Lighting circuit fault

[mikel]

I've been asked to do a consumer unit change, I thought before I start to change it I'd do some testing. Everything was going fine till I got to the lighting circuit for half the house. (There are 2 lighting circuits one for one half the house both up and downstairs and another for the other half). The r1 and r2 measurements were ok max reading 1.6 ohms. However when I came to do insulation resistance I got the following

Line to neutral 3.6 Mohms

Line to earth 1.8 Mohms

neutral to earth 2.49 Mohms

Anyone got any ideas what may be causing these readings, think it needs sorting before I even think of doing the consumer unit change

 

[RussellR]

One option is a damaged cable maybe look for pin holes etc, on drops to switches and wall ligh

 

[Robin Spark]

Well all of those readings are gonna comply with Regs min insulation resitance values of 1megohm and they wont be low enough to trip rcd either.

Is it pvc T&E and approx age?

Any sign of damp on walls or ceiling? Did the IR values on test remain steady or did they rise?

Did you look at any outside light fittings?

 

[mikel]

No outside light fittings on the circuit. Readings remain steady, When I split the circuit down all but 2 sections give readings of >299 Mohms the other 2 sections give readings of 98Mohms and 19Mohms respectively. Put all the circuit together (split it at each celing rose and I'm bck to my original readings. Have inspected all wiring at the ceiling roses and they seem fine. don't know where to go with it, can't get access to the sections of wiring that give low results. The house has been unoccupied for about 4 months but no obvious signs of damp.

 

[RussellR]

are they runs through the ceiling ?

 

[mjse]

have you tried testing the switch wires on the 2 parts that are down?

maybe easier to access

 

[cheggers]

have you removed all lamps

is there some thing still connected IE TV booster

failing all that do the cu change your reading are acceptable nothing to worry about

 

[matt.leung]

are there any low voltage transformers still connected?