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UPS Output CB sizing

UPS Output CB sizing

UPS Output CB sizing

(OP)
Hello everybody
First of all please excuse my english.
We are installing a MGE Galaxy 5000 UPS rated 100KVA.
In the installation manual they recommand & 250A breaker in the input which i think is normal. But in the output they recommand a 120 A breaker. Is this breaker undersized ? or i'm the one who's missing something ?

I'm always working with the formule : Amps = KVAs x 1.55 so the output current would be normally 155 A.

Thank you in advance.

Amar OUZOU

RE: UPS Output CB sizing

After an outage, the input breaker will supply the load and the recharging current.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: UPS Output CB sizing

Care to tell us what the input and output voltage are?

No idea where you got that formula but it would only apply for a certain voltage and also for certain applications.

RE: UPS Output CB sizing

120A looks like a match for a 3-phase 480V output on a 100kVA unit.

RE: UPS Output CB sizing

(OP)
Hello and thank you for your ansewers.
The unit has an input/output voltage of 3 phase 380V.
@LionelHutz: The formula has a little error in it; it's AMPs = KVAs x 1.52 and it applies only for 3phase 380V.
S = sqrt(3)*U*I so I = S/(sqrt(3)*U)) this is where I calculated the formula and it' easy to keep in mind.

Thank you to all again.

RE: UPS Output CB sizing

Yes, it appears under sized. You won't be able to get 100kVA out of the UPS with that size of breaker.

Did you ask them why they recommended that size? Possibly, they gave that size based on a higher voltage, such as 480V or 600V.

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