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Discuss Rating factor within an enclosure? in the Electrical Forum area at ElectriciansForums.net

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lurch

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I seem to recall there is a rating factor that can be used within an enclosure effectively uprating the current capacity of the cable. Does any one know what this is and can it be found in BS7671 or is this a rule of thumb (?) for switchboard manufacturers?
 
Is this an existing enclosure mate or are you designing it?
A bit more info please.
 
I recall if you are running cables lets say in trunking, (metal containment) there is a factor to apply , that will uprate the ccc. But I cannot give you figures it's a long time ago.
 
It doesn't up rate the CCC of the cable at all.

I think you're referring to a fault free zone, which is limited to 3meters.

If I understand what your asking, an example. 25mm cable connected to a bus bar system backed with 800A fuses. So long as that 25mm is terminated into a suitable ocpd within 3 meters and is mechanically protected along it's route. It's all good.
 
It doesn't up rate the CCC of the cable at all.

I think you're referring to a fault free zone, which is limited to 3meters.

If I understand what your asking, an example. 25mm cable connected to a bus bar system backed with 800A fuses. So long as that 25mm is terminated into a suitable ocpd within 3 meters and is mechanically protected along it's route. It's all good.
yep I'm fine with that one, but thanks for feed back. (BTW ...ocpd = obsessive compulsive personality disorder? ;-) )

For instance when I look at a domestic cu with a 100a mainswitch fed from a DNO cut out with BS88 100a fuse we would put 25mm tails in. I look at the neutral lead and sometimes the live lead within the board supplied by manufacturers these are no where near 25mm and I doubt if there rated at 100a but clearly somewhere there is some rating factor that switchboard manufacturers use that allows this. . . .

Also may moons ago I had a electrical clerk of works condemn a switchboard in a commercial scenario that and been supplied with same. . . we engaged the manufacturers and met with said CoW and they pointed him in the direction of this "uprating" factor, for want of a better word, and it was accepted.

hope this helps/clarifies where I'm coming from
 
Yes, I see where you're coming from.

As far as I am aware there is no rules for "up rating"

However, BS7671 CCC ratings have a huge safety margin written into them. Ever seen how much current is needed to raise 2.5mm to above 70deg in open air.

If a manufacturer can prove through type testing that a smaller CCC is safe for use, that will overrule 7671
 
Rob. Agreed with regards to the safety margins, and in a lot of cases well over the top.

Off at a tangent a little. . . but still on current carrying capacity. If one doubles up on two cables would this simply double the current carrying capacity ?
 
Rob. Agreed with regards to the safety margins, and in a lot of cases well over the top.

Off at a tangent a little. . . but still on current carrying capacity. If one doubles up on two cables would this simply double the current carrying capacity ?

If you're using normal cable calculations then yes effectively.

Delve a little deeper into it and then no, there will be a difference. Nothing to worry about at the level we work at.

However 2 x 70mm wires will take more than 1 x 140mm wire.
 
If you're using normal cable calculations then yes effectively.

Delve a little deeper into it and then no, there will be a difference. Nothing to worry about at the level we work at.

However 2 x 70mm wires will take more than 1 x 140mm wire.
that was my understanding also. But lets keepit simple !!!!!!!
 

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