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Topic Title: CSA for 70w Halogen light circuit
Topic Summary: What CSA?
Created On: 19 January 2014 11:26 AM
Status: Post and Reply
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 19 January 2014 11:26 AM
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ennaress

Posts: 3
Joined: 19 January 2014

Hi
I am new to the IET, now studying Part P Defined Scope (First month!) - but years of 'DIY'...
My project is a basic circuit consisting of 2 No. 35W Halogen downlighters for Mrs and Me bedside reading.
Wish to spur via FCU and Joint box and 2 No. single switches.
I realise this may be totally OTT, but I want to do it to apply some of the basic techniques I'm studying. Plus, any opportunity to get the tools out...

My Question: what CSA conducter should I be using between:

- the socket outlet and the FCU; and
- the FCU and the remainder of the circuit.

Or should it be the same size throughout?

I'm reckoning on a 1A protection and 1mm conductor - but can you use 1mm conductor as a spur?

Cheers
 19 January 2014 12:04 PM
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daveparry1

Posts: 6169
Joined: 04 July 2007

No, 1.5mm from socket to spur outlet provided it's whithin 3m of the socket and not likely to suffer mechanical damage, (mentioned in BS7671 somewhere!) otherwise 2.5mm.
1mm is ok from spur outlet to lamps. 3 amp fuse in spur outlet,


Dave.
 19 January 2014 12:10 PM
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hertzal123

Posts: 300
Joined: 26 August 2007

Without allowing for any derating for thermal insulation etc,it would normally be 2.5 from ring final to spur and then 1/1.5 to lights.
Regards,Hz.
 19 January 2014 12:16 PM
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hertzal123

Posts: 300
Joined: 26 August 2007

Originally posted by: daveparry1

No, 1.5mm from socket to spur outlet provided it's whithin 3m of the socket and not likely to suffer mechanical damage, (mentioned in BS7671 somewhere!) otherwise 2.5mm.

1mm is ok from spur outlet to lamps. 3 amp fuse in spur outlet,

Dave,
Thought it had to be 2.5 from socket to give short
circuit protection from a 32A mcb?
Hz


Dave.
 19 January 2014 12:36 PM
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daveparry1

Posts: 6169
Joined: 04 July 2007

The 1.5mm will give s/c protection and there's no chance of overload due to fixed load / fcu. It is stated in 7671 (but not easy to find!)

Dave.
 19 January 2014 12:44 PM
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daveparry1

Posts: 6169
Joined: 04 July 2007

I will however add that I usually use 2.5mm from socket to spur unless the spur is right next to the socket. As the OP is doing a project I thought they might mark him down for using 2.5 mm unnecessarily?
 20 January 2014 10:27 PM
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AJJewsbury

Posts: 11374
Joined: 13 August 2003

The 1.5mm will give s/c protection

er, including the 1.0mm c.p.c. usually found in 1.5mm2 T&E ?
- Andy.
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