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 .

 

[Strima]

Possibly a poor neutral connection on the supply side of the installation.

 

[PEG]

Hi,have you done any continuity testing,between the old and new cables? ....coz you have a link...

 

[Munders]

Both main earths were still connected.
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Basically, I was in a mad rush to get the lights on as I was loosing the daylight. I got them on, pulled the tails from the old supply and left the main earth so I could crack on with the sockets. ( needed to get the sockets on before owners came back ). Then whilst cutting off an old socket the RCBO on the downstairs lights only tripped. It was because the old main earth was still in at the board but like I say from my initial post, I was just curious why only the one RCBO tripped as everything else stayed on.

 

[Pretty Mouth]

Both main earths were still connected.
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Basically, I was in a mad rush to get the lights on as I was loosing the daylight. I got them on, pulled the tails from the old supply and left the main earth so I could crack on with the sockets. ( needed to get the sockets on before owners came back ). Then whilst cutting off an old socket the RCBO on the downstairs lights only tripped. It was because the old main earth was still in at the board but like I say from my initial post, I was just curious why only the one RCBO tripped as everything else stayed on.

Hi Munders, please clarify:
So far you have installed a new CU
disconnected the tails from the old CU and connected them to the new CU
Moved some, but not all, existing circuits over to the new CU
Not rewired any ciruits
is this correct?

 

[Munders]

Brand new installation, all new wiring and new board. Completely separate from old wiring. Obviously apart from the main earth I mentioned