RCBO trip.

[Munders]

Got a large rewire ongoing at the minute. Owner wants to use current sockets alongside the new board as he’s living in one part of the house whilst the builders are in. Today the old supply was disconnected and whilst cutting through an old cable not connected to any of my new legs the RCBO tripped on the new lights. I tried it several times and same result. It’s not a problem, I’m just curious why. The only thing I can think of is that both the old main earth and new were still connected at the meter. If that is the case then why only the lights and nothing else.

 

[Andy-1960]

What’s the earthing system to the property?

 

[buzzlightyear]

would a dual rcd in place and on the rcd that cables that been cut ,me I would only put a
a temp supply for the builders only ,has for the owner that lives their then he would use it has well.

 

[Munders]

like I say it’s more curiosity than a problem. It’s a tns system. I have to do it bit by bit as there’s a large family living in it and they need power. The only issue is as I go round cutting off the old sockets and lights my new rcbos are tripping. More of a pain as a problem as once it’s all cut out it won’t be an issue.

 

[buzzlightyear]

The only issue is as I go round cutting off the old sockets and lights my new rcbos are tripping

is the old cable still on the new consumer unit and you are cutting them .

 

[Munders]

is the old cable still on the new consumer unit and you are cutting them .

It is. The only link is the main earth. I gues if that’s disconnected my issue will go away. Like I say, it was more curiously

 

[Baddegg]

If a new adequately sized main earth is installed (who installed it?) I’d remove the old and see what happens.....can’t get my head round how it would cause the rcbo to trip though but I’ll hang around cos there a lot wiser people than me on here and I’m as curious as you now

 

[buzzlightyear]

The only link is the main earth. I gues if that’s disconnected my issue will go away

the system is a tns and you want to remove it are you mad .so where would the earth path go then .

 

[Baddegg]

the system is a tns and you want to remove it are you mad .

I read it as a new earth has been installed and he wants to remove the old?

 

[buzzlightyear]

I read it as a new earth has been installed

must be a leakage some where .
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Today the old supply was disconnected

both the old main earth and new were still connected at the meter

so the begging question why are there two main earths or am I reading this wrong .