VicS
Well-Known Member
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RCD disconnects the system from the mains in the event of >30ma current flowing in the earth lead, due to a fault or leakage problem
[/ QUOTE ] Not quite right. That's how I think you will find an earth leakage circuit breaker (elcb) works but if I understand correctly they are not now allowed on domestic installations. The RCDs that we do use sense any difference between the current flowing in the live and neutral (supply and return, or what ever the latest jargon is) That difference is due to current leakage to earth but is not necessarily via the earth conductor, it can be through you and the wet ground you are standing on. That's how they save lives.
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I cheated and fitted four low current diodes in my boat (they will only need to carry a >30mA spike for a short while
[/ QUOTE ] I think you may be a little misguided here too. I have had a couple RCDs fail but they did fail safe, they simply failed to trip when required to do so. If the RCDs fail and therefore do not trip in the event of a live to earth fault then it is probable your puny low current diodes will blow but the fuse will not blow (or the mcb open). That will leave you with an open circuit in your shorepower earth connection and a potentially dangerous situation on board. I concede that both on-board and shore-side RCDs will have to fail to operate but I would not depend upon the shore-side one. I would urge others not to adopt your suggestion regarding low current diodes. To ensure total safety, in so far as mains electricity can ever be safe, the galvanic isolator must be able to handle a current in excess of the fuse or mcb rating.
RCD disconnects the system from the mains in the event of >30ma current flowing in the earth lead, due to a fault or leakage problem
[/ QUOTE ] Not quite right. That's how I think you will find an earth leakage circuit breaker (elcb) works but if I understand correctly they are not now allowed on domestic installations. The RCDs that we do use sense any difference between the current flowing in the live and neutral (supply and return, or what ever the latest jargon is) That difference is due to current leakage to earth but is not necessarily via the earth conductor, it can be through you and the wet ground you are standing on. That's how they save lives.
[ QUOTE ]
I cheated and fitted four low current diodes in my boat (they will only need to carry a >30mA spike for a short while
[/ QUOTE ] I think you may be a little misguided here too. I have had a couple RCDs fail but they did fail safe, they simply failed to trip when required to do so. If the RCDs fail and therefore do not trip in the event of a live to earth fault then it is probable your puny low current diodes will blow but the fuse will not blow (or the mcb open). That will leave you with an open circuit in your shorepower earth connection and a potentially dangerous situation on board. I concede that both on-board and shore-side RCDs will have to fail to operate but I would not depend upon the shore-side one. I would urge others not to adopt your suggestion regarding low current diodes. To ensure total safety, in so far as mains electricity can ever be safe, the galvanic isolator must be able to handle a current in excess of the fuse or mcb rating.
