RCD - sensitive to L/N swapped?

[GHA]

Luckily I did some testing before getting all grumpy and shouting at the boatyard that the power was off again...

RCD, can't be that old but wouldn't stay engaged so new one solved that. But the multimeter did show that there was voltage between neutral & earth with next to none between live & earth. Pretty certain it wasn't like that not so long ago and very possible that someone replugged in the euro plug "upside down" in the box. Rewired the ceeform so live is live once more.

So would the RCD not like that, could that be a possible cause of failure? Or maybe more likely getting damp in a rain shower?

Also, got given a couple of 240v mains LED drivers so thinking maybe wire one between the neutral and earth with a resistor and low power LED as an indicator to alert if the live/neutral isn't as it should be - any reason that wouldn't work? Maybe on the RCD out, though wonder if it would pull enough amps to trip the RCD if the L/N are the wrong way round..

Any thoughts?

TIA

 

[AntarcticPilot]

Luckily I did some testing before getting all grumpy and shouting at the boatyard that the power was off again...

RCD, can't be that old but wouldn't stay engaged so new one solved that. But the multimeter did show that there was voltage between neutral & earth with next to none between live & earth. Pretty certain it wasn't like that not so long ago and very possible that someone replugged in the euro plug "upside down" in the box. Rewired the ceeform so live is live once more.

So would the RCD not like that, could that be a possible cause of failure? Or maybe more likely getting damp in a rain shower?

Also, got given a couple of 240v mains LED drivers so thinking maybe wire one between the neutral and earth with a resistor and low power LED as an indicator to alert if the live/neutral isn't as it should be - any reason that wouldn't work? Maybe on the RCD out, though wonder if it would pull enough amps to trip the RCD if the L/N are the wrong way round..

Any thoughts?

TIA

I recently installed an RCD, and had it wouldn't work initially. Turned out I'd got Live and Neutral swapped at the inlet socket. So yes, getting live and neutral swapped doesn't work!

 

[GHA]

I recently installed an RCD, and had it wouldn't work initially. Turned out I'd got Live and Neutral swapped at the inlet socket. So yes, getting live and neutral swapped doesn't work!

Now can't remember if I tried the new one before swapping L/N to what they should be, old one is definitely a gonner though. Another unknown is when the L/N swapping happened, worked fine then couple days ago didn't...

 

[rogerthebodger]

Also, got given a couple of 240v mains LED drivers so thinking maybe wire one between the neutral and earth with a resistor and low power LED as an indicator to alert if the live/neutral isn't as it should be - any reason that wouldn't work? Maybe on the RCD out, though wonder if it would pull enough amps to trip the RCD if the L/N are the wrong way round..

Any thoughts?

TIA

Just fit and old fashioned neon indicator between L/E and N/E.

I have a green neon L/E (should be on) and a red neon between N/E should be off.

There will be about 2 mA flowing through the RCD but should not cause a problem.

 

[BabaYaga]

Also, got given a couple of 240v mains LED drivers so thinking maybe wire one between the neutral and earth with a resistor and low power LED as an indicator to alert if the live/neutral isn't as it should be - any reason that wouldn't work? Maybe on the RCD out, though wonder if it would pull enough amps to trip the RCD if the L/N are the wrong way round..

Any thoughts?

TIA

Would it not be easier (and safer) to fit a two pole RCD, the type used in Europe (for non polarized AC)?

 

[GHA]

Would it not be easier (and safer) to fit a two pole RCD, the type used in Europe (for non polarized AC)?

The old one and new one seem identical, both have just 2 connections in & out, L & N. Bought in Portugal.

Not sure how that is safer with no indication if there's live up the neutral?

 

[BabaYaga]

I recently installed an RCD, and had it wouldn't work initially. Turned out I'd got Live and Neutral swapped at the inlet socket. So yes, getting live and neutral swapped doesn't work!

The old one and new one seem identical, both have just 2 connections in & out, L & N. Bought in Portugal.

Not sure how that is safer with no indication if there's live up the neutral?

OK, if bought in Portugal it is presumably two pole. The comment above states that getting live and neutral reversed will make an RCD non functional. I assumed, perhaps wrongly, that boats wired in polarized, UK style, use some other kind of RCD, sensitive to polarity.
But in areas with non polarized AC outlets (e.g. Schuko), polarity gets randomly reversed every time someone plugs in – still RCDs on extension leads and boats are in use and working.
Also, the ISO 13297, requires double pole CBs in non polarized systems for this very reason – both conductors should be treated as were they the active phase/line.

