Temporary 1000 KW generator wire sizing

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donw

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Arizona
Electrician is to replace a building's 800A SES and orders a temporary 1000W generator (that has a 3000A main circuit breaker) that he wants to hook up to the distribution panel to keep the building going while he replaces the SES. He wants to hook up the genset with (3) sets of 4/0 and a 4/0 GND. The City now wants me (the engineer) to draw up a plan showing fault current, etc. But to me, the 3000A gen breaker won't protect the 3 sets of 4/0 (although I realize that the generator will likely die if there is a short). How is this usually handled in a temporary situation? Surely they don't run 3000A worth of cable to a <800A load.
 
Presumably the conductors have to be protected by the 3000A breaker or you have to be able to use tap rules to consider them protected by the 800A breaker.

As I recall, taps are allowed to be pretty long out of doors...

-Jon
 
Yeah, I thought about tap rule, but the MDP is inside a warehouse area of the building. Presumably they would just lay the cable on the ground through one of the roll-up doors.
 
donw said:
Electrician is to replace a building's 800A SES and orders a temporary 1000W generator (that has a 3000A main circuit breaker) that he wants to hook up to the distribution panel to keep the building going while he replaces the SES.
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Do you maybe mean a 1000kW generator?
 
donw said:
I like the idea of adding an external 800A breaker.
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Don, the 1000kW generator has a 3000A breaker to accommodate the 208/120 or 240/120 delta configuration. It should also have an OC relay set at 1500A that is in operation in the 480V configuration and trips the breaker via shunt trip. The OC relay can be set at 800A for your project.
"Should" has blown up in my face more than once, so check with your generator vendor.
 
CapnBob65 said:
Don, the 1000kW generator has a 3000A breaker to accommodate the 208/120 or 240/120 delta configuration. It should also have an OC relay set at 1500A that is in operation in the 480V configuration and trips the breaker via shunt trip. The OC relay can be set at 800A for your project.
"Should" has blown up in my face more than once, so check with your generator vendor.
Click to expand...

Thanks for your comment. The electrician didn't mention a relay, so I do not know if there is one. The rental co. supplied us with an external 800A fused disconnect on request.
Thanks again.
 
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