# Cable sizing

Discuss Cable sizing in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

#### thomaspotato

##### -
Hi all,

I am trying to calculate a SWA 4 core that will be protected by a 250 amp switched fuse isolator. It is going to supply a 3 phase electric boiler that pulls 209 amps each phase at most. I'm filling in the parameters to an online cable calculator ,when asked for the voltage i've put 400 v, when asked for load in amps i've put 250 amps. Is this correct or should i be putting the total amps 627 because thats the total 3 phase load?

I wouldn't trust any online tool with this calculation. No come back if specified cable is incorrect and that could be costly. Better to calculate yourself and know that all factors have been accounted for and result is correct. Load will be per phase as they taught you in college.

I wouldn't trust any online tool with this calculation. No come back if specified cable is incorrect and that could be costly. Better to calculate yourself and know that all factors have been accounted for and result is correct. Load will be per phase as they taught you in college.
Yes you are probably right but can someone recommend a software i can use? 30 year since i was at college and i can remember the time it took to size a cable with all the factors

There is plenty of software out there but at a cost!

If you haven't needed it for past 30 years, it wont be viable to buy a package for this one off project.

DPG
Hi all,

I am trying to calculate a SWA 4 core that will be protected by a 250 amp switched fuse isolator. It is going to supply a 3 phase electric boiler that pulls 209 amps each phase at most. I'm filling in the parameters to an online cable calculator ,when asked for the voltage i've put 400 v, when asked for load in amps i've put 250 amps. Is this correct or should i be putting the total amps 627 because thats the total 3 phase load?

The total current capacity of the system in amperes is the same as the per-phase rating when referring to a balanced three-phase system. Thus, a 200 amp 3 phase service provides a total of 200 amps across the three phases, not 600 amps..

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