Feeding a UPS

Status
Not open for further replies.
Having an argument in the office. Assume a 600KVA UPS with a listed Full Load Amps of 761A. How do you size the OCP for this? 761 x 1.25 = 951.25A.

The recommended OCP from manufacturer is 1,000A. Can the breaker be sized at 800A which is the existing breaker in the field?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Having an argument in the office. Assume a 600KVA UPS with a listed Full Load Amps of 761A. How do you size the OCP for this? 761 x 1.25 = 951.25A.

The recommended OCP from manufacturer is 1,000A. Can the breaker be sized at 800A which is the existing breaker in the field?

I think you can put a 5 amp breaker on it if you want to. My guess is that it will trip a lot. Why would you argue with what the manufacturer suggests?
 

jap

Senior Member
Occupation
Electrician
Having an argument in the office. Assume a 600KVA UPS with a listed Full Load Amps of 761A. How do you size the OCP for this? 761 x 1.25 = 951.25A.

The recommended OCP from manufacturer is 1,000A. Can the breaker be sized at 800A which is the existing breaker in the field?

Yes, but why choke it ?


JAP>
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
Having an argument in the office. Assume a 600KVA UPS with a listed Full Load Amps of 761A. How do you size the OCP for this? 761 x 1.25 = 951.25A.

The recommended OCP from manufacturer is 1,000A. Can the breaker be sized at 800A which is the existing breaker in the field?

Is there a UPS already there that you are replacing?
You could use the 800 but you are limiting your UPS output.
 

ceb58

Senior Member
Location
Raeford, NC
Having an argument in the office. Assume a 600KVA UPS with a listed Full Load Amps of 761A. How do you size the OCP for this? 761 x 1.25 = 951.25A.

The recommended OCP from manufacturer is 1,000A. Can the breaker be sized at 800A which is the existing breaker in the field?

It would be a violation to not go with the Mfg. instructions. We use 18 Kw units for our communication buildings. The Mfg. chart states for a 18Kw unit it must be on a 125 amp breaker with #1 wire. When the tech. dose the start up he verifies that the breaker and wire is correct to their specks. if not he will not start the unit up.
 

abrace

Member
Location
New Hampshire
Occupation
Telecommunications Engineering
Having an argument in the office. Assume a 600KVA UPS with a listed Full Load Amps of 761A. How do you size the OCP for this? 761 x 1.25 = 951.25A.

The recommended OCP from manufacturer is 1,000A. Can the breaker be sized at 800A which is the existing breaker in the field?

I went through this a couple years ago with a new Eaton myself. This particular UPS had different output levels that were licensed all within the same hardware. UPS might be a 800KVA Frame, but may only come with 400KVA active. You need more output? Issue a PO, they give you a license key to plug in, and now it is a 600KVA UPS. Installation manual stated you could use different OCPDs and made suggestions based on output level.

Since it was replacing an existing UPS in our case, there was a desire to reuse the existing OCPD/feeder from the older UPS. Luckily I was able to convince the powers to be to spring for the feeder upgrade, because we would have ended up doing it 2 years later anyways. It is like an act of congress to just put the UPS in bypass around here, let alone ripping the feeder out and hoping you get it swapped before the batteries drain down and your datacenter goes dark.

Worth every penny to the UPS what it needs up front, IMHO. Much more costly to do it later.
 

ron

Senior Member
Most of the manufacturer circuit breaker sizing, especially for outputs, are recommendations, not requirements.

It's like a transformer, you have bottleneck the output if you want.

Remember that most molded case breakers are only rated for 80% current for >3 hours (non-continuous).
 
Status
Not open for further replies.
Top