Help! Wierd electrical wiring uncovered

Hi,
Wondering if anyone could help at all with this. We are replacing some flush ceiling lights in our home as the current ones haven't been changed probably since the house was built in the 70's.

When taking off the exsisting light, we have discovered that is was wired up in a very strange way and we're not sure what to do with the replacement light.

The old light was connected up in the following way:

Two mains cables from the ceiling, each with an earth (bare), live (red)and neutral (black).

The two earths are wound together, twisting round each other but were not connected to the light.

The two red live wires were together, bound together with insulating tape but again, NOT connected to the light.

The old light was connected to the two black wires, one in each of the L and N connecting sockets, although there is no indication on the light which is which.

We can't even work out how the old light worked but it did!

We're now faced with this dilemma- what's the best thing to do with the new light?

Can we:

a) Try and isolate one of the mains cables and wire the light up correctly, using the L, N and Earth from only one of the mains cables? (Is it safe to tape the other cable up inside the light?)

b) Try and wire the new light up in the same way as the old, although we have no way of knowing Which of the two black wires went into the L and N sockets in the old light.

C) No idea!!

Any help/ideas why it's been set up like that would be much appreciated.

We can't really afford an expensive bill from an electrician so if we can possibly sort out ourselves, that would be ideal.

Thanks in advance!!

This sounds as if it is wired the same way as 99% of properties. You are assuming it is incorrect when it is not.

One of the blacks should have some red sleeve to identidy it as a switched live.

The earth should have sleeving on them and connect to the earth terminal of the light.

I would say the lights you have are not original and where put up by a diyer after the intial install.

//www.diynot.com/forums/viewtopic.php?t=37582

Thanks for the reply- that's good to know. We did look on the wires and there's no red casing anywhere unfortunately.

We also have had one of the light switches that tripped during this process- it's now stuck in the 'on' position and won't let you move the switch at all- a safety feature. Can this be reset?

Thanks!

Sounds like you ballsed up the wiring by confusing your black for a neutral when it is a switched live. This has caused your switch to fail (the fault current has arced and welded the switch closed). It will need replacing.

This should get you thinking....

That makes sense- well we had a 50/50 chance as there was no way of telling the two apart. Thanks for all the info- really appreciate it

There was a way, and it was the way that you should have followed:

Acquire knowledge of how lighting circuits work, and a multimeter.

Actually - there was another way:

Acquire knowledge of how lighting circuits work and from looking at how the old light was connected up realise that it's obvious what goes where and why.

What made you think it was OK to just dive in, using guesswork and knowing that you didn't understand how it worked?

But but but - you only have 2 cables, one black is neutral and one is switched live, and it doesn't matter which goes to the L and which to the N on the light, so what did you do?

Although the light will work with each of these two blacks either way round you should find out which is which.

It could prove to be misleading in the future during maintenance if something believed to be neutral is live, etc...

The black that is switched live should be the black at the switch.
WITH THE POWER OFF you could do a simple continuity test with a test meter to confirm which is the switch live.

Ideally you should sleeve this black wire with red sleeve, it goes to the L of the new light fitting.