DIY Doctor

Fuse Keeps Blowing After Adding Light and Switch

Postby brainiiii » Tue Aug 20, 2019 5:51 pm

so, had a perfectly working external sensor flood light connected to power originating from a fused heater switch (which borrowed power from a near by plug inside the house). all good.

today though, i cut into the wire, connected a new light switch and a new light. the goal was for the new switch to control the new light, while the sensor light to remain the same as before.

now, with the switch at one position, the sensor light works as before, and the new light stays on. when i flip the switch though, the heater switch fuse blows, and both lights no longer work of course.

i have checked and there are no visible wires touching other wires but perhaps i joined them wrong? all neutrals together, same for live and ground.

thanks
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Postby Mr White » Wed Aug 21, 2019 5:21 pm

You have wired the new switch across the supply, which is why the fuse blows when you operate the switch.

You have also wired it in a dangerous condition, as well as using the wrong cable.

I would strongly recommend that you get someone in to do the job properly for you. (It does not have to be an electrician)

I read somewhere a note which I feel is very appropriate in this instance.

"Electricity has no prejudices, it will kill anyone"
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Postby brainiiii » Thu Aug 22, 2019 7:49 am

hi, thanks for the reply, I know I messed up. Upon reading online and thinking more clearly, I have connected the switch the correct way (terminated the N cables on a connector, and correctly connected the Live cables to the switch) and now it works with no fuse blown / anything tripping etc. I have also covered the cables with electricians tape and tucked them behind wall tracking.

By dangerous condition I assume u meant the naked cables being exposed?
By wrong cable what do u mean? It's the cable I had in hand, normal british standard L,N,G cable 220v. Did you mean it would be ideal to use the cable with only N and L?
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Postby ericmark » Mon Aug 26, 2019 2:17 pm

We have a set of rules designed to keep things safe. Some have nothing really to do with the electric part, but tell you switch heights and safe routes, and if everyone uses safe routes, then we know where we can put a screw without hitting cables.

There is nothing wrong with using flex, but things like maintenance free junction boxes don't work well with flex, but some basic rules are you should not be able to access a live part without the use of a key or tool, with the exception of the ceiling rose and pendent lamp holder which tradition has allowed one to access by hand, although there are now shuttered versions of the BA22d lamp holder where you can't poke your finger in and get a shock.

One of the big problems is although some thing fitted in 1950 complying with the rules at the time can be left as it is, once you add to it, then it must comply with todays regulations, so before I can fit a new socket, I have to insure the supply is RCD protected, but the old one can remain without it.

Also running cables one now have to consider what happens in a fire, use of plastic clips is OK as long as if all those clips melt, the wires will not fall on any firemen. So inside trunking we now have to fit metal clips every so often so cables can't fall, where 10 years ago we could fit plastic sticky back trunking and use some decorators chalk which once dry would stop it falling off again.

As to which bits Mr White was looking at I don't know. And since it was work in progress it may be OK now, but insulation tape can be removed without a tool, so we have to use little plastic boxes with a small screw to hold lid shut so a tool is required to access live parts.
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