Possible borrowed neutral ring mains

[TJC1]

Done a fuse board change on a propery, hasnt been touch since early 60s at a guess.

There is 2 ring mains, which i had split over the the 2 rcds. Each time i swithched on one, the other RCD tripped out, and vise versa.

Have no end to end on one ring main, and end to end on Line & Earth but not the neutral on the other ring.

To get it going for the weekend i put both rings on one RCD, but still tripped out.

Does this sound like a borrowed neutral problem, or a inter crossed ring main?

 

[The Ghost]

Yep usually is. Crossed neutrals not necessarily the rings but another circuit neutral. I hate it when that happens especially with singles circuits.

 

[Pete999]

So no testing beforehand then?

 

[Andy78]

Done a fuse board change on a propery, hasnt been touch since early 60s at a guess.

There is 2 ring mains, which i had split over the the 2 rcds. Each time i swithched on one, the other RCD tripped out, and vise versa.

Have no end to end on one ring main, and end to end on Line & Earth but not the neutral on the other ring.

To get it going for the weekend i put both rings on one RCD, but still tripped out.

Does this sound like a borrowed neutral problem, or a inter crossed ring main?

So then only one ring, which is faulty, which you energised anyway ?

 

[Jamchiv01]

Hello, Yes this would indicate a cross-connection between the 2 RCDs

If it only trips when you turn the MCB on, it indicates the line conductor that has been cross-linked.
If it trips instantly when you turn the RCD on, this would indicate a cross linked neutral.

A popular cause of this is lighting circuits, someone decides they want a new light and borrow a neutral from the nearest place and a live from some other circuit.

I presume you have Tested the insulation on both ring circuits and they checked out okay, if this is the case then my advice would be to remove all neutrals and earths from the board.

While the circuits are dead, IR test between all the cables, to ensure there is no connection between any cables there shouldn't be.

If there is, use the half split method to test and locate the connection.

Doing this should locate the fault efficiently so it can be rectified.

Hope this helps.

 

[TJC1]

So no testing beforehand then?

Obviously not... Just after some advice.

 

[Jamchiv01]

http://www.----------------------------/mediafile/100423440/Best-Practice-Guide-1-Issue-3-.pdf

Read 6.2 Planned change (6.2.1, 6.2.2)

 

[sparksburnout]

Obviously not... Just after some advice.

Well, I have to be very careful here, as I can come over as a bit of a negative old git. However, it does say in your profile that you are an "electrical contractor". So, my advice would be, next time, do what you are supposed to do, as an "electrical contractor", and don't get your self into this mess, as you obviously have no idea what the problem might be. Are you going to give your customer a decent discount for not doing a particularly good job, so far? Why didn't you do any testing? What testing are you going to now do, given the problem?? I would guess that you have probably made a very basic error when you put everything back together, which will now be a bit more tricky to resolve.Oh, and BTW, what is an "inter crossed ring main", when it is at home??

 

[Octopus]

Are you 100% sure you have the correct neutrals in the correct bars?

 

[7029 dave]

Are you 100% sure you have the correct neutrals in the correct bars?

He does not even have end to end N on any of the circuits. But still energised both on RFC.?On one circuit.

 

[7029 dave]

Well, I have to be very careful here, as I can come over as a bit of a negative old git. However, it does say in your profile that you are an "electrical contractor". So, my advice would be, next time, do what you are supposed to do, as an "electrical contractor", and don't get your self into this mess, as you obviously have no idea what the problem might be. Are you going to give your customer a decent discount for not doing a particularly good job, so far? Why didn't you do any testing? What testing are you going to now do, given the problem?? I would guess that you have probably made a very basic error when you put everything back together, which will now be a bit more tricky to resolve.Oh, and BTW, what is an "inter crossed ring main", when it is at home??

Think he is saying, maybe interconnection between both circuits.?

 

[hightower]

Well well well we're feeling the Christmas spirit in here today. Surely given the OPs responses the only reply he should be getting is 'come back when you have a set of test results'?

 

[Octopus]

He does not even have end to end N on any of the circuits. But still energised both on RFC.?On one circuit.

Time for a piece of paper, a MFT and some logical thinking then with some very basic tests....

If both circuits are tripping, I wonder how the homeowner is coping?

 

[andyb]

It's more likely to be an IR fault, was this tested beforehand?

 

[Jamchiv01]

Well well well we're feeling the Christmas spirit in here today. Surely given the OPs responses the only reply he should be getting is 'come back when you have a set of test results'?

The way I think of it is we help this guy now, and someone looking for the same issue in the future finds his answer.