Part P Insulation Testing of a Lighting Circuit Ask questions and find answers to many subjects relating to electrics and electrical work

[Lawrence]

I've added an additional light to an existing radial final circuit. In carrying out the insulation resitance test for Part P (I have an EAL level 2 certificate) do you need to remove ALL the light bulbs on the circuit being tested?

For switches with neons rather than dicsonnect the switch can you simply leave the switch open?

Thanks

[sparx]

Hi, Best way for existing circuit is to disconnect L, & N. @ board and temp join together as one meter connection & earth as other one you won't damage or be confused by neons etc & with all lamps in & switches 'on' will test whole circuit for I.R. on test sheet if it asks for L -N put N/V ie
Not Verifiable, this is quite acceptable as it's not usually possible to disconnect every thing & could lead to disturbing good circuit components.
Regards SPARX

[Lawrence]

Thanks Sparx.
Am I correct in understanding that I should disconnect the L from the MCB & N from the N block and then join L & N together to create a circuit via a junction block?

I appreciate your help here.

[sparx]

YUP! if you draw a simple circuit you will see that by doing so any thing (neon, bell transformer etc) connected across circuit will be at same potential so whacking 500volts D.C. between them and earth as your Insulation tester does will only try to stress the insulation of conductors and not hurt delicate components.
You can do this with power circuits also BUT you may still get low I.R. reading if things with mains suppression filters fitted are plugged in (motors in D/Wash.-wash m/c - fridge- P.C. multi skts etc) as they are meant to have high resistance @ 50 Hz, but low at dc. however usually able to un plug first, B-W SPARX