Swa 4core cable used as two 2core circuits

[mickfred]

Working on a job have found a 4core cable going into a weather proof box and splitting up into 2 circuits again at the board it split in two single phase MCB s . My question is would you judge the current carring capacity of the cable as a two wire or four wire

 

[mickfred]

Well it is related to something else that happen lately all my large swa off cuts have been robbed and a 35 meter lengtt of 50mm 4core which I cut out off the ceiling cos it had been damaged has went as well . That was my graft and some pr#£k has robbed it before I could

 

[westward10]

I did a job feeding two portacabins about six months ago and used two 3 core cable two feed them and it got me thinking when I seen this today as the two feeds had to be run though ducting and both had to be put in weather proof box es to be connected to flex to be plugged in to the portacabins and I thought it would of been cheaper and quicker to do this if I had a similar job in the future

No reason why you cannot do this providing the armour is effective for earthing purposes, the drawback is if it is required to support main protective bonding where the minimum size to support 10mm bonding would be a 50mm 4 core cable.

 

[mickfred]

Sorry about the multiple reply phone just messed up

 

[mickfred]

Well in truth the cable is 5core but I was using 4core as a example

 

[Wilko]

I always consider the three phase ccc, same for a three core cable as a single phase supply with one core used for a cpc. I think the Tables in 7671 should be reconsidered as they only consider two core for single phase and three or four core to be three phase. Ccc for YY, CY and SY apply correction factors for core quantity as opposed to the number of phases and I think think this is more informative.

I know it's not "right", but I'm thinking 2.3.3.1 which would give a Cg of 0.5 here (?).

 

[Darkwood]

What would you think about for isolation of the cable ... I'll throw that in the ball park

 

[Spoon]

I'll also throw in 'grouping factors'

 

[westward10]

A multi-core cable containing more than one circuit is no different to containment systems carrying multiple circuits.

 

[johnduffell]

Isolation is no problemp you isolate the circuits and test for dead until the are no more volts. Same as isolating a 2 gang light switch on two circuits

 

[johnduffell]

A multi-core cable containing more than one circuit is no different to containment systems carrying multiple circuits.

Agree i think the difficulty is looking up all the data installation methods etc

 

[Darkwood]

I would suggest if the cable got damaged and a fault occurred on one circuit only that it should shut down the whole cable, I would personally use a 4 pole breaker and clear labelling, then split at load end.

The regs really don't cover methods like this but if approached logically then not a problem in my honest opinion.

 

[westward10]

This isn't necessary and would not happen if the cable contained a single three phase circuit with protection by way of individual fuses.