1200 amp 208 volt main breaker tripped

[Fordean]

Wow so all that 400A house panel had was the earth as a EGC?
You might check voltage drop under full load at a peak time the W/ POCO present, sometimes they can 'notch up' the transformer changer taps, that would drop the amps some.

What problems can this cause? conduit is underground. Told them we need to pull out the aluminum 8 - 250kcm and install new wires with ground. Can we dig a trench next to 4 inch and run a 1 inch and install a ground in it. So not to cut up 8-250's?

 

[hillbilly1]

What problems can this cause? conduit is underground. Told them we need to pull out the aluminum 8 - 250kcm and install new wires with ground. Can we dig a trench next to 4 inch and run a 1 inch and install a ground in it. So not to cut up 8-250's?

Being a house panel, does it feed the parking lot lighting? If so, it can be a big problem. A fault to the metal poles will most likely not clear, because of the high resistance of the ground rod(s) and pose an electrocution hazard to anyone that touched them.

 

[Fordean]

Being a house panel, does it feed the parking lot lighting? If so, it can be a big problem. A fault to the metal poles will most likely not clear, because of the high resistance of the ground rod(s) and pose an electrocution hazard to anyone that touched them.o

Ok will verify

 

[mayanees]

Those are factory-default breaker settings. Ideally you should find out what's upstream of this breaker and adjust for coordination. But without that I'd at least come off the factory defaults.

 

[Fordean]

Those are factory-default breaker settings. Ideally you should find out what's upstream of this breaker and adjust for coordination. But without that I'd at least come off the factory defaults.

I callec square d they said 4or 5 for instantaneous trip Dial up from 1.5 settings I have picture above

 

[Todd0x1]

If it trips again maybe consider setting up a logger on it. I wonder if the load isn't 'diverse enough' when its cold and this is a simple case of overload.

 

[tortuga]

Wow so all that 400A house panel had was the earth as a EGC?

What problems can this cause? conduit is underground. Told them we need to pull out the aluminum 8 - 250kcm and install new wires with ground. Can we dig a trench next to 4 inch and run a 1 inch and install a ground in it. So not to cut up 8-250's?

I'd say this is a pretty big issue see 300.3(B), its an illegal installation, if there is a ground fault in the 400A panel and the earth is acting as the return conductor, then the ground fault may never clear (worst case).
There is something in 300.3(B)(2) and (3) that might help.
either way you probably need to get AHJ involved and approve the fix.