 

[VicS]

Luckily I did some testing before getting all grumpy and shouting at the boatyard that the power was off again...

RCD, can't be that old but wouldn't stay engaged so new one solved that. But the multimeter did show that there was voltage between neutral & earth with next to none between live & earth. Pretty certain it wasn't like that not so long ago and very possible that someone replugged in the euro plug "upside down" in the box. Rewired the ceeform so live is live once more.

So would the RCD not like that, could that be a possible cause of failure? Or maybe more likely getting damp in a rain shower?

Also, got given a couple of 240v mains LED drivers so thinking maybe wire one between the neutral and earth with a resistor and low power LED as an indicator to alert if the live/neutral isn't as it should be - any reason that wouldn't work? Maybe on the RCD out, though wonder if it would pull enough amps to trip the RCD if the L/N are the wrong way round..

Any thoughts?

TIA

An RCD is not "polarity" sensitive. It merely detects any imbalance between the line and neutral currents. If the difference in the current between the two conductors exceeds a certain value ( usually 30mA) the device will trip.

How RCDs operate is described clearly in this video

 

[lw395]

I can't see how a normal double pole RCBO can be sensitive to L and N being swapped?
There is no connection to E, so the potential of E relative to the L and N terminals can't be relevant?
I'm not aware of any RCDs intended to go in a typical UK consumer unit being anything other than double pole?

RCBOs, the MCB replacements which provide leakage tripping of a single circuit, e.g. lights in a house, are a different matter. They seem to only break the live and have an 'earth' connection, so could easily be sensitive to N/E potential difference.

 

[GHA]

OK, if bought in Portugal it is presumably two pole. The comment above states that getting live and neutral reversed will make an RCD non functional. I assumed, perhaps wrongly, that boats wired in polarized, UK style, use some other kind of RCD, sensitive to polarity.
But in areas with non polarized AC outlets (e.g. Schuko), polarity gets randomly reversed every time someone plugs in – still RCDs on extension leads and boats are in use and working.
Also, the ISO 13297, requires double pole CBs in non polarized systems for this very reason – both conductors should be treated as were they the active phase/line.

Thinking about this while grinding and welding this afternoon and it makes a bit more sense now - with just 2 AC terminals how could the RCD know which was which? So seems more likely the first one gave up due to moisture or just had enough.

As for using a mains LED driver as an indicator between neutral and earth........ maybe not a good idea, maybe someone tried it and if between live & earth it tripped the RCD. And the boatyard RCD as well..... :nonchalance:

Least they work

So questions answered thanks all and a little bit more learnt, be handy to find a neon to fit as an indicator, favourite little Portuguese backstreet switch n socket shop didn't have any.

 

[VicS]

Thinking about this while grinding and welding this afternoon and it makes a bit more sense now - with just 2 AC terminals how could the RCD know which was which? So seems more likely the first one gave up due to moisture or just had enough.

As for using a mains LED driver as an indicator between neutral and earth........ maybe not a good idea, maybe someone tried it and if between live & earth it tripped the RCD. And the boatyard RCD as well..... :nonchalance:

Least they work

So questions answered thanks all and a little bit more learnt, be handy to find a neon to fit as an indicator, favourite little Portuguese backstreet switch n socket shop didn't have any.

If you fit a neon as a "correct polarity" indicator between line and earth the earth connection must be made up-stream of the galvanic isolator ( if you have one) otherwise thr current flowing through the GI will put it in a conducting state and render it ineffective as a galvanic isolator. Not quite so much as a problem with an "incorrect polarity" indicator because it will not normally be illuminated but logic suggests both should be connected at the same point upstream of the GI

 

[greeny]

Thinking about this while grinding and welding this afternoon and it makes a bit more sense now - with just 2 AC terminals how could the RCD know which was which? So seems more likely the first one gave up due to moisture or just had enough.

As for using a mains LED driver as an indicator between neutral and earth........ maybe not a good idea, maybe someone tried it and if between live & earth it tripped the RCD. And the boatyard RCD as well..... :nonchalance:

Least they work

So questions answered thanks all and a little bit more learnt, be handy to find a neon to fit as an indicator, favourite little Portuguese backstreet switch n socket shop didn't have any.

Got one in my hand, just found it in the box in the garage not on the boat as I thought it might be. You at feedback Sunday?

 

[Lon nan Gruagach]

favourite little Portuguese backstreet switch n socket shop didn't have any.

