RCD - sensitive to L/N swapped?

[lw395]

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.

Most LEDs have very low reverse voltage ratings, 5V is quite typical.
It's normal to use a few components around them for a mains indicator.
If you buy a packaged 'Mains LED indicator' it might be capacitively coupled and not work with DC.

 

[rogerthebodger]

Yes that was the point I was trying to make, not very well

 

[sailinglegend420]

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.

If there's 8v between neutral and earth then a current will flow down the earth wire - Ohms Law.

My polarity is a standard fitting on my boat so would not be installed if it could take the 30mA needed to trip the standard fitting breaker.

 

[BabaYaga]

If there's 8v between neutral and earth then a current will flow down the earth wire - Ohms Law.

My polarity is a standard fitting on my boat so would not be installed if it could take the 30mA needed to trip the standard fitting breaker.

I have no problem understanding that such a voltage difference could cause a current to flow and the light to glow.
Less clear to me is why the RCD would trip, if the polarity light is not the cause. Voltage drop should affect L and N alike, so why the unbalance?

 

[Lon nan Gruagach]

If there's 8v between neutral and earth then a current will flow down the earth wire - Ohms Law.

My polarity is a standard fitting on my boat so would not be installed if it could take the 30mA needed to trip the standard fitting breaker.

Only if there is a neutral - earth connection [edit add]on your boat[/edit], which is a fault and should trip.

If it is your polarity indicator then a reversed supply should always trip your RCD, since in that case instead of 8Vac across the neon there would be 240Vac and thus higher current.
I think you have a fault.

 

[sailinglegend420]

.....Voltage drop should affect L and N alike, so why the unbalance?

.....I think you have a fault.

Let me try and explain again!

If there is a large current being drawn on a pontoon and the cables and/or connectors are poor quality then a voltage drop - say 8v - will occur on both Live and Neutral cables. There will never be a voltage drop on the earth wire because there is no current - unless there is a fault.

At the transformer end the earth and neutral are joined - so at the end of the Neutral wire there is now an 8v AC difference between Neutral and Earth. Polarity detectors light when there is a voltage difference between Neutral and Earth, and they can glow bright enough even with this low voltage to suggest a reverse polarity situation.

I hope this fully clarifies this complicated electrickey situation.

 

[Lon nan Gruagach]

Let me try and explain again!

If there is a large current being drawn on a pontoon and the cables and/or connectors are poor quality then a voltage drop - say 8v - will occur on both Live and Neutral cables. There will never be a voltage drop on the earth wire because there is no current - unless there is a fault.

At the transformer end the earth and neutral are joined - so at the end of the Neutral wire there is now an 8v AC difference between Neutral and Earth. Polarity detectors light when there is a voltage difference between Neutral and Earth, and they can glow bright enough even with this low voltage to suggest a reverse polarity situation.

I hope this fully clarifies this complicated electrickey situation.

Let me explain again. If your RCD trips, you have a fault.

 

[Lon nan Gruagach]

duplicate

 

[sailinglegend420]

Let me explain again. If your RCD trips, you have a fault.

duplicate

You initially said - I think you have a fault - now you know I have a fault - WHY?

You can't keep posting the same thing without explaining where the error is in my detailed response to you. ​Most of your other posts are in the Lounge - you are not known for your knowledge on electrikery.There have been 710 views of this thread - they would all probably be interested in the correct information for this complex problem that I have seen for the last 10 years in the Med. This only occurs on my boat in old marinas with old or faulty wiring.

 

[BabaYaga]

Let me try and explain again!

If there is a large current being drawn on a pontoon and the cables and/or connectors are poor quality then a voltage drop - say 8v - will occur on both Live and Neutral cables. There will never be a voltage drop on the earth wire because there is no current - unless there is a fault.

At the transformer end the earth and neutral are joined - so at the end of the Neutral wire there is now an 8v AC difference between Neutral and Earth. Polarity detectors light when there is a voltage difference between Neutral and Earth, and they can glow bright enough even with this low voltage to suggest a reverse polarity situation.

I hope this fully clarifies this complicated electrickey situation.

Thank you for your explanation. Easy to understand how this might happen. The same issue is also clarified e.g. here:
https://www.bluesea.com/resources/85
However, it is still not obvious why this situation would trip the RCD.
NB I'm not saying that it did not, just curious to understand how.

 

[syTaika]

If everything is OK, swapping L and N will not trip the RCD. If it does, then the reason might be that there is an insulation fault in one of the wires. If this wire is N, the voltage difference to ground is low and the resulting leakage current is low as well, and the RCD will not trip. However, if this wire is connected to L, the leakage current from this wire to ground will be much higher and the RCD will trip. I had this situation once with my damaged extension cord.

 

[Lon nan Gruagach]

You initially said - I think you have a fault - now you know I have a fault - WHY?

You can't keep posting the same thing without explaining where the error is in my detailed response to you. ​Most of your other posts are in the Lounge - you are not known for your knowledge on electrikery.There have been 710 views of this thread - they would all probably be interested in the correct information for this complex problem that I have seen for the last 10 years in the Med. This only occurs on my boat in old marinas with old or faulty wiring.

