ECN Forum Forums General Topics of the Trade General Discussion Area 1000 amp gfci breaker

Hi guys, haven't been on in a long time. Have a weird problem I'm on tonight. 1000 GE breaker serving a gym. At night when they turn off lights to the pool area. 4 circuits controlled by contactor. Controlled by one single pole switch. The 1000 main in the mdp trips. Controls and lighting circuits are in a 225 amp sub fed from mdp. It doesn't trip when turning lights on only when turning lights off

Any thoughts, I'm a little stumped