5-core

[notb665]

I had occasion to wire up my new underfloor heating control centre. I had to extend the cables from the distributor pumps, which are 5 core. Their colours are green/yellow, brown, blue, grey and orange.

The cable I bought to extend it has the colours green/yellow, brown, blue, black and black.

Wanting to distinguish which black was which, and not having a tester , I connected one of the black wires to a live from a light switch. *All* the 5 wires were live, even though four of them were not connected.

So after pondering for a while, and thinking that a return is needed, I wired up a light bulb using a 3A plug socket and connecting strips using the 2 black wires and made safe the ends of the other wires. From this is could obviously test which was the phase and which one was the return and marked them accordingly.

My question is: Upon connecting only one of the black wires to a live, why did all the others become live? I noticed this once before when I was installing a fused switched spur and lost track of which end was which.

 

[breezer]

how do you know they were live?

let me guess, you had a "tester screwdriver" / volt stick or similar.

bin it

 

[brown-nought]

Wanting to distinguish which black was which, and not having a tester , I connected one of the black wires to a live from a light switch.

Please buy a test meter you can get them for under £20. Testing at mains voltages kills.

 

[notb665]

Upon connecting only one of the black wires to a live, why did all the others become live?

 

[comms]

If you were using an illuminating test screwdriver to test for power, it would have been picking up the source of live power from the one cable you had connected up to the light switch, even if you had it touching one of the unconnected cables, this would be because the live cable is within a close proximity to the test screwdriver.
The test screwdriver picks up the electric field current that is given off by all conductors with a current passing down them, this will illuminate the screwdriver led.
Hope thats not to confusing.

 

[notb665]

Thank you - that's what I thought.

The reason why I used one of those (yes, I know they're crappy) screwdrivers was because I didn't have a proper tester, and couldn't see one from Screwfix.

Perhaps someone would like to recommend one to me?

 

[brown-nought]

Screwfix (when they are up!!) do a cheap clamp meter for £20. The clamps useful to hang it off your belt. Search for part no 13489.

 

[notb665]

Thanks.

I would just like to point out that I did not put the word 'rubishy' in my previous post. I put a very mild word rhyming with 'caddy'. If I had wanted to put 'rubbishy', I would of course put 'rubbishy', not 'rubishy'!

I pride myself on my impekkabul Inglish innit.

 

[Paul_C]

Even when using a test meter you can read a voltage on other wires within a cable which are not connected. This is especially so with almost any digital meter which has a high impedance input. It's caused by the capacitance between the conductors in the cable.