Reverse Polarity?

[Carmel2]

How damaging is it on a regular AWB over the course of a week or so?

 

[nigelmercier]

Be more specific please.

 

[Carmel2]

Be more specific please.

If I was to plug into shore power box that had been wired wrongly, ie it delivered a reverse polarity, how damaging could that be over the course of a week or so..................

 

[nigelmercier]

Not at all damaging, assuming you are still alive.

Could cause problems if there is no Galvanic Isolator, but I imagine as a liveaboard you have one.

 

[macd]

I'm no sparks, but understand that with a single-pole breaker, reversed polarity is dangerous since by switching it 'off', you're actually turning off only the neutral, so shore power circuits will still be live. (Nothing on them will work, since there's no return, but if you go poking about...)

If your incoming shore-power breaker is a bi-pole, as it should be, probably no harm done.

 

[sailaboutvic]

Paul I have a small lead which is the other way round and any time I come across the problem I just use the lead .i have found reverse polarity can be quite common in places .

 

[whiteoaks7]

These things are useful http://www.maplin.co.uk/p/mains-socket-tester-wd53h - three red lights and everything is ok.

We often find polarity reversed even between individual boxes in our yard and so we too have a 'reversing lead'.

Circuit breakers in shore supplies can be single pole so if they blow before the one on your boat you won't be protected.

 

[heart of oak]

You may find that your microwave turns into a freezer............................................................................................................:eagerness:

 

[Mad Pad]

We have an indicator switch fitted.If the green goes off and the red comes on just flick the switch.

 

[Seren]

Where did you get such a useful bit of kit or did you make it up yourself? Bit dim when it comes to electric so would appreciate advice - have an aluminium boat also!

 

[Carmel2]

We have a light on the board that tells me when it happens, I think I will knock a lead thats in reverse. Thanks for the info folks.

 

[RupertW]

I have a combination of the two above - the maplin mains indicator and a short lead that reverses polarity. Probably use it about half the time in marinas.

I made it from B&Q 25 amp cable (cut off my main cable) and male & female plug/sockets, then marked it so very clear what it does. Very simple to do - one end (doesn't matter which) is wired correctly, on the other one you put live wire into neutral hole and vice versa. And with the 3 light maplin plug you can check that it's now ok before you switch any other plugs on.

 

[<152587>]

No prob at all as AC is constantly alternating high to low at whatever the frequency is. To rectify either build a rotary switch arrangement with indicators thus allowing you to manually change polarity or wire an insulating transformer incoming which will sort it out automatically and benefit the installation by breaking the earth route from the boat to the shore thus removing the possibility of stray earth currents

As stressed in previous posts the danger is single poled breakers or indeed fuses, always fit double pole breakers.

A simple delta indicator may be constructed from 3 neon indicators.

Neon 1 wired neg to earth indicates reverse polarity only illuminated when reverse polarity present
Neon 2 wired pos to earth indicates healthy earth. Normally on.
Neon 3 wired pos to neg indicates healthy supply. Normally on.

Note that Neons 2&3 should be equal brightness.

 

[GrahamM376]

If I was to plug into shore power box that had been wired wrongly, ie it delivered a reverse polarity, how damaging could that be over the course of a week or so..................

Most 240v equipment (battery charger, TV, microwave, kettle, etc) these days is double insulated and often comes with an alternative 2 pin euro plug with a 50/50 chance of reversed polarity so no problems with safety or damage, unlike very old electrical goods where the chassis would be live if connected the wrong way. We often come across reverse polarity in marinas and just don't worry about it.

 

[nigelmercier]

No prob at all as AC is constantly alternating high to low at whatever the frequency is...

While this is true, the ramifications are far deeper than you state.

 

[FullCircle]

I have a Polarity plug, as suggested below..

https://www.amazon.co.uk/kenable-Socket-Tester-Polarity-Checker/dp/B007JIRFYU which at £2.60 is hardly breaking the bank.

I made up a lead (around £9 using caravan shop plugs and socket, spare bit of mains cable) that goes between my incoming shore power lead and the input socket to the AC power fuse box which reverses polarity, which I use if the plug socket tester shows a 'fault'. This is simple cheap and effective.

 

[RupertW]

I have a Polarity plug, as suggested below..

https://www.amazon.co.uk/kenable-Socket-Tester-Polarity-Checker/dp/B007JIRFYU which at £2.60 is hardly breaking the bank.

I made up a lead (around £9 using caravan shop plugs and socket, spare bit of mains cable) that goes between my incoming shore power lead and the input socket to the AC power fuse box which reverses polarity, which I use if the plug socket tester shows a 'fault'. This is simple cheap and effective.

Have I just been Lakesailored, or does that involve the OP thanking FullCircle to complete it

 

[maby]

While this is true, the ramifications are far deeper than you state.

Indeed... you can leave it with the polarity reversed pretty much indefinitely without damaging the boat, but it may negate some of the protection measures built into the wiring to protect the occupants.

 

[<152587>]

Indeed... you can leave it with the polarity reversed pretty much indefinitely without damaging the boat, but it may negate some of the protection measures built into the wiring to protect the occupants.[/Q

Which if you read the post in context, yes you can leave the polarity reversed indefinitely without damaging the boat which was the original question. I then defined the hazards and suggested a couple of fixes to rectify and monitor the supply.

The installation of an isolation transformer would be my preferred fix in this particular installation given metal hull.

 

[FullCircle]

Have I just been Lakesailored, or does that involve the OP thanking FullCircle to complete it

Dont think so, I read that yours is not a lead between shore power and socket inlet to boat?