"Jamie" t wrote in message
...
Andytaylor1963 wrote:

Can any one help please? I am attempting to install a new ceiling light
in a single switched single light configuration in our downstairs
toilet. I dismantled the old light and re-wired the new light in excatly
the same configuration as the old one. There are 2 black wires, one red
wire and one earth wire. I have established that the red is the switched
live by testing with a circuit tester. When the light is switched on the
neutral terminal becomes live when a bulb is inserted so the circuit is
completing itself but the bulb stubbornly refuses to light up. I have
exchanged the light unit thinking it may be faulty bu to no avail. The
red is insterted in the "L" part of the block and the blacks are
inserted in the "N" part of the block. The house earth is attached to
the light fitting earth correctly so I am now at a loss. Help
please...... Thanks




You have something wrong there.

L should be the black wire, White wire goes to N.

As for the Red wire? That sounds like you have a three way switch?

three way switches normally use 3 wire with ground. That would be the
Black, white and red + ground wire.

In all cases, the white wire is (N) the neutral.

The black/Red is considered L in your case.

If you don't have a white wire, you better check a little closer.

I suppose you could be using 2 leads of romix, It isn't unheard of
but does cost more. In which case, you then wouldn't have a red wire but
2 black wires and still a white wire.


Jamie


That's U.S. wiring Jamie. This guy is talking UK wiring. What he has is
(almost) absolutely bog-standard wiring for a ceiling light in the UK. I say
"almost" because there is normally at least two, and often three or four
reds going to the ceiling rose, and two blacks. The blacks are neutral in
and loop out to the next fitting on the circuit. Two reds are live in and
loop out to the next fitting. You can normally identify those because one
red and one black each come from a twin + earth cable. The other two reds
are the switch drop - one out and one return. These usually are together in
another twin + earth cable that's made specifically for switch drops. All
the colours changed recently, but up to a few years ago, all house wiring
here was in red, black and open copper earth, sheathed with a yellow and
green striped sleeve where it terminated in a fitting.

The usual arrangement in the ceiling rose, is two blocks of three terminals,
and a two, although this can vary. Typically, the two neutrals are in one
three way, along with the neutral from the pendant cable, the two lives are
in the second three way block, along with one of the switch drop wires, and
the other switch drop wire is in the remaining two way block, along with the
live from the pendant cable, so the ceiling rose performs the dual function
of light fitting, and junction box for the continuation of that lighting
circuit.

The fact that the OP has two blacks and only one red, is confusing. That
basically implies that the live feed for the switch, has been 'stolen' from
some other circuit, with only the switched return finding its way back to
the ceiling rose. This is further confused by the fact that there are two
blacks, implying that the same has been done at the next fitting on the
circuit as well. It would be a good idea to check exactly which circuits
these lights are on, in case some cowboy electrician or builder, has stolen
these lives from a ring main circuit at some time in the past. I have seen
this done on more than one occasion, where it was inconvenient to run new
cables into ceilings.

The fact that the neutral becomes live when a bulb is inserted and the
switch is on, in no way implies that the circuit is "completing itself".
This tells us that the neutral is 'floating'. Assuming that this is a
pendant fitting, are you measuring this behaviour at the blue neutral
pendant wire ? If so, I would suggest that you look carefully at the
configuration of the terminal blocks in the fitting. They can vary, and may
not be the same as in the fitting you are replacing, in which case, I think
you will find that your blue wire is not being joined to the two blacks. So
just to get it straight, your two blacks and the blue neutral pendant drop
should all be commoned together in one block, and the single red and the
brown live pendant drop, should be commoned together in a different block.

Arfa