DIY Doctor

lighting spurs

Postby phillip » Sun Aug 10, 2008 10:13 pm

Is it possible to take a spur from the back of an existing light switch on an upstairs ring circuit with a maximum existing demand of 500 watts (5, 100 watt bulbs) the current draw for the security light would be between 150 and 300 watts. The intention would be to switch from the same back box by replacing the existing single one way switch for a twin one way switch. The spur would be approximately 3 metres in length. Possible or dangerous?
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Postby kuzz » Sun Aug 10, 2008 10:31 pm

Sorry not a diy job. this type of work would be covered by part p. If you don't understand part p there are links that explain it on this site. I doubt you would have a neutral at the switch anyway, so you'll need another plan for wiring the light.
And just for the record i very much doubt your lights are wired on a ring. Probably be a radial. Some good diagrams on this site if you wish to try and understand it more fully.
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Postby ericmark » Sun Aug 10, 2008 11:18 pm

Normally no as there is normally no neutral at the switch.

Postby TheDoctor4 » Mon Aug 11, 2008 8:51 am

If you require information regarding Part P then we have a project covering this subject in our projects section under the title "Part p building regulations ".
You can view our projects section on the following URL:

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Postby ericmark » Mon Aug 11, 2008 10:04 am

Sorry Phillip Kuzz reply had be held up. In theory there are no jobs that can't be done DIY but in practice the local authority charges and restrictions mean that small outside, Bathroom and Kitchen jobs, become cheaper to get done by a registered electrician than DIY.
If the Light is mounted on the house wall it may not come under Part P but it is up to you to read and work out what is required it is so easy to miss things on a forum and give wrong advice.
but the main thing that I noted is you want to take spur from light switch which will have no neutral connection it would need to come from light fitting and with 150 to 300 watt draw you would need to consider the draw of rest of house normally 5/6 amp is maximum you can draw from a lighting circuit and thats approx 1250 watt.
Also it will need to be RCD protected and you have to consider where the RCD will be located.
In new houses all circuits are already RCD protected but in older houses the lights are seldom protected.
Many people will take supply from ring main and this is more likely to already be RCD protected.
As all these questions start to pile up and there is still a lot I have not mentioned like all the testing and inspecting paper work that will be required you can see why many consider this as not being suitable for DIY. I realize if I just say no you will try anyway so I have tried to explain why you should not DIY.

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