Discuss 4 or 6mm2 cable? in the Commercial Electrical Advice area at ElectriciansForums.net

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Now then. Need some help determining what size cable to use. Circuit consists of 7x HS2000/600watt lights, 230v.50hz taking 3.3 Amp each. The fittings are going to be hung in a straight line using chain hooked round Unistrut. We are wiring in lsf singles in plastic tube stemming from 4x4 metal trunking. It is a radial circuit and we are putting 7 MK Masterseal sockets in a line, one above each light and then using a curly flex with a 13 Amp plug top on each, From the board to the furthest MK socket will be 10 meters - the nearest socket is about 4 meters. The person who is putting his name to the design is demanding that we use 6 mm2 cable protected by a 32 amp breaker (c Type) but I think we could well use 4mm2 cable coming from a 25Amp breaker (c Type). There is the grouping factor to be taken into account but not the insulation factor. He initially he wanted to use 10 mm2. Am I missing something? Thanks in advance for any answers or theories.
 
so. this guy is putting his name on the design. he wants 6mm, then give him 6mm. any comebacks, it's down to him. if it's wrong, it's his problem, not yours.
 
4mm sounds about right without knowing what sort of grouping factor needs applying. Breaker size will depend on calculated cable size to be installed. I wouldn't of chosen a D type breaker... Why are you changing from metal trunking to PVC conduit?? Why not metallic 20mm conduit?? Or is that a silly question?

I'm just trying to work out why you need 7 X 600W fittings in a space of around 6 meters. Going by your statement of socket outlet distances from DB, being nearest 4m and furthest 10m??
 
I'd use 16mm just to be sure. :)

Seriously, if you're not speccing the job, just get on with it. In the instance you're describing, it may well be over-engineered, but doesn't look like it will be dangerous!
 
Would you even be able to squeeze two 6mm singles in to each terminal??!! Never mind 10mm LOL!

Well there is one guy here that reckons he can get 3 X 4 mm cables into a socket outlets terminals with no problem, which amounts to the same total CSA, (12mm)!! lol!! Personally, i wouldn't even try!!
 
4mm sounds about right without knowing what sort of grouping factor needs applying. Breaker size will depend on calculated cable size to be installed. I wouldn't of chosen a D type breaker... Why are you changing from metal trunking to PVC conduit?? Why not metallic 20mm conduit?? Or is that a silly question?

I'm just trying to work out why you need 7 X 600W fittings in a space of around 6 meters. Going by your statement of socket outlet distances from DB, being nearest 4m and furthest 10m??

Thanks mate The changing to the plastic tube is part of the costing. We are actually wiring grow rooms up at Bristol University for want of a better description "Large Cannabis Farm" and all legal. According to the online cable calculators (without any grouping factors) I can use 2.5mm, this is why I'm querying his decision to use 6mm when there is no need. But as someone else posted-- The book stops with him.
 
I'd use 16mm just to be sure. :)

Seriously, if you're not speccing the job, just get on with it. In the instance you're describing, it may well be over-engineered, but doesn't look like it will be dangerous!

Yes mate we will do but you know when you get that bit between your teeth when you know your right the so called designers wont budge -- just to be right. ****es you off abit
 
could the high ambient temperature be a factor in his calculations?
 
could the high ambient temperature be a factor in his calculations?

mmm I asked that question t my boss last week when this saga started. He sort of backed me up by saying that when functioning the BMS system doesn't allow the temperature to exceed 30 degrees--coz it with fry the plants. But , on the other hand we had to come out of the Gro-dome (posh greenhouse) today at 2pm because the temperature was off the scale (50 degrees plus)
 

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