I've got a 400a 480v 3ph GE Spectra Series breaker feeding the primary of a 112.5 kva transformer for temp power to jobsite (breaker feeds 125a fuses then transformer). The 400a breaker is gfci and sits in a hospital main switchboard. Pickups and gfi are set at minimum so as not to trip main. As the coordination study is not in yet, I'm afraid to 'up' the breaker settings.
My problem is that the transformer was shut down today and upon reenergizing the 400a breaker started tripping. This happened repeatedly under no secondary load (secondary conductors disconnected). After alot of time searching for a primary ground fault the breaker finally decided to hold.
I have used this type setup many times and have never had this problem. Inrush current to transformer? Ground fault? Any ideas?
BTW, I didn't have an ammeter.
Thanks in advance.
Brent
My problem is that the transformer was shut down today and upon reenergizing the 400a breaker started tripping. This happened repeatedly under no secondary load (secondary conductors disconnected). After alot of time searching for a primary ground fault the breaker finally decided to hold.
I have used this type setup many times and have never had this problem. Inrush current to transformer? Ground fault? Any ideas?
BTW, I didn't have an ammeter.
Thanks in advance.
Brent