Electrical – Wiring a light fixture

electrical

I am replacing a light fixture in my bathroom with a LED fixture. My house is from the late 20s so there are some quirks. In this case I have 3 sets of wires into the box. There are 6 other lights, basically every light in the front of my house daisy chained from this fixture.

As far as I have been able to figure, one set of wires is from the breaker, one from the switch and one to downstream fixtures. Everything works fine until I add the new LED fixture. As soon as I add that and turn the power on the light comes on then when I toggle the switch the breaker trips. Is there an issue with the fixture being LED? The previous fixture worked, I just didn't like a chandelier in the bathroom.

Any help is appreciated as I am very frustrated right now. What should have been an easy task is now a PITA.

I am adding a picture so you can see what it looks like. With it wired like this and the switch off, all the downstream fixtures work but if I toggle the switch it blows the breaker.

enter image description here

Best Answer

Note: This answer was written before the photo was added to the question and country identified.

Problem

when I toggle the switch the breaker trips

You have connected the wires incorrectly. You have probably connected the switch between neutral and live.

Wiring a light fixture

In the UK, a pre-2004 ceiling box with three sets of wires would be connected like this:

enter image description here

A comes from the breaker, B goes to the next light fitting. The wires to the lamp holder use the post-1977 colours.

Note that C is labelled "twin red & earth" this means it has a second red wire instead of the black wire. In practise, most electricians use normal "twn * earth" for the cable to the switch. This means the black wire is switched-live not neutral. It should be marked with red-tape to indicate this.

If you then just connect all the black wires together, you would connect the switch across live and neutral, creating the problem you describe.

The correct wiring looks like this in a typical UK ceiling rose (with post-2006 fixed-wiring colours. Arrangement is inverted compared with above diagram):

enter image description here

Photo - own work, © RedGrittyBrick. Licence: Creative-Commons Attribution-ShareAlike 3.0

Note the red tape on the blue wire from the switch, indicating this is switched-live not a normal neutral. See that this particular wire is NOT connected to the other same-coloured wires (blue in this example).

Colours of wires

A brief history of wiring colours in the UK

                     neutral     live     earth
Before 1977:         black       red      green
1977-2004:
   Wires in wall     black       red      green
   Other† wires      blue        brown    green/yellow striped
After 2006‡:         blue        brown    green/yellow striped

† pendant light cords, appliance cords, lamp cords, etc  
‡ Between 2004-2006 you could use either set of colours in fixed wiring in walls.

Other countries

The same principles apply but the wiring colours will differ. For example, the US usually has white for neutral, black for hot (live). The specific methods for connecting wires will differ. For example, a US home will probably use wire-nuts.

However, to repeat, the principles are the same, make sure the cable from the switch is not connected incorrectly, you do not connect all wires of the same colour together.

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