current carrying capacity

[gary_b_efc]

Hi, quick question. 4 core 4mm armoured will carry around 30 amps. What will it carry if the cores are doubled up? I'm not planning on doing this by the way, it's installed already in a house I'm testing. Thanks.

 

[Doc Hudson]

Try thinking if you had two separate 4.0mm circuits each carrying your 30Amps, how much is the combined capacity? Or consider a ring main 2x2.5mm cables what does the capacity become? there is a chapter in the BS7671 about parallel circuits.

Doc H.

 

[gary_b_efc]

ok, maybe I asked the question a little too quickly. The armoured cable in question is supplying a sub board in an extension of a house. The board feeds the kitchen ring, cooker, shower and lighting circuits. It currently has no overload protection, just connected with henleys to the incoming, and is just using the armour for the cpc.

I'm going to run an extra earth to boost the size of the cpc and move the supply from the henley blocks to a small 2 way shower type board to give protection. I need to work out what breaker to fit in, 40,45 or 50.

 

[PC Electrics]

From 4D4A, 4mm pvc armoured is 38A RM1 (you should assume it's pvc unless you can be certain it's xple). Others who do this sort of thing in Industrial stuff will be more precise than myself , but I seem to remember that if you double up the cores in a multicore cable then the ccc multiplies by about 1.6. This would give you a ccc of 60A.

Wait for others opinions before rushing off taking my word for it though.

I think I'd be leaning toward replacing it with a 10mm t&e (64A RM1) unless there's other reason for it to be armoured - if you can run a new earth surely you can run a new cable.

 

[gary_b_efc]

Thanks. All down to cost, as usual, so I wont be able to replace the cable. Fully finished decorated house in serious need of a rewire that wont get done. Just trying to make the worst bits a bit better.

 

[PC Electrics]

Ah, yes. We've all been there. Stick it on a 50A then. If they have trouble with tripping they'll just have to lump it or change to a gas hob.

 

[Evans Electric]

Call it 50A , that should be plenty for what you need, so 50A MCB , SWA is the earth . Is it glanded off properly.?

 

[gary_b_efc]

Not at the moment, but it will be when I go back. There were a few more serious matters that needed putting right first. I will be fitting new 10mm bonding as that also seems to have been overlooked, so I will run an extra 10mm to the sub board to give a good CPC. Complete mess of an installation, like I said earlier, just trying to make the best of a bad job.