I'm renewing the wiring in a workshop. Mostly single phase but also a couple of small 3ph saws and an old 3ph 480A arc welder (lovely machine). How would one calculate what size breakers to use for the welder? In normal use the welding machine works at 150-250A. I have googled but the results are confusing to say the least. Thanks, Nick.
Surely the nameplate will give an "input" current rating? Also note the type of circuit breaker for welders is typically a type D and required earth fault loop impedances are significantly lower than for type B. Maybe you need to get some training in electrical installation design, BS7671 and the on-site guide?
OK here are some crude calculations, From memory a DIY welder will give out about 180A on a 13A 230V socket. Times that by 2.7 gives 486A out 35.1A in. Divide over 3 phases gives approx 11.7A per phase. A 16A 3ph MCB should give adequate protection and enough overhead for "surges". I would use 4mm cable, although in theory 2.5mm would be ok for shortish runs. If You are not sure about ANYTHING please consult elsewhere. If the welder was in use, what was it fused at before? Allan
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