty

 

[Spirit (of Glenans)]

Yes, it is potentially dangerous. Most likely your fuse only breaks the hot wire. If reversed polarity in case of over current the fuse will break the neutral. And if you over current is caused by a short between hot and ground to break the Neutral will not solve the problem, so better be very careful!

For UK and Irish forumites, "Hot " is the word used in the US to indicate the "Line", (or "Live") side of the supply, and "Ground" is "Earth".

 

[Spirit (of Glenans)]

If the current keeps reversing polarity, how does my polarity alarm recognise the difference?

As I have a double-pole isolator and an RCD fitted aboard, it does sound from what is being said that it should not be dangerous.

An ordinary phase tester will light up for Line and not do so for Neutral.
It has been mentioned previously on these forums that a plug-in device is available for testing the polarity of sockets and would be useful when plugging in in an unfamiliar marina.

 

[superheat6k]

An ordinary phase tester will light up for Line and not do so for Neutral.
It has been mentioned previously on these forums that a plug-in device is available for testing the polarity of sockets and would be useful when plugging in in an unfamiliar marina.

Always, and report to the duty marina staff the non compliance with IET BS 7671 (16th, 17th or 18th edition) if ever you find a reversed pontoon power outlet. Make sure you do this in writing, ideally by email, and advise the local Environmental Health department will also be informed of the potentially lethal situation. This should draw the necessary attention to the problem.

 

[AndrewB]

Always, and report to the duty marina staff the non compliance with IET BS 7671 (16th, 17th or 18th edition) if ever you find a reversed pontoon power outlet. Make sure you do this in writing, ideally by email, and advise the local Environmental Health department will also be informed of the potentially lethal situation. This should draw the necessary attention to the problem.

It's a matter of psychology. My marina isn't bad at responding to berth-holder problems, but I like to focus on the ones that really affect me, and not get a reputation as being forever complaining; specially not as a troublemaker who is liable to bring down outside bureaucracy on their heads if he doesn't get his way.

Nevertheless, I would press them harder if there was solid evidence that reverse polarity is as dangerous in practice as it might seem in theory. For example, statistics on yachties being electrocuted and boats gone up in flames. That was in part the purpose of my question. However, so far in this thread there hasn't been any reference to actual incidents afloat.

 

[Hoolie]

In practice there's not much risk. On our boat we don't use a lot of mains appliances; a kettle and induction hob mainly with occasional soldering iron and fan heater. None of which is a hazard whatever the polarity. It's just the electrical panel warning light that is a continual reminder!

 

[Aurai]

Another angle, or at least my angle, the faulty socket should be locked off. The assessment for Marina electrics includes that wet stuff called water, all parts of the safety chain should be complete. From design through to install and testing this seems a fail. It would be interesting to see the installation certificate and schedule of test results for this pillar.

 

[Laysula]

Ask the marina if the u=their insurance company know that the wiring is wrong.

 

[st599]

Always, and report to the duty marina staff the non compliance with IET BS 7671 (16th, 17th or 18th edition) if ever you find a reversed pontoon power outlet. Make sure you do this in writing, ideally by email, and advise the local Environmental Health department will also be informed of the potentially lethal situation. This should draw the necessary attention to the problem.

As the OPs location is Dover/Corfu, could the reversal be in Corfu, where centre tapped Earth and double-pole breakers are more common.

Still an issue for someone using UK appliances on board.

 

[Hoolie]

I've come across reverse polarity lots of times and to take them up with the marina/port each time would be a life-time endeavour. Plug in a polarity reverser when needed and move on

 

[Alex_Blackwood]

As the OPs location is Dover/Corfu, could the reversal be in Corfu, where centre tapped Earth and double-pole breakers are more common.

Still an issue for someone using UK appliances on board.

If the OP is referring to a Marina in the UK covered by BS7671 (18th Edition is the current one) then the installation should have an annual Installation Inspection where reversed line and neutral (polarity ) should be part of the inspection. An Installation Condition Report will be raised and the reversal highlighted and should be corrected. All marina outlets require to be protected with double pole RCD's and MCB's or RCBO's. What Heath Robinson set up you have on your boat is your responsibility.

 

[thinwater]

This should ALWAYS be brought to the marina's attention in writing and framed in this manner; if the boat has an improper secondary ground (common) this can easily create a lethal electric shock drowning hazard, and that liability will likely be 100% on them. There is no acceptable excuse. People die from this every year in the US (freshwater).

My normal approach is not to plug in. I don't really need to.

 

[Beneteau381]

If the current keeps reversing polarity, how does my polarity alarm recognise the difference?

As I have a double-pole isolator and an RCD fitted aboard, it does sound from what is being said that it should not be dangerous.

A
An issue can arise in something like a toaster, the thing appears switched off, someone sees a bitof burned toast inside and decides to prod it! In a reverse polarity system, the neutral is switched off but the live to the element isnt! Hellooo!

 

[john_morris_uk]

I have a short socket to plug cable that reverses the polarity. It's surprising how often it's needed!

Likewise.

 

[john_morris_uk]

If the current keeps reversing polarity, how does my polarity alarm recognise the difference?

As I have a double-pole isolator and an RCD fitted aboard, it does sound from what is being said that it should not be dangerous.

Polarity is a misnomer in this context.

It's all a question of neutral being connected to earth as some point. (Sometimes this is way back at the substation!)

Lots of Youtube explanations but this is a good one:

Watch it through and the problems are mentioned at 12 minutes 30 onwards or thereabouts.

 

[VicS]

If the current keeps reversing polarity, how does my polarity alarm recognise the difference?

As I have a double-pole isolator and an RCD fitted aboard, it does sound from what is being said that it should not be dangerous.

As just said "polarity" is a misnomer in the context of AC supplies.

What your "polarity" detector is doing is detecting that you have the line and neutral reversed.

JW's videos are excellent but this one is probably rather OTT as far as your incorrect polarity indication is concerned, but watch and enjoy .
Some of his "fun" videos are good entertainment .

 

[Birdseye]

I have a short socket to plug cable that reverses the polarity. It's surprising how often it's needed!

Me too.

 

[Alex_Blackwood]

Polarity is a misnomer in this context.

It's all a question of neutral being connected to earth as some point. (Sometimes this is way back at the substation!)

Lots of Youtube explanations but this is a good one:

Watch it through and the problems are mentioned at 12 minutes 30 onwards or thereabouts.

Should be pointed out that the earthing system for marinas (UK) is the TT system. No other system is allowed. When I say marinas I mean the pontoon outlets, not clubhouses and buildings. These will be most likely PME.
The figures below are for a typical marina bollard on a TT system. They show an Earth Loop Impedance of 0.27 ohm, a short circuit current of 850 amps and a trip time for the MCB of 0.4sec.
Not quite equating to some of the figures stated in the video. Not saying he is wrong, possibly misleading?

 

[Deleted member 36384]

This is a very interesting thread. I have low knowledge of mains electrical supply beyond wiring up a 3 x pin plug. The video posted by John was very informative. My own boat's 240V power was fitted by an unknown person before I bought it, consisting of a consumer panel with RCD and MCBs for each of the consumers (ring main, fridge, hot water tank, spare out let) and a galvanic isolator. It appears to be a professional installation. I will be purchasing a polarity tester and a reversing lead as a result of this thread.

 

[VicS]

Should be pointed out that the earthing system for marinas (UK) is the TT system. No other system is allowed. When I say marinas I mean the pontoon outlets, not clubhouses and buildings. These will be most likely PME.

Pontoon supplies are earthed to a local earth rod /rods or similar?
I thought they should be a TN -S system or is that simply not an available option.
.