false meter readings or residual reading?

[josh1e]

i have a fluke multimeter. I use it for testing anything from pcb repairs to 240vac mains in domestic only locations.

I'm a diyer & use it mostly after i've killed the circuit @ the MCB i'm working on & want to ensure those wires were correctly connected to it. (ie when checking for dead / live cables / light fittings etc.)

I've seen the musings on here at diyer's using multi meters & thats not the reply i am after, i've read it already - thank you

I have often found surplus cables which were disconnected prior to any work i've done. old shower cables for example which have since been replaced, disused lighting circuits etc. on some occaisons these are taped up, other times just bare wires or a terminal block sticking into the loft insulation...

Sometimes on my meter these give a very low reading, only mv usually. is there a reason for this? is it down to the meter? a 10m length of cable picking up interference which is registering? sorry if that sounds daft. I haven't looked for these cables within the fusebox as i am satisfied that they are not live, nor are they anything i have laid / moved / tampered with. but it has bugged me why i get a reading...

also under the regs, i thought wiring was supposed to be identifyable after installation? doesn't this include wiring which has been disconnected but left in situ? or did i misunderstand?

thanks

 

[hairyben]

A voltage can be "induced" across two cables running in parallel due to the magnetic field of mains cables. This is why telecoms, TV etc must be kept away.

 

[RF Lighting]

It can be caused by capacitive coupling from another cable.

If you were to use an older style analogue meter, or connect a load across your test probes (such as a 60W lamp) you should see no voltage registering on your meter.

It is the impedence of your multi meter which allows such a small amount of current to register on the display.