UPS upstream breaker sizing

[ethode_apc]

So we're running into a really interest issue.

1) We have a Symmetra PX 80kw with the 480v PDU (pd80g6fk1)

2) The PDU says 160 amps input

3) Your website says max 135 amps (http://www.apc.com/shop/us/en/products/InfraStruxure-PDU-80kW-480V-208V-W-MBP/P-PD80G6FK1-M)

4) The manual says 150 amp up stream breaker.

All of these amp ratings seem to contradict each other; can someone explain?  Even at a power factor of .80 (assumed) 80kw would need 100kva to service that 80kw which makes sense according to the name plate, but that also means that 120 amps is it's maximum.. None of this makes sense. haha

Thanks in advanced!

[BillP · Accepted solution]

Hi,

The transformer in that PDU is a 112.5KW not 100 or 80k and requires the 150A (per notes should be 100% rated 150A or 80% 175A)
kw x 1000 / V x pf x 1.732
112,500 / 480 x .982 x 1.732
112,500 / 816.39 = 138A
138 x 1.25 = 172.5A (closest standard size CB is 150A as to not over size for safety)

The Certified Electrician's Instruction list the breaker at 150A 

http://www.apcmedia.com/salestools/ASTE-6YWKJE/ASTE-6YWKJE_R0_EN.pdf?sdirect=true

Its common that Schneider will use a slightly larger isolation transformer in the PDU products. Over sizing of the input transformer is better than using a K13 rated transformer to handle harmonics. However, the PDU is only rated for 80kW therefore, 150A input CB is required.

[ethode_apc]

Thanks Bill. Down the road we assume that we're putting in a "B" UPS unit and it will be 225kw instead of the 80kw we have now and we will decommission this current UPS and upgrade it as well.

While we're finishing up the panel board, can tell me upstream breaker size we would need to cover a future 225kw UPS?

Thanks!

[ethode_apc]

Was able to get ahold of an APC rep... Wanted to answer this for future readers

A 225kw UPS would windup with a 350amp breaker and 250kw would be 400amp.