another cable calc

[revjames]

Heres another one for ya

2 fridges in a commercial kitchen. Each is 1200W. The plan is to have a single circuit feeding 2 FCU outlets.

This is what I got. Its conduit / trunking and there are 3 other circuits in the same run. so Cg is 0.65

so Ib = 2400/230 = 10.5a

In 16a

Iz = 16/0.65 = 24.6a too much for 2.5 singles method B

So a 10.5a load has to be fed in 4mm because there are other circuits in the same conduit/trunking run?

In the real world I doubt anyone would put it in 4mm!

 

[danny7299]

Supply voltage = 230 Volts

Ib - design current = 10.4 Amps

Protective device type = MCB type C

In - protective device rating = 16 Amps

Length of run of cable = 10 metres

Power factor = 1

Cable Type : General purpose PVC - Singlecore

Installation Method : Non-sheathed cables in Conduit on a wooden or masonary wall, or spaced < 0.3 x cable diameter from it.

method B

Ambient temp = 35

 

[revjames]

OK thanks Danny - did you do all that from the books or have you got Amtech or something? appreciate the detailed reply. Given its an assignment not a real situation, the assumption we have been given for the whole project is 30C so its only Cg we are concerned with. In the real world a short run like that no question most would throw a bit of 2.5mm in!

 

[revjames]

OK cracking on with the assignment and decided on sticking extra DBs in a couple of areas to help spread the load, get less grouping and generally get more sensible cable sizes. The DBs will be fed in SWA from the main CCU. Is there a size of SWA at which the earth continuity becomes insufficient or do you always run a separate earth of the same size as live conductor? TBH not seen anyone use SWA as sole means of earthing for a while.

 

[Zeespark]

As far as I am aware James, you can go upto a CSA of an SWA cable of 90mm2 whilst using the armouring to earth the cable. 120mm2 + needs a seperate earth cable.

AndyGuinness

 

[revjames]

Thanks Zee, thats what I thought, however as its just an academic exercise I might just run earth cable with it. dont think I can lose points for being over cautious. I think as long as it conforms to BS7671 I am OK.

 

[Zeespark]

I was incorrect. it is 90mm2 but there is no actual 90mm2 cable only 95, so I would put one in at that size and use armour on anything smaller than a 70mm2. Sorry to have screwed up royally headbang

AndyGuinness