RayV wrote:
Short story made long, my BIL's breaker feeding his pool house kept
tripping. The Black wire was causing the breaker in the house to trip
so I...

How was it causing the breaker to trip...was it a GFCI breaker? If it
was overloading the breaker through normal use, then changing conductors
isn't likely to help.

So now the pool house is 'grounded' via the conduit and the house is
grounded but now they are not sharing a ground.

Should the nuetral bar of the pool house now be bonded to the box
since the box doesn't have a ground running back to the main panel in
the house?

I believe so, yes. However I think you need to also drive ground rods.
You might want to check the local codes.

Chris