QTY=3 of 3/0 CU on a 200amp brkr (if fused, use time-delay). That's what I would do! Of course, separate breakers, and I would also consider the available power in this building. If there's no interlock on these compressors to avoid them starting simultaneously, you could have a pretty sizeable "bump" on the CDP feeding them! The manufacturer may even have something already in place to avoid this from happening.

 

I’m redoing an existing install.

Currently we have a 600A OCPD feeding into a Tap Box then down to (3) 200A disco’s

The facility wants individual breakers from the main switchgear to each unit.

The facility had prior notes and a 225A OCPD was listed to each unit, I’m trying to figure out why.

 

A compressor that size will almost certainly have some sort of a soft-start so surge current won't be an issue.

3/0s and a 200 amp breaker should be just fine.

To find the actual minimum wire size, we'd need to know either the motor HP or the motor full-load amps. I suspect you could go to 2/0 or maybe even 1/0 with a 200 amp breaker.

 

A compressor that size will almost certainly have some sort of a soft-start so surge current won't be an issue.

3/0s and a 200 amp breaker should be just fine.

To find the actual minimum wire size, we'd need to know either the motor HP or the motor full-load amps. I suspect you could go to 2/0 or maybe even 1/0 with a 200 amp breaker.

The motor amps are called out on the ID plate. They give you a machine amperage plus the motor separately, so the load at 125% is around 140A.

 

Ask to see the owner's Electric bill. See if there's a separate charge for Demand.. Some Utilities have it, some don't.
It's an amount charged by total Demand in 15 minute periods. This can be reduced by installing time delays on two of the three Compressors. That way all three don't turn on at the same time.

There may also be a charge for Power Factor. This is current lead and lag. The Power Factor can be corrected by installing Capacitors on the Service Entrance. On one job, I saved the owner $800/month by installing capacitors. It ended up he didn't save anything, because he wife bought a Cadillac Escalade with the savings.

 

Manufacturers' nameplate states "field supplied" 175 amp FUSE, doesn't list a circuit breaker. Why would you want to install something other than what is listed on the nameplate? I wouldn't deviate from the listed fuse size. OEMs usually know what is best to protect their equipment.

 

I’m looking to run (3) of these compressors.

Name plate 120FLA. Fuse 175A

Im figuring

3x3/0 on 200A breaker per unit.

Am I doing this right ?

The wire and OCPD size is calling lower than I figured but wouldn’t I upsize the wire if I upsize the OCPD to the next size for a compressor? I could be wrong on this.

Manufacturers' nameplate states "field supplied" 175 amp FUSE, doesn't list a circuit breaker. Why would you want to install something other than what is listed on the nameplate? I wouldn't deviate from the listed fuse size. OEMs usually know what is best to protect their equipment.

Disconnects could be fused, I don’t know.

The facility is strict and we couldnt openi things up on a walk-through.

 

I’m looking to run (3) of these compressors.

Name plate 120FLA. Fuse 175A

Im figuring

3x3/0 on 200A breaker per unit.

Am I doing this right ?

The wire and OCPD size is calling lower than I figured but wouldn’t I upsize the wire if I upsize the OCPD to the next size for a compressor? I could be wrong on this.

They really dotted all of the i's for you. They are even specifying the class of fuse, so that is going to be something to consider when you buy your disconnects. Not every disconnect is set up for J-class fuses - most are set up for RK5 fuses. Just specify to the supply house that you are running J-class fuses and you'll be fine. Three sets of AJT 175's, and I would run #0/3-3 ACWU (aluminum), because they are specifying the full load for the entire device. The motor is less, so the actual required amperage is around 140A. If you are addicted to copper than I would run #0-3C teck or T90 in conduit or whatever.

That's what I would do, anyway.

 

I’m looking to run (3) of these compressors.

Name plate 120FLA. Fuse 175A

Im figuring

3x3/0 on 200A breaker per unit.

Am I doing this right ?

The wire and OCPD size is calling lower than I figured but wouldn’t I upsize the wire if I upsize the OCPD to the next size for a compressor? I could be wrong on this.

They really dotted all of the i's for you. They are even specifying the class of fuse, so that is going to be something to consider when you buy your disconnects. Not every disconnect is set up for J-class fuses - most are set up for RK5 fuses. Just specify to the supply house that you are running J-class fuses and you'll be fine. Three sets of AJT 175's, and I would run #0/3-3 ACWU (aluminum), because they are specifying the full load for the entire device. The motor is less, so the actual required amperage is around 140A. If you are addicted to copper than I would run #0-3C teck or T90 in conduit or whatever.

That's what I would do, anyway.

Those are the disconnects we are using.

We are just deleting the 600A tapped feed and running (3) 200A feeds. Using same disco’s.

 

Our three Atlas 75's have breakers for each,...

 

Our three Atlas 75's have breakers for each,...

I don’t think I’ve ever seen a 4 wire Compressor, yet yours and Wrongunns show a wye feed.

What is the neutral used for?

 

We recently completed an Atlas Copco unit. Called for Type T fuses. Those were a nightmare to get. We also had to adjust the disconnect terminals and install a mounting kit.

Class T sucks, but they're not as bad as semiconductor fuses. Just bend over and grab your ankles...

Those are the disconnects we are using.

We are just deleting the 600A tapped feed and running (3) 200A feeds. Using same disco’s.

Same disconnects? Are they already set up for class 'J'? You might need new guts.

 

We recently completed an Atlas Copco unit. Called for Type T fuses. Those were a nightmare to get. We also had to adjust the disconnect terminals and install a mounting kit.

Class T sucks, but they're not as bad as semiconductor fuses. Just bend over and grab your ankles...

Those are the disconnects we are using.

We are just deleting the 600A tapped feed and running (3) 200A feeds. Using same disco’s.

Same disconnects? Are they already set up for class 'J'? You might need new guts.

We aren’t changing anything. This is an existing setup.

It’s fed from (1) 600A breaker. We are just running (3) raceways from switchgear breaking it off into (3) separate breakers.
Everything stays as is.

 

If you aren't changing anything then why are you asking the question?

 

Guess they want a neutral everywhere, probably some safety goings on,...