4mm2 for 32A

[sheng2]

Hi,

I have an incoming 32A single phase supply to a 16A equipment. To protect the equipment I installed a 16A MCB in between.
My question is for the cable from 32A MCB to 16A MCB, can I use 2+e x 2.5mm2 cable?

I know for 32A we are supposed to use 4mm2 cable, but the electrical shops nearby only sell cable in bulk, and I only have 2.5mm2 cable with me, so I wonder if 2.5mm2 is sufficient, since the 16A MCB will cut off when current exceed so, and in daily operation the current is less than 16A.
The 2.5mm2 cable will be less than 1 meter, freely hang along the wall indoor. Cable type is H07RN-F.

Thank you very much!

 

[Dustydazzler]

I would have no issue using 2.5 flex for this application

 

[Strima]

The 16 amp MCB will protect the short run of cable from the supply.

 

[Pete999]

Hi,

I have an incoming 32A single phase supply to a 16A equipment. To protect the equipment I installed a 16A MCB in between.
My question is for the cable from 32A MCB to 16A MCB, can I use 2+e x 2.5mm2 cable?

I know for 32A we are supposed to use 4mm2 cable, but the electrical shops nearby only sell cable in bulk, and I only have 2.5mm2 cable with me, so I wonder if 2.5mm2 is sufficient, since the 16A MCB will cut off when current exceed so, and in daily operation the current is less than 16A.
The 2.5mm2 cable will be less than 1 meter, freely hang along the wall indoor. Cable type is H07RN-F.

Thank you very much!

Carp

 

[Wilko]

Why not have the 32A mcb changed to 16A?
If we are talking wiring that forms part of the fixed electrical installation then no, a single 2.5mm cable will not be protected by a 32A mcb.

 

[pc1966]

It would seem strange not to look at simply changing the supply to 16A as easier than a 2nd MCB.

The answer as to whether or not your system is protected is not that simple. While the 16A MCB near the load should protect against overload, you should still verify that in the event of a fault on the cable(s) they are protected by the 32A MCB.

That means a check the the E conductor is large enough to meet the adiabatic limits for fault-clearing on a 32A MCB, and that the fault impedance at the end of the 32A section is low enough that it would still disconnect in under 0.4s

 

[Soi disant]

Why not have the 32A mcb changed to 16A?
If we are talking wiring that forms part of the fixed electrical installation then no, a single 2.5mm cable will not be protected by a 32A mcb.

Protected from overload?

That will be via this, that will:

I installed a 16A MCB in between.

Protected from fault current?

Do we really need to do adiabatic calculations for a 1m length of cable rated at 27A on a B32?

If this were a ring final with an unfused 2.5mm² spur supplying a DSO would you really object that the cable was not protected?

 

[Soi disant]

That means a check the the E conductor is large enough to meet the adiabatic limits for fault-clearing on a 32A MCB, and that the fault impedance at the end of the 32A section is low enough that it would still disconnect in under 0.4s

Loop tests at the new socket yes, but how many people carry out adiabatic checks when installing this:



?

 

[pc1966]

Do we really need to do adiabatic calculations for a 1m length of cable rated at 27A on a B32?

Reading it again, not really.

Initially I was thinking of T&E with the smaller E conductor but reading it again it seems to be 2.5mm H07RN-F which of course has a 2.5mm E. Also the short length means it should not have any disconnection issues.

Only real comment about that would be using ferrules as usually MCB terminals are not designed for fine-stranded cable.

 

[pc1966]

Loop tests at the new socket yes, but how many people carry out adiabatic checks when installing this:

Odd, your new post is saying "Yesterday at 11:09 PM"!

That is true, and a quick check in the OSG for Table B7 it has 1.5mm (i.e. T&E CPC size) as safe for all typical MCBs to 40A B/C curve provided the PFC is below 3kA which is probably the vast majority of cases.

 

[pc1966]

So short answer is fine for 2.5mm feeding 16A MCB, but remember the ferrules for fine stranded flex.

But just odd not to simply change the supply MCB (though if odd make, etc, might be harder to do)!