quick question on RCD split consumer unit

[ZETEC153]

hi

today i was changing the sockets in the kitchen and running some new cable in.

i isolated the circuit on the MCB and cgecked it was dead before starting. Noticed about 0.8 - 1.0 volt on the live conductor. Didnt think too much of it untill i went outside to get something from the garage and noticed the RCD which protects the shower, sockets, and kitchen sockets had tripped.

After a bit of head scratching i reset the trip and it was fine. Then i tried something. I checked there was deffo no voltage on the live conductor, and then touched the neutral to the earth. This blew the RCD straight away.

This also happened when i did the same to the live. No voltage on the conductor but it tripped the RCD. no danger of flashes or nig bangs as no voltage present apart from the 1.0 volt or so.

is this a normal thing to happen??

cheers

george

 

[Spark123]

Yep, it only takes a few mA to flow between N&E to trip an RCD. Even with the MCB off there may be enough potential between N&E for enough current to flow to trip an RCD.
Should also note that adding to a socket circuit in a kitchen is a notifiable activity under part p.

 

[ZETEC153]

Yep, it only takes a few mA to flow between N&E to trip an RCD. Even with the MCB off there may be enough potential between N&E for enough current to flow to trip an RCD.
Should also note that adding to a socket circuit in a kitchen is a notifiable activity under part p.

cheers Spark123

that put my mind at rest a bit!! its only 30mA isnt it?? so not much at all really!!

does it cost to notify under part p?? i didnt add a socket, just replaced the existing and relpaced the cable.

cheers

george

 

[securespark]

Was the cable damaged by fire flood impact or vermin?

 

[ZETEC153]

looked like it had been beashed about a bit. had chunks of the outer grey PVC missing and just looked like it had been abused. it is just clipped along the kitchen wall behind the units.

does that have an impact on whether it needs registering?? would it be classed as a minor works??

cheers

george

 

[Lectrician]

With the MCB off, the neutral is still connected.

The returning neutral current from other circuits can take a route earth when you short N and E, and if 30mA does, your RCD will trip. Usually with no load on any of the other circuits this will not happen.

Touch the isolated live to earth can also cause the RCD to operate if you have loads on your isolated circuit on - The returning neutral current can flow down the neutral and then the live, through the element/appliance and then to earth.