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Topic Title: Mixing cable sizes
Topic Summary: Can it be done
Created On: 06 March 2019 08:44 PM
Status: Read Only
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 06 March 2019 08:44 PM
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Ketla17

Posts: 4
Joined: 08 September 2018

I have been wiring some down lights and have run out of 1.5mm would it be a problem to finish wiring with 1mm to loop the fittings together
 06 March 2019 11:29 PM
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Dave69

Posts: 789
Joined: 16 July 2011

No problem at all as long as the MCB protecting the cable is the right size. Getting two 1mm cables into downlights is also much easier than two 1.5 cables
 07 March 2019 07:08 AM
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Ketla17

Posts: 4
Joined: 08 September 2018

So it's ok even if I have wired half of the circuit in 1.5 and then do the rest in 1mm.
 07 March 2019 08:09 AM
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dustydazzler

Posts: 3068
Joined: 19 January 2016

I always do this with 2way switches, as in use 1mm 3C and earth cable

Another plus for using 1mm is As Dave says it is much neater and easier to dress 1mm cores into downlight junctions

Also 1mm is cheaper
 07 March 2019 10:35 AM
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broadgage

Posts: 3170
Joined: 07 August 2007

Yes, mixed cable sizes are fine provided that the smallest cable is compliant for the size and type of OCPD.
AND that the voltage drop for the entire circuit is within acceptable limits.

Care must also be taken to ensure that any specifications by architects or consultants are still met of course. If the spec says "a minimum of 1.5mm on lighting circuits" Then you must do exactly that even if 1.0mm would otherwise be fine.

Also be aware that 1.5mm is now the minimum for power circuits, and that pedantic inspectors might consider that a circuit used primarily for lighting is in fact now a power circuit if an extractor fan or TV aerial amplifier is connected thereto.
 07 March 2019 05:14 PM
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AJJewsbury

Posts: 17795
Joined: 13 August 2003

and that pedantic inspectors might consider that a circuit used primarily for lighting is in fact now a power circuit if an extractor fan or TV aerial amplifier is connected thereto.

Then point them to NOTE 4 on table 52.3 in the 18th
- Andy.
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