Commercial compressor 90 amps

[jim dungar]

If your service is 240/120V 3 Phase 4 wire delta (also called various nicknames like high-leg) you can easily go straight to a 240V 3-phase motor/machine, without needing any phase convertor or transformer.

You will need a 240V delta - 208Y/120V transformer to feed your new panel.

 

[hbiss]

Please, forgive me of my ignorance. There are two 208 3 phases, correct? I’ve installed a 208 Y panel for a customer before and circuits to machines. But this store panel is definitely 208 high leg delta. Every third space is 208 to ground.
How do I know which 208 this compressor needs? Or do they come with option to change on site?

How about going to the 100A panel and measuring at the main lugs the voltages phase to phase (A to B to C) and telling us what you have? THAT'S what the compressor will run on! And that voltage is what you will use to determine the motor, OCP and starter.

Forget all this other nonsense.

-Hal

 

[LarryFine]

How do I know that my 240 v Delta (with the 208 v high leg) is the right 3 phase for this compressor?

There is only one kind of delta, but which conductor, if any, is grounded can vary.

All that matters to any load that does not require a neutral is the line-to-line voltage.

Just make sure the motor is rated to run on a 240v 3ph supply and you'll be golden.

 

[kwired]

That is not sufficient to meet the NEC.
You need motor sizes or total machine amps. You need your nominal supply voltage system.

He has simply sent you a picture of a OCPD manufacturers selection chart.
You need to see the compressor manufacturer's data, either a nameplate or catalog page.

You definitely do not have a 208V delta. You may be using a local slang term for a standard high leg 240/120V 3phase 4 wire system.

Square D's charts I've had all put NEC FLA values on the charts. I think that the one he posted is Square D. The Thermal magnetic breaker on that chart is manufacturer's recommendation and I have almost never had a problem using the breaker they recommend. Having a rather short circuit length and high available fault current could possibly result in magnetic trip during starting though.

 

[kwired]

Thank you, I asked him again for a nameplate, and he responded “it is not built yet “
How do I know that my 240 v Delta (with the 208 v high leg) is the right 3 phase for this compressor? Can I assume it is the correct power source since there are two existing compressors powered from 3 phase breakers in this panel? Other machines on a another job required me to install a 3 phase 208 Y panel. Thank you so much.

If it is not built yet have they been informed of the system voltage? They probably will build it to that, presuming you correctly told them what you have.

Don't say anything about 208, that can be misleading like it appears to have been for you. From what you have mentioned all they need to know is you have 240 volt delta supply. If they build it for that it will work for you with no transformations necessary.

 

[jim dungar]

Square D's charts I've had all put NEC FLA values on the charts. I think that the one he posted is Square D. The Thermal magnetic breaker on that chart is manufacturer's recommendation and I have almost never had a problem using the breaker they recommend. Having a rather short circuit length and high available fault current could possibly result in magnetic trip during starting though.

My memory tells me, the FLA on the motor data calculator are simply the NEC values, they do not represent any real world value. The motor data calculator currents used to select the thermal units (overload protection) are from averaging data from several manufacturers, so again it is not an actual real world value. For the most part the data on these calculators has not changed for decades
The short circuit protection was chosen based on magnetic pick up points of roughly 10x the NEC full load current, in order to coordinate with the thermal unit chosen at 6x for 20 secs.

 

[kwired]

My memory tells me, the FLA on the motor data calculator are simply the NEC values, they do not represent any real world value. The motor data calculator currents used to select the thermal units (overload protection) are from averaging data from several manufacturers, so again it is not an actual real world value. For the most part the data on these calculators has not changed for decades
The short circuit protection was chosen based on magnetic pick up points of roughly 10x the NEC full load current, in order to coordinate with the thermal unit chosen at 6x for 20 secs.

NEC values are what you are supposed to use for selecting conductor ampacity though as a general rule for motor circuits. If this is a simple air compressor with just a single motor for load then this sort of applies. If it is multiple motor or combination load piece of equipment with single supply circuit then appliance nameplate is what you need to be looking at for branch circuit information.

 

[electroman00]

There are many types of compressors used...we need a picture of the unit/s and the placards on each.
Tire/Car dealers have dual compressors on one platform and have control systems that will startup based on demand.

I don't care what anyone says or docs you are given...

Pics of what is on the placard is what counts and nothing else matters.!

Pictures of the panel would be necessary as well !!
2 pics...one of main breaker and one of inside wiring.
aka a PICTURE is worth a 1000 words !!

You're asking to diagnose in the blind for us all...which leads to a stream of bull as seen above!

This isn't a game of who can guess the best solution...this is called real world LIFE SAFETY aka Electricity!
An overloaded panel can easily cause a fire, fires can kill and/or explode in someone's face...!!

