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Strange looking junction box for lighting

Postby Mbmagic » Thu Aug 05, 2021 10:09 pm


I have just pulled an old light fitting down from my upstairs toilet ceiling. It has a 4 socket junction box behind it that looks pretty old and had it so I’m replacing, the wiring just looks strange to me as a very basic level electrician. There is three cables feeding into it, each with a exposed copper earth, a red live and a black neutral. The three lives are all into one socket, the earths into one socket and then two blacks in one and one in the other. Then the cabling that was connected to the light fitting was just two wires one from the two blacks and one from the single black. Why would a light fitting be connected to three apparent neutrals and no live? Also was no earth connected. I have changed light fittings before but never with this much going in and never without apparently using any live. Was just going to put back as it was but just doesn’t look right.

Thanks in advance.
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Postby Mr White » Fri Aug 06, 2021 2:20 pm

Your basic level of understanding of electrical wiring contains errors.
The wiring you have is correct, the two blacks are neutral, BUT the single black is switched live. If you want to know more, google for "3 plate wiring system"

If there is a hand basin in the same room the light fitting will have to be totally enclosed (Usually a globe lamp) since most of these are double insulated no earth is required.

Ideally the switched live should have red sleeving, and the earths should have green sleeving.
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Postby ericmark » Sat Aug 07, 2021 12:13 am

As said that is the standard wiring, in theory there should be a red sleeve over the single black. In the UK the ceiling rose acts as a junction box, in many other countries they use the switch back box.

There are special rules for bathrooms, but not for sinks, so a standard ceiling rose and pendent is OK with a toilet, since 1966 you have to run an earth to ceiling roses, but the pendent can be class II and earth free. It should have a square within a square sign.

The ceiling rose is the odd one out, every other junction box you must require a key or tool to access live wires, but the ceiling rose can have a lid you can unscrew by hand.

However any junction box does need to follow the rules on tool or key, so having a 4 way block connector shoved into ceiling space is not permitted. Although quite common.

Some electricians doing EICR (electrical installation condition report) can be rather pedantic, so insulation tape can be removed without a tool so technically not permitted.

I have questioned when people say it needs a junction box, how does one remove floor boards without the use of a tool? But wooden junction boxes are no longer used, with domestic everything should be type tested.
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