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this is the reason im awaiting to start design course so i dont have to ask for help anyway we are to run a 4 core 70mmm swa cable 30 metres to a section board from the section board we are to run 2 x 4core 35mm swa to supply 2 three phase tp&n 6 way 125amp db the length of these cables is only 10 metres so the 4 core 70mm clipped direct can take 238amps ok and 4 core 35mm can take 154amps so both boards are to supply commando sockets all 16amp but no one is really telling us the max demand can i use 125amp the rateing of the board and times it by 0.4 to give me max demand if not help
 
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  • #2
a bit more info dragged out of client for max demand value in the db they require 2 x 32a 6 x 16a and 2 x 20amp breakers can i add all these breakers together and multiply by 0.4 to get my max demand would this be ok
 

telectrix

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i'd assume lighting on all the time, no diversity. then try and ascertain how many outlets will be in use at any one time. chances are anything from 20% to 80%.
 
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Tel high bay lighting fed from another board this is for 2 small photo studios can I not add breakers up and multiply by 0.4 would that not give me max demand or are you saying add all breakers up and work out 80%. Of the value
 

topquark

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Arms
The reason you've not had many responses is there is not enough information (so far) for anyone to make an informed decision and hence offer advice. We'd need to better understand the loading and usage of each of the circuits.

You also appear to have decided on cable sizes already so what was that decision based on?
 

Des 56

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The only way you can estimate the maximum demand is either with a design drawing or information off the client regards its likely use
The type of load for the equipment that they will be using,the frequency of use. the cumalative figures for those loads

Legions of 16 amp sockets can be used for extra light loads, or lots of heavier gear and the figures can be miles apart
.I think you should gleen the information from the client
 
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Based on the fact that a 4core 70mm swa is oo to supply a section board that supply's 2 125 amp DBS fed with 4 core 35 mm swa the reason we decided on this is that's how it's done in the studio were there moving from when we asked photographers what they required they gave us 2x 32amp commando sockets 6 x 16amp commando sockets and 2 x 20 amp supply's for metal clad sockets what other info can we possibly ask for just wondering and hoping are cable sizing will be ok
 
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  • #9
Des totally agree with you but it's a retail group and there's no one there really with ant electrical back ground it's always been pushed on to are toes that's why I'm going to de sign course so I can do it properly myself in future but they have told us the demand hence the breaker sizes for individual commando sockets
 

topquark

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Arms
Ask them what's being plugged in to the sockets, and the equipment's usage characteristics. Otherwise we'd be just guessing.

You'll need that info anyway when it comes to considering OCPD's for the circuits. I doubt you'll need much other than type B's for a photo studio, but who knows what equipment they'll want to use.
 
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  • #11
Thanks for your help top won't hold be breath with them honest they make it up as they go along for a big orginization there clueless but thanks any way we've never had any proper drawings in the four years we've been there and we've done a fur few refurbishments
 

plugsandsparks

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I would write to them and state your max design current for the installation. this looks like 125A for each board and whatever is protecting the 70mmsq cable as a overall total. Tell them thats the max the solution will give.

Otherwise its a meaningless , pointless exercise if you dont know the type and usage of equipment. As already mentioned some loads are "full load" "all time" e.g. lighting, heating is another high end usage, computers are on all day.
Anything like a machine, say with a motor or solenoids rarely run at full load for any length of time so these can be factored down, also some equipment is used occasionally so can almost be left out.
end of the day its a guess, hence state to client you maximum supply criteria.
 
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