3 phase education

[RRRDAD]

I need an air compressor for my sand blaster. I'm looking at a three phase compressor. Without getting real specific how big of breaker is required? Currently I have a 40 amp for my welder.

 

[Rock knocker]

I'm looking at a three phase compressor. Without getting real specific how big of breaker is required?

You're going to have to get specific.

 

[mm08822]

without getting real specific, you can only get a multitude of guesses as to what your answer could be.

Some basic q's to narrow down the possibilities:
do you have 3 phase power available?
Voltage
HP of expected ac motor
Inrush of motor during startup

 

[larry_g]

I need an air compressor for my sand blaster. I'm looking at a three phase compressor. Without getting real specific how big of breaker is required?.

Your motor size will dictate the breaker size, and the wire size, you need. In addition to the breaker you will need a motor starter, and a disconnect.

Bigger question is, Do you have 3 phase in your shop?

lg
no neat sig line

 

[Steve from Socal]

Without getting specific three phase motors use 1.73 amps per amp of single phase power. If the three phase motor is listed at 17 amps, it will need 29.41 amps not including losses in the conversion.

Steve

 

[Norcal]

If 3Ø is not available, then it opens a expensive can of worms, compressors do not do well with phase conversion equipment. Single phase motors are commonly available up to 10 HP, but be prepared to spend dough buy them.

 

[marinusdees]

It's not the size of the breaker. It's the price of three cans on the pole and the 3 phase service entrance. As noted, air compressors do not fare well with phase converters. Too much startup current is required.

 

[wyliesdiesels]

I need an air compressor for my sand blaster. I'm looking at a three phase compressor. Without getting real specific how big of breaker is required? Currently I have a 40 amp for my welder.

Unfortunately as others have said youre gonna have to get into the messy details.

Do u even have 3-phase service? I would assume so since youre asking about a 3 phase compressor.

If u do, the next detail is HP and voltage rating on compressor.

 

[wyliesdiesels]

without getting real specific, you can only get a multitude of guesses as to what your answer could be.

Some basic q's to narrow down the possibilities:
do you have 3 phase power available?
Voltage
HP of expected ac motor
Inrush of motor during startup

Inrush current doesnt need to be known and isnt a listed factor on nameplates. code allows breakers to be sized max 250% of NEC FLC current for this reason.

 

[RRRDAD]

Ok thank you. I did buy the thre phase compressor. My shop does have three phase so $200 for electrician and we should be blasting away.

 

[wyliesdiesels]

Ok thank you. I did buy the thre phase compressor. My shop does have three phase so $200 for electrician and we should be blasting away.

well wait a minute.

What type of 3 phase service do u have? Theres different types each with different voltages.

What is the voltage and HP rating on the compressor?

Im confused why youre asking any of this if u planned on using an electrician in the first place.

What was the point?

 

[manwithtools]

Hmmmm....Blast Off

 

[EOC_Jason]

Maybe he was thinking he could just plug it into the welder's receptacle (assuming it was 3 phase too)... Though I'm guessing he bought at least a 5HP compressor and has realized it's going to need to be hard-wired.

 

[Rock knocker]

Without getting specific three phase motors use 1.73 amps per amp of single phase power. If the three phase motor is listed at 17 amps, it will need 29.41 amps not including losses in the conversion.

Steve

That doesn't make a whole lotta sense

 

[Bert_]

That doesn't make a whole lotta sense

I think he's saying if no 3Ø is available, any type of converter will require approximately 1.73A of input power on 1Ø to run a 3Ø motor.

In this case it doesn't apply because the OP has 3Ø. Just look at the motor nameplate and size the breaker up to 250% of FLA

 

[mm08822]

[/b]

Inrush current doesnt need to be known and isnt a listed factor on nameplates. code allows breakers to be sized max 250% of NEC FLC current for this reason.

Excuse my missing carriage return on that last point. You are correct inrush value not needed for design/install. I know n/p only lists FLA's. My point was after the basics are out of the way, the ocp allowance for inrush on a motor ckt lets in another variable to answer his q.

Just b/c code says 2.5x max - doesn't mean you have to go to that value. If you have other breakers onhand under 2.5x, you may to to use them before buying another at ~2.5x.

Real point was, this q w/o specific info was like asking how much a car costs with no other detail.

 

[mm08822]

OP, So any info sources on the micro inverters failing everywhere?

 

[sberry]

This isn't for you, find something that plugs in to a common circuit.

 

[wyliesdiesels]

Excuse my missing carriage return on that last point. You are correct inrush value not needed for design/install. I know n/p only lists FLA's. My point was after the basics are out of the way, the ocp allowance for inrush on a motor ckt lets in another variable to answer his q.

Just b/c code says 2.5x max - doesn't mean you have to go to that value. If you have other breakers onhand under 2.5x, you may to to use them before buying another at ~2.5x.

Real point was, this q w/o specific info was like asking how much a car costs with no other detail.

Yes thats why i said MAX

OP, So any info sources on the micro inverters failing everywhere?

Hes ignoring u.

This isn't for you, find something that plugs in to a common circuit.

Huh? The OP has 3 phase...

And If the compressor is 3HP+ it cant plug into any circuit unless expensive pin and sleeve plugs are used.

 

[larry_g]

This thread is gives good reason to why I am reluctant to engage members with under 100 posts.

lg
no neat sig line