Lighting circuit

ac/dc · Nov 9, 2012

EVENING ALL

HAVING BEEN AROUND THIS OLD BLOCK OF FLATS FOR SOME INSPECTION
I CAME ACROSS A LIGHTING CIRCUIT ON THE HALLWAY (5 FLOORS ) WITH NO CPC , BUT NO SWITCHES.
WIRED WITH 2.5mm SINGLE CORE ON METAL CONDUIT AND RCBO PROTECTED
STAIRCASE LIGHTING CIRCUIT ALSO WITH NO CPC AND ON BORROWED NEUTRAL WIRED WITH 2.5 mm ON 10 A MCB
(TRYING TO CHANGE FROM MCB TO RCBO)
I COULDN'T FIND WHERE IS BOROWED FROM (NOT FROM HALLWAY LIGHTING CIRCUIT).
THE 13 WAY RCD - COMMUNAL DB IS ON THE BASEMENT AND WIRES IN THE METAL TRUNKING ARE A SPIDER WEB GOING IN AND OUT
OF THE TIMERS ALL SINGLE CORE.

PLEASE, ANY FAST WAY OF FINDING THE BORROWED NEUTRAL OR DO I HAVE TO DISCONN. ALL THE WIRES AT THE D.B.

THX . IN ADV.

telectrix · Nov 9, 2012

if the circuit is singles in metal conduit, then the conduit is probably the cpc. if you need to find the borrowed N, then it's a case of disconnecting and testing till you find it. no quick fix here, mate.

ackbarthestar · Nov 10, 2012

I assume that the shared neutral is across the hallway and staircase lights?
It would only be 'borrowed' if the parts of the lighting circuit are connected across two different breakers. Placed in one breaker or RCBO and the lights should be ok. that is as long as the In rating is able to cope with the load.

ac/dc · Nov 12, 2012

HI
WENT THIS MORNING TO THIS PROPERTY AGAIN AND THERE IS NO CPC (EARTH) ON THE LIGHTING CIRCUIT.
2.5 mm SINGLE CORE LINE & N. WIRED IN METAL CONDUIT BUT THERE IS NO CONTINUITY.
RCBO -16A
PLEASE, WHAT WOULD YOU WRITE ON THE CERT. IN TERMS OF ZS , RCBO DISCNN. TIME, ETC.

THX .IN ADV.

ackbarthestar · Nov 12, 2012

ac/dc said:
HI
WENT THIS MORNING TO THIS PROPERTY AGAIN AND THERE IS NO CPC (EARTH) ON THE LIGHTING CIRCUIT.
2.5 mm SINGLE CORE LINE & N. WIRED IN METAL CONDUIT BUT THERE IS NO CONTINUITY.
RCBO -16A
PLEASE, WHAT WOULD YOU WRITE ON THE CERT. IN TERMS OF ZS , RCBO DISCNN. TIME, ETC.

THX .IN ADV.

The cpc continuity is likely to have existed once upon a time, but after a period of time where there have been additions, alterations, loosened joints and possible corrosion the continuity is no longer available.
As it is a communal, public area and the switches and lights have exposed conductive parts then it is a failed circuit and should be coded appropriately.
You cannot rely on the RCBO to provide protection where there isn't a suitable earth fault path. (531.2.5) So IMO it would be C1