Why does a 400 watt HPS ballast flip the breaker when it's turned off or unplugged?
 

Hey,

I have a 400 watt HPS light that feeds some plants in the basement
during the winter. When I unplugged the lamp in the morning (I
reversed the day/night cycle so it also keeps them warmer during the
cooler nights of winter), the circuit breaker would flip.

I also tried putting the lamp on a timer - which turned the lamp on
fine, but when it turned the lamp off - the breaker would flip.

Oddly enough, I did find that if I pulled (more like quickly snatched)
the plug from the wall - and I do mean quickly - the breaker would not
flip - and I was able to reproduce this consistently.

So, unless you know of a timer that snatches plugs from the wall to
turn them off - I was wondering if any of you knew what the problem
would be? What's the deal with the breaker flipping when the load on
the circuit drops - i.e. why isn't the breaker flipping when the light
turns on but flips when it turns off?? I'd like to solve the problem
while I have plenty of time before this winter...