Following proper diagnostic procedures leads to the correct solution/s and safety!!

Throwing Poo at the wall here isn't the proper diagnostic procedure/s!

As you have confessed to not knowing and lacking experience !!

My best advice is to leave it to a Trained & Experience Professional in the Industrial/Commercial Electrical/Mechanical Business!

Have a good day...

 

[Frank DuVal]

How can the panel be overloaded IF the breaker feeding it is properly sized, in this case 100 amps? I rarely ever see a panel where the breakers add to less than the main rating.

Compressors are just motors that turn on and off.

I understand the need to prewire for when the compressor is built and delivered, unless the compressor sits next to the subpanel. All you can do is tell the store you will prewire to what the manufacturer says, and if it is wrong, then that is going to be more money. The good news is you can plan on #6 and a 90 amp breaker and go down on fuse and breaker size if the nameplate is different.

Sounds like a screw compressor. Hope it is, as many have VFD for control.

 

[ptonsparky]

How can the panel be overloaded IF the breaker feeding it is properly sized, in this case 100 amps? I rarely ever see a panel where the breakers add to less than the main rating.

Compressors are just motors that turn on and off.

I understand the need to prewire for when the compressor is built and delivered, unless the compressor sits next to the subpanel. All you can do is tell the store you will prewire to what the manufacturer says, and if it is wrong, then that is going to be more money. The good news is you can plan on #6 and a 90 amp breaker and go down on fuse and breaker size if the nameplate is different.

Sounds like a screw compressor. Hope it is, as many have VFD for control.

Exactly. Most likely everything will work fine. Taking current and voltage readings once it’s up and running will setup the next stage of work, if needed.

 

[Jraef]

Every third space is 208 to ground.

That is the hallmark of a 240/120V delta 3 phase 4 wire system. There is no such thing as “208V high leg delta”, that does not exist. The customer is telling you this because they are ignorant. In a 240/120 delta 3ph 4wire system, you will MEASURE 208V from B phase to Neutral (or ground), but that is just a “trick” of the math. You will measure 240V phase to phase, which is all you care about on 3 phase loads.

FORGET that the 208V issue exists! Too many people get all hung up on that issue, yet it is TOTALLY IRRELEVANT to your 3 phase loads. It (208V) only really matters in the case of 1 pole breakers, which is why you usually can’t plug them in to B phase. The only relevant issue is that if you want 240V SINGLE phase (2 hots) then you must use “fully rated” 240V 2 pole breakers, as opposed to cheaper versions that are 120/240V rated.

So back to YOUR situation, they need to make sure that they buy a compressor RATED for 230V 3 phase, NOT 208V. At 10HP, the motor will NOT likely be rated for 208-230V, the compressor mfr will likely give them a motor rated for 200V, which is NOT OK for using on 240V.

 

[drcampbell]

... Don't say anything about 208, that can be misleading like it appears to have been for you. From what you have mentioned all they need to know is you have 240 volt delta supply. ...

Don't even say "delta". Just say there's a 240-volt 3-phase circuit available (after verifying that) and they need to build the compressor around a 230-volt 3-phase motor.

 

[kwired]

That is the hallmark of a 240/120V delta 3 phase 4 wire system. There is no such thing as “208V high leg delta”, that does not exist. The customer is telling you this because they are ignorant. In a 240/120 delta 3ph 4wire system, you will MEASURE 208V from B phase to Neutral (or ground), but that is just a “trick” of the math. You will measure 240V phase to phase, which is all you care about on 3 phase loads.

FORGET that the 208V issue exists! Too many people get all hung up on that issue, yet it is TOTALLY IRRELEVANT to your 3 phase loads. It (208V) only really matters in the case of 1 pole breakers, which is why you usually can’t plug them in to B phase. The only relevant issue is that if you want 240V SINGLE phase (2 hots) then you must use “fully rated” 240V 2 pole breakers, as opposed to cheaper versions that are 120/240V rated.

So back to YOUR situation, they need to make sure that they buy a compressor RATED for 230V 3 phase, NOT 208V. At 10HP, the motor will NOT likely be rated for 208-230V, the compressor mfr will likely give them a motor rated for 200V, which is NOT OK for using on 240V.

If it has a general purpose motor in it it can very well be rated 208-240. If it is a OEM motor then it may be more likely to be a 200 volt rated motor if designed for a 208 system.

A screw type compressor from my observations is more likely to be an OEM motor especially at only 10 HP. I know of 40 and 50 HP units that have general purpose motors in them though.

Every reciprocating compressor I have seen that is over ~5 hp is usually a general purpose motor. Single phase and under 5 HP is usually those special marked motors that are for example a 3 hp build but marked as a 5 even though that is peak available for limited time.