Panel Schedule and Breaker Sizing for a Welding Shop
A welding shop adds a 200 A panel to serve two 60 A arc welders, a 30 A plasma cutter, and general receptacles. The electrician installs a 200 A main breaker and feeds the panel with 95 mm² copper. The welders have duty cycles of 60 percent and are cord-and-plug connected. The panel schedule lists each welder on a 60 A breaker with 8 mm² conductors to the receptacle. The plasma cutter is on a 30 A breaker with 6 mm² conductors. The owner wants all equipment running simultaneously during busy periods. The service is 120/208 V three-phase.
1. Evaluate the conductor and breaker sizing for the welders and the overall panel load.
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Welder circuits are sized based on the welder nameplate primary current and duty cycle, and the conductors and overcurrent device must be selected accordingly. A 60 A breaker with 8 mm² conductors is a mismatch: 8 mm² copper is not rated for 60 A, so the conductor is undersized for the breaker and the welder load. That is a fire hazard because the breaker will not protect the conductor.
The plasma cutter on a 30 A breaker with 6 mm² conductors is closer to correct, but I would verify the conductor ampacity and the receptacle rating against the nameplate.
The overall panel load must be calculated with the welders' duty cycle applied and with demand factors for the receptacles. Two 60 A welders plus a 30 A plasma cutter plus general load may exceed the 200 A panel when starting currents and simultaneous use are considered. I would require a load calculation and a revised schedule showing correct conductor sizes, breaker ratings, and duty-cycle-adjusted demand.
2. The owner insists all equipment runs at once. What is your compliance position and what corrective steps do you require?
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Simultaneous operation is a design basis, not an excuse to overload the panel. I would require the electrician to provide a load calculation that includes both welders, the plasma cutter, and the general receptacles at their full demand, with welder duty cycle applied as permitted. If the total exceeds the 200 A panel or the 95 mm² feeder ampacity, the design must change.
Corrective steps include replacing the 8 mm² welder conductors with conductors rated at least for the 60 A breaker, or reducing the breaker to match the conductor. The panel schedule must be corrected and posted. If simultaneous use exceeds capacity, the owner must either upgrade the service and feeder or accept an interlock or load management scheme.
I would not approve the panel as installed. I would issue a deficiency notice, require a corrected schedule and load calculation, and reinspect conductor sizes and terminations before energization.