DIY Doctor

Extending Lighting Circuit

Postby watersheddings123 » Sun Jun 29, 2008 10:05 am

Hello all.....

I am planning the lighting circuit for an extension to my house and could do with some help on calculating the circuit load and cable sizes.

I currently have 10 lights on a separate upstairs lighting circuit. This is protected by a 6A breaker.

The missus has a grand design plan of adding another 13 50 watt spotlights in the extension but I have concerns on whether a new 10A breaker will be required and what size cable will be needed.

How can i calculate the size of the breaker required and what safety factors are required to be added into the calculation?

I am also concerned that the size of the cable i was intending to use (1.0mm2) may need to be uprated? How do i calculate what size cable is required?

Sorry for the long topic.
Many thanks for your help.

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Simply Build It

Postby ericmark » Sun Jun 29, 2008 12:22 pm

In true Blue Peter style one I did earlier see if this helps?
Today testing of electrical installations is taken seriously. So what are we testing for?
We must insure should there be a fault the system will switch of within a set time. There are two main faults.
1) Too much current flowing.
2) Current flowing to wrong place.
To start with too much current flowing not only must it break the circuit it must do it in a safe manor and there is a limit to how much current the devices can handle also there may be a difference between overload and short circuit. So a device may have a overload value i.e. 16 amp and a short circuit value B and a maximum handling current 6kA and there will be tests to ensure all this is able to happen.
a) to carry 16 amp the wire will need selecting as to how hot it will get which will change according to how much heat it can get rid of so clipped to a metal tray 1mm² will do but in a stud wall with thermal insulation 4mm² will be required.
b) To trip in the case of short circuit a “Bâ€

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