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I have a subpanel feeding off a 50 amp breaker. The subpanel contains a GFCI 50 amp breaker which is connected to a new 32amp spa heater. When I flip the GFCI breaker on for the heater, it immediately trips the main 50. Nothing else is connected to the subpanel and the GFCI itself doesn’t trip. I have pulled 40amps from this subpanel while charging my EV.

The spa heater is a Balboa VS501Z.

Any thoughts on what I can check?

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  • Has it ever worked on the new spa? It sounds like you have a direct short and the spa is defective. Or it may be just the with manufacturing tolerance differences of the breakers: the breaker in the main panel is slightly more sensitive and trips first. Also, and I'm speculating a bit here, not all GFCI devices have over-current protection (most outlets don't), it's a common miss-conception. Not sure about your spa gfci breaker. Hopefully one of the big 3 will chime in and help. But in any case, I think you've got a defect in your spa or it's badly miss-wired. – George Anderson Jan 16 at 15:01
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Check to make sure your spa heater is configured correctly for 240V operation

The Balboa VS501Z uses a solid-state control board that is configurable for 120V or 240V operation; however, when in 120V mode, it requires a hardwire jumper from neutral to a L2 (red) connection on the board to configure it, as per the manual. If that jumper is present on a VS501Z connected to a 240V supply, your breaker will trip immediately due to the jumper being a dead short from L2 to N, as you are observing. (If you're wondering why the breaker in the main panel trips but the breaker in the spa box doesn't trip, that's because what you have is basically a race condition between the two breakers, and whichever wins is determined by factors that are beyond our effective control.)

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  • Thank you ThreePhaseEel! The jumper cable was connected for a 120V setup. It’s now running great! Sorry that I’m a newbie and my upvote doesn’t reflect here. – paulg Jan 16 at 20:29

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