I am having trouble figuring out how to size the following scenario.
I have a customer that has an existing installation of 4 welders. They are automated machines and they were built by the customer so there is no load information to go by. All are 480V 3 phase. Two are currently being fed with 400A breakers and two are being fed with 150A breakers. They way the process operates they weld for about 1 to 2 seconds then they are not welding for mabey 15 to 20 seconds while the 2 next piece is loaded. When not welding the load is very minimal maybe a few amps. During the welding process ( one or two seconds) the load climbs to about 370A on the 400A units and 200A on the 150A units. The measurements were taken with a clamp om amprobe so they are not 100% accurate. The load drops off before the amprobe can stabilize. I have been asked to back into plans to satisfy the city but I don't know how to figure these welders. They draw allot of current but it is intermittent and for very short periods of time. If I figure full current then the existing service (1200A) is undersized and its hard to tell an owner his service is to small and must be replaced when it has been working just fine for months. Anybody have any input??
I have a customer that has an existing installation of 4 welders. They are automated machines and they were built by the customer so there is no load information to go by. All are 480V 3 phase. Two are currently being fed with 400A breakers and two are being fed with 150A breakers. They way the process operates they weld for about 1 to 2 seconds then they are not welding for mabey 15 to 20 seconds while the 2 next piece is loaded. When not welding the load is very minimal maybe a few amps. During the welding process ( one or two seconds) the load climbs to about 370A on the 400A units and 200A on the 150A units. The measurements were taken with a clamp om amprobe so they are not 100% accurate. The load drops off before the amprobe can stabilize. I have been asked to back into plans to satisfy the city but I don't know how to figure these welders. They draw allot of current but it is intermittent and for very short periods of time. If I figure full current then the existing service (1200A) is undersized and its hard to tell an owner his service is to small and must be replaced when it has been working just fine for months. Anybody have any input??