Overlapping Earth fault Paths

[Jim2287]

Is it possible for overlapping earth fault paths to trip RCDs ?

Two houses next door to each other, both TT systems

One house has a fault which passes to earth, and it trips an RCD in the 'other' house ?


Possible or not ? if yes, could you explain how it works?

Thanks

 

[JohnD]

I believe it happens (not just on TT) because they have Main Bonding to the gas and water pipes and the current travels down one and up the other.

 

[Jim2287]

Im sure ive seen someone say something about it before here, but i couldnt find it when i looked

I used TT because its one with most likely to have RCD on to trip, but any info for service bonds causing it to happen would also be great

 

[Adam_151]

It is possible, but not I belive without the RCD in the house that the fault occurs in also tripping (or RCD only not tripping because its broken I suppose)

I recall a post came up on the IEE forum about a guy installing at a remote-ish supply (mobile transmitter rings a bell, but could as easily be a remote house) and everytime he put his ELFI tester between the incomming supply and the MET he tripped the RCD at a nearby TT farm.

The answer the forum came up with, is that the fault current (or test current in this case) being driven through the ground and through the suppliers neutral earth bond, this may be of a reasonable impedance and may have even corroded beyond its allowed bounds over the years, there will be a potential across this ground stake equal to V=IR, now if the farm has a neutral earth interconnection of some end (either short or through an imedance) a difference in potential between N and Earth will cause a current flow between them and if the RCD is quite near to tripping...

 

[ricicle]

This used to happen with the old voltage operated trips but I've never heard of it with current operated ones

 

[sm1thson]

//www.diynot.com/forums/viewtopic.php?t=53582

link DIYnot post about a neighbours lawnmower tripping RCD[/url] on this post it did seam it was an old RCD.

 

[JohnD]

It was fairly old, but still current operated.

But it seemed to trip in 17mS which is unusually fast (can't see what the test current was) so it might have been faulty or had a slight general leakage overhead. Don't think we heard back from that guy, so perhaps the new RCD fixed his prob.

 

[Jim2287]

OK so it used to happen to Voltage Monitoring 'RCDs' and its possible that it could happen to current RCDs if the RCD is close to tripping, it just tips it over the edge

Is there no other web pages explaining this, that any one knows of ? or is it that uncommon its not experimented with

 

[plugwash]

its one of those things, if an installation is in good condition then it really shouldn't be possible to trip its RCD from outside. Sometimes however it seems to happen anyway for no obvious reason.