There are few, and only significantly exotic ways, to trigger a RCD without a fault condition. One being a massive load on the same sub-station output energising at the right part of the mains cycle. It needs to be large enough to effectively push a d.c. spike through your RCD such that capacitative coupling to ground causes a fault current.
It is safe to say that such occurrences are rare are not likely to be as repeatable as your trip. So, the only other ways a RCD might trip is if there is no wiring/equipment fault, but it is faulty or there is a wiring/equipment fault. Either way, you have a fault.

Now, IF it is the reverse polarity indicator that is causing the trip then it is not fit for purpose (a fault!) Why do I say it is not fit for purpose? If 8Vac causes it to trip the RCD then if you do connect to a reverse polarity supply it will have ~ 240Vac across it. This will certainly cause it to trip the RCD instead of indicating reverse polarity. It is exceedingly bad practice for an installation to falsely identify a fault.
As has been suggested up-thread,cheap plug-in mains testers are a good option for a reverse polarity indicator, They overturn do much more, including showing correct polarity, and earth continuity (although consideration of galvanic isolators plays a significant part in where you connect or how you use such a device).


Earlier you assert that more than 5Vac Neutral to Earth is evidence of poor or faulty pontoon wiring. In a marina I would expect phase load imbalance to frequently cause N-E to exceed 5Vac. 4Vac is common in towns where you expect far tighter balancing.

RCDs are not phase sensitive, the standard construction of L and N passing through a sense coil cannot be phase sensitive so high N-E voltages cannot cause a trip unless you have a N-E fault.

Regardless of what you think you know of my knowledge of "electrikery" [sic], if your RCD trips, you have a fault.

 

[lw395]

One of the amusingly obscure ways an RCD can trip is if you have L and N swapped, resulting in single pole switching being only on the N side. If you combine this with a lot of capacitance to ground (perhaps from filters) or inductive coupling, it's possible to get tripping.
SO IMHO, it is worth taking care with L/N swapping, or ensuring everything is double pole switched, double insulated etc.

 

[sailinglegend420]

....However, it is still not obvious why this situation would trip the RCD.....

Thanks for the link - diagrams certainly help to explain the situation.

.....Regardless of what you think you know of my knowledge of "electrikery" [sic], if your RCD trips, you have a fault.

Many thanks for your very detailed response.

I suspect that my 'fault' may be my Victron Multiplus Charger/Inverter that is wired in series with the AC mains and senses the earth/neutral 8v imbalance and is not happy.

I welcome any other suggestions.

 

[lw395]

..

I welcome any other suggestions.

The obvious 'other suggestion' is that your boat has faulty N-E or L-E insulation.
It would be prudent to rule that out ASAP.

 

[matthewriches]

Please explain??

Victron Multiplus Charger/Inverter that is wired in series with the AC mains

 

[VicS]

. my Victron Multiplus Charger/Inverter that is wired in series with the AC mains

Please explain??

I would have thought that was fairly obvious if you look at the installation instructions

Slightly simplified diagram:

 

[matthewriches]

Vic, you are an intelligent bloke, but your flippant comment does you no favours this time.

You'll understand that installing a Victron inverter as per your diagram is NOT actually wired in series.

Nominal UK voltage is 230V, inverter output say 230V, so if a series connection, what would the sum output voltage be??

Furthermore the Multiplus has all kinds of features, such as the ability to "boost current" to support weak shore power supplies, act as an uninterrupted power supply, etc.... of which, are not afforded by a series circuit; are they?

I would have thought that was fairly obvious if you look at the installation instructions

Slightly simplified diagram:

 

[sailinglegend420]

....You'll understand that installing a Victron inverter as per your diagram is NOT actually wired in series....

You need to appreciate the the Victron Multiplus is wired exactly as Vic describes. It synchronises itself to the incoming AC phase so that its output is the same so when needed it takes extra power from the battery - eg. if the shore power can only supply 16 amps and the boat demands 20 amps.

 

[VicS]

Vic, you are an intelligent bloke, but your flippant comment does you no favours this time.

You'll understand that installing a Victron inverter as per your diagram is NOT actually wired in series.

Nominal UK voltage is 230V, inverter output say 230V, so if a series connection, what would the sum output voltage be??

Furthermore the Multiplus has all kinds of features, such as the ability to "boost current" to support weak shore power supplies, act as an uninterrupted power supply, etc.... of which, are not afforded by a series circuit; are they?

The aim was to explain, or at least help you understand, why sailinglegend described it as "wired in series", but failed obviously

SHOREPOWER SUPPLY - - - - MULTIPLUS - - - - BOAT AC SYSTEM​

The three items are "in series" , like trucks in a railway train, one after the other

Electrical or electronic components are said to be "in series " when a common current flows through them.
When the Multiplus is operating in shorepower mode it could be argued that a common current flows in the shorepower supply, the Multplus and the boat AC circuit.