Did they have any switches with neon indicators? You might find one in there.

 

[matthewriches]

Which RCD do you have fitted?

 

[PaulRainbow]

Correct polarity indicators are best made with LEDs, which are polarity sensitive. Connect a green one across the normal L and N, connect a red one the other way around. If the polarity is correct the green one is lit, if it's reversed the red one is lit.

 

[VicS]

Correct polarity indicators are best made with LEDs, which are polarity sensitive. Connect a green one across the normal L and N, connect a red one the other way around. If the polarity is correct the green one is lit, if it's reversed the red one is lit.

What you suggest is correct for DC circuits ( but DC has positive and negative rather than line and neutral)
However
ITYWF that GHA was referring to indicators to show correct or reversed line and neutral in an AC supply not the polarity of a DC supply. Neons ( and their associated series resistors ) can be connected between line and earth and between neutral and earth. When the so called "polarity" is correct the neon between L and E will be illuminated. If line and neutral in the supply are reversed the other neon, between what should be N and E, will be illuminated.

It is unfortunate, and confusing, that the term polarity is used in this context but it usually as and nobody seems to be able to suggest a better word word to distinguish between the line and neutral in AC circuits .
Strictly the term polarity refers to positive and negative of DC circuits

 

[matthewriches]

That's not going to work. Both LED's will remain on or might even strobe if mains quality is not great. Also, LED's used in your context would need rectifying.

A reliable indicator is wired across Live & Earth for "correct polarity" and Neutral & Earth for "wrong polarity". A neon is best used as it'll pull VERY little current. LED's after resistor loading, depending how it is done, may be close to the 30mA or even 5mA trip current of the RCD, fitted to the vessel or the shore post.

Correct polarity indicators are best made with LEDs, which are polarity sensitive. Connect a green one across the normal L and N, connect a red one the other way around. If the polarity is correct the green one is lit, if it's reversed the red one is lit.

 

[sailinglegend420]

Some boats will have a built in reverse polarity light, if not buy a cheap polarity checker in a DIY store. Keep it plugged into a spare AC outlet, this will also show earth faults. To correct for reverse polarity make up a short 16-16 amp male to female adaptor with the live and neutral wires reversed.

Beware - built-in polarity detector LEDs can show a reverse polarity when none exists. They can glow dimly which suggests there is a problem, but they are glowing dimly because there is only a small voltage between the Earth and neutral, not the full 220V you would get from reverse polarity. This small voltage of 5-10 volts AC is caused by poor or faulty pontoon wiring

The Neutral and Earth wire are joined at the main transformer supply so should be at the same potential. Under a heavy load there’s a voltage drop along the neutral wire, but because no current is flowing in the earth wire there is no voltage drop along the wire, so at the pontoon pedestal there is now a voltage difference between the neutral and the earth which is enough to dimly light the polarity detector; this should never be more than 5 volts. Above this Earth Leakage Breakers or RCDs may keep tripping, it depends on your AC installation. All pedestals on a pontoon on the same phase may show the same problem if the pedestals are connected in series, the ones closer to the transformer will have a lower Neutral/Earth voltage. Anything above 8 volts causes our RCD to trip.

In winter months the problem is much worse because the more power that is taken by other boats then the higher the earth/neutral voltage difference will be. Constant AC tripping could be a problem if heating or charging is left on whilst away from the boat, so try and arrange for someone to check that AC is always present.

Low AC voltage at the end of a long pontoon may stop appliances or the shorepower charger from working. Have a supply of long shorepower cables and try connecting to the head of the pontoon. This may bypass a boat that is taking an excessive amount of current to run heating or air-con units.

 

[rogerthebodger]

A neon is best used as it'll pull VERY little current.

As stated in post #4

Also when using a LED on a mains circuit you need to select a LED with a high reverse breakdown voltage.

 

[BabaYaga]

at the pontoon pedestal there is now a voltage difference between the neutral and the earth which is enough to dimly light the polarity detector; this should never be more than 5 volts. Above this Earth Leakage Breakers or RCDs may keep tripping, it depends on your AC installation. All pedestals on a pontoon on the same phase may show the same problem if the pedestals are connected in series, the ones closer to the transformer will have a lower Neutral/Earth voltage. Anything above 8 volts causes our RCD to trip.

RCD trips because somewhere current is leaking to earth. Seems to me that in your case the polarity light itself, as suggested in post #17, could be a good candidate.