I am building a new computer for my friend and every time we try to turn it on the circuit breaker trips. Hes got an enermax liberty 620watt, i wanted to know if anyone has had a similar problem.

almost certainly a short-circuit (PCB touching chassis)

I thought about that so I tried starting it up with the mother board completely outside the case and it still trips the breaker.

try another PSU, I have had the exact same issue with my 8 month old Enermax Noisetaker II 600W. That ended up blowing up each time you pressed the on button, so I had to RMA it. With blowing up I mean that smoke and sparks would come out of it.

Seems like it's got to be a problem with the PSU itself, to me. With a PSU of that quality, any shortage on the DC side should get cut off at the PSU with a hard shutdown. The fact that the short gets to the AC side (and trips the breaker) says that the PSU isn't doing its job.

Does that make sense?

Had an interesting case with one of my psu's a 630 watt, were it would run perfectly and when i then turned it off it would trip the circuit breaker.
After a few times of that happening the psu died. RMA swapped it immediately.

The build quality on Enermax PSUs isn't very good, imo. I've heard numerous stories of them tripping stuff or just cutting out randomly. Verran is right, I wouldn't try to fiddle with it if I were you, RMA it.

OK...I didnt see anyone else ask....

do you mean the circuit on the PSU itself or the circuit breaker for the house or apartment where you are trying to plug the PSU into??

Ehh...nrg... Printed traces? Couldn't regular solider joints be more of a risk? ... maybe i don't know exactly what i'm saying though...