Any Ideas Working This Out ?

[300TDI]

Ok

Been called to look at an installation - on the way home job

Customer has a three phase fuse board - been there years, but looks ok

About 6 months ago they had a new room built, and a new consumer unit was installed to supply this ( not by me )

The consumer unit is fed from the three phase board, and has a main rcd switch, mcbs feeding various circuits - shower, hand dryers, lights, and an rcbo feeding sockets ( a bit strange been as the main switch is a 30ma rcd aswell ? )

The problem is that when he switches off a floor standing fan ( at the socket ) the rcd main switch trips, but the socket is fed from the fuseboard, not the consumer unit.

Also when the sangamo timer switches the blow heating system on, that also trips the rcd, and the heating circuit is fed from the fuseboard aswell, not the consumer unit.

Looks like a bit of testing to do, but i cant understand why the rcd main switch is being tripped when the circuits causing this are fed from the main fuseboard, as the rcd seems to be tripping as if something is being sent down the tails to the rcd main switch on the supply side - not the outgoing side.

What do you make of this ??

 

[paul b b]

is it a TT?

 

[Andy™]

borrowed or misplaced neutral?

 

[300TDI]

[quote name='Andy

 

[300TDI]

is it a TT?

Its a TNS

 

[batty]

Its a TNS

Bad workmanship having 30mA Rcd as main switch and with TNS should not need it. Could be a fault on one of circuits or a bit of leakage on a lot of circuits causing nuisance tripping. I would test RCD first.

batty

 

[Andy™]

Bad workmanship having 30mA Rcd as main switch and with TNS should not need it. Could be a fault on one of circuits or a bit of leakage on a lot of circuits causing nuisance tripping. I would test RCD first.batty

since its a TPN board, it was probably done to save money on many RCBO's

 

[batty]

[quote name='Andy

 

[300TDI]

The tp&n board has been there years, before rcds were needed

Its the consumer unit that has the rcd main switch ( and an rcbo ? ), this is new, what i cant understand that its not the outgoing circuits of the consumer unit that cause it to trip

Its the existing circuits from the existing tp&n board,( the origin of supply to th consumer unit ) which leads me to believe that the rcd main switch is being tripped from the supply side, anyone ever heard of this ?

 

[batty]

The tp&n board has been there years, before rcds were neededIts the consumer unit that has the rcd main switch ( and an rcbo ? ), this is new, what i cant understand that its not the outgoing circuits of the consumer unit that cause it to trip

Its the existing circuits from the existing tp&n board,( the origin of supply to th consumer unit ) which leads me to believe that the rcd main switch is being tripped from the supply side, anyone ever heard of this ?

Can't see that personally unless you have a borrowed neutral.