question of sizing LV switchgear
question of sizing LV switchgear
(OP)
Can anyone help - I am upgrading a building supply to 1000KVA at 400V and installing new switchgear and a standby generator. The client has a spare generator rated at 1250KVA. The electrical contractor says the size of the main switchgear should be based on the rating of the generator not the incoming power supply which means we need 2000A rated incoming MCCB's (generator amps = 1800A max).
I don't agree with this as I think the generator can't supply more than the actual building load - which means I can use MCCB's rated at 1600A. Is this ok?
I don't agree with this as I think the generator can't supply more than the actual building load - which means I can use MCCB's rated at 1600A. Is this ok?






RE: question of sizing LV switchgear
A good engineering practice is to double check the interrupting capacity of the breaker for the worst-case scenario (utility vs. genset) and also check the generator capacity to move all connected loads
RE: question of sizing LV switchgear
RE: question of sizing LV switchgear
Also if you apply utiltiy company logic, they normally undersize the supply transformers and if need be they do not mind running the transformer overloaded by 10-15% for long periods of time (more true for oil insulated units).
I personally do like to see the main service breaker or switchboard loaded anywhere near 80%, its too close for comfort and short sighted. You do not want to be making changes to the main service because a slight addition to a faciltiy. I would vote for 2000A breaker with adjustable trip unit.
Incremental cost may not be too significant. Do not lose sight of good engineering/ buisness sense in a zeal to make a technical point to a contractor. We engineers are too often guilty of that.
No offence intended.
RE: question of sizing LV switchgear
RE: question of sizing LV switchgear