Electrical question : Lighting help

[digitalfm]

Hi, I'm building a cinema room and have just fitted new lights.

In the light fitting I have the usual 1 black 'live' wire and two black 'neutral' wires twisted together in the same terminal. See below.

When disconnecting the two neutral wires from the light itself they pinged apart so then I couldn't tell which black wires were the original neutral pair and which was the single 'live'.

I paired up the two neutral wires that I thought went together, and connected it back up to the new light and it all works fine, but i'm concerned that I may have paired up one of the old neutral wires with the live, and put the other neutral wire in the live terminal of the light.

My question is, would I know if i've connected the wrong two black wires to the neutral terminal? ie, would the RCD pop or would the light simply not work? Is there any way to test the wires are connected correctly.

Your help's appreciated.

[sbowler]

If you had connected live to nuetral, I dont think it would work and also it would effect other lights on that circuit, wouldnt it?

[clockworks]

If you had connected it the wrong way, the light wouldn't work (using a neutral wire instead of the switched live), and the RCD would trip when you turned on the switch (switch would connect live to neutral).

If everything works, you've connected it the right way.

[digitalfm]

Thanks guys, sounds like I was lucky. Next time i'll mark the switched live with red tape.

Appreciated.

[niceguy235uk]

Originally Posted by clockworks

If you had connected it the wrong way, the light wouldn't work (using a neutral wire instead of the switched live), and the RCD would trip when you turned on the switch (switch would connect live to neutral).

If everything works, you've connected it the right way.

The RCD would not trip if the lighting circuits were not protected by it (which they shouldnt be).

However, if the lights were connected incorrectly with a neutral cable with live, you would introduce a short circuit and it would go ermm... bang.

[ZippyCat]

Providing everything is installed in accordance to BS7671, the MCB protecting the lighting circuit should trip under short circuit conditions.

[ZippyCat]

Originally Posted by digitalfm

Thanks guys, sounds like I was lucky. Next time i'll mark the switched live with red tape.

Appreciated.

Realistically the switched live should be marked with red tape or heat shrink anyway, as the installation has deviated from the recognised standard. In addition, the corresponding end of the cable located at the switch should also be marked.

[niceguy235uk]

Originally Posted by ZippyCat

Providing everything is installed in accordance to BS7671, the MCB protecting the lighting circuit should trip under short circuit conditions.

Yes, but not the RCD.

[Johnny Thunder]

This could be a TT system, which would require RCD protection. However, the
RCD should still not trip under short circuit conditions.

[ZippyCat]

Originally Posted by niceguy235uk

Yes, but not the RCD.

Hence why I didn’t say the RCD.

[clockworks]

To the general public, the terms RCD, MCB, ELCB, fuse, trip, circuit breaker, etc., are totally interchangeable.

While they are (mostly) different things, they all do basically the same thing - turn off a circuit when something goes wrong, even if the "something" is subtly different.