7 1/2 HP 1 Phase?

[EVOLVO]

My buddy and I are going to paint my car at his shop. He decided he wanted to upgrade his compressor. Amazingly he went on CL 3 weeks ago and found a NAPA 7 1/2 HP 220V 1 Phase 24 CFM unit with an Air Cel refrigerated drier for $2000!!
Both units appear to be nearly new. So we went down and loaded them up. The guy threw in a 4' x 4' x 2' electrostatic air cleaner for another $400, what a deal.
So the ? The shop has a 200 amp service that it shares with the upstairs apartment that has an electric stove and clothes dryer. We have a dedicated compressor 30 amp and a dedicated welder 30 amp circuits. The compressor manual says it needs an 80 amp breaker, does he have enough juice to use this unit? How do we figure it out?
Thanx, guys or gals

 

[ricleh]

A 40 amp breaker should be fine for a 7.5hp single phase 220 volt motor. That is what I am using and I have had no problems.

 

[moronmountain]

I'm no electrician, but I'm gonna guess you'd have to ask the peeps not to run the oven or dryer at the same time heh.

 

[moronmountain]

Also, I'd get the correct breaker for it. I mean if you have to buy one anyway.

 

[dttheliman]

One HP = 746 watts- therefore 5,595 watts
A little bit of Ohms law gets you w/v=a = 5595/220 = 25.4 amps

So the compressor runs at 25.4 amps , however start-up has to be factored hence the 80 amp requirement in the manual. (Change the existing 30 amp compressor breaker and cable accordingly)

IMHO you will be fine just don't cook, tumble-dry or weld when you start the new compressor
too many variables to be 100% accurate.

 

[Outlawmws]

My buddy and I are going to paint my car at his shop. He decided he wanted to upgrade his compressor. Amazingly he went on CL 3 weeks ago and found a NAPA 7 1/2 HP 220V 1 Phase 24 CFM unit with an Air Cel refrigerated drier for $2000!!
Both units appear to be nearly new. So we went down and loaded them up. The guy threw in a 4' x 4' x 2' electrostatic air cleaner for another $400, what a deal.
So the ? The shop has a 200 amp service that it shares with the upstairs apartment that has an electric stove and clothes dryer. We have a dedicated compressor 30 amp and a dedicated welder 30 amp circuits. The compressor manual says it needs an 80 amp breaker, does he have enough juice to use this unit? How do we figure it out?
Thanx, guys or gals

One HP = 746 watts- therefore 5,595 watts
A little bit of Ohms law gets you w/v=a = 5595/220 = 25.4 amps

So the compressor runs at 25.4 amps , however start-up has to be factored hence the 80 amp requirement in the manual. (Change the existing 30 amp compressor breaker and cable accordingly)

IMHO you will be fine just don't cook, tumble-dry or weld when you start the new compressor
too many variables to be 100% accurate.

200 A service and dedicated circuits, I don't see a significant issue...

You will however need to make sure your lines are suitable for the higher amperage requirements of the new compressor...

 

[larry_g]

Does the 80 breaker also have to run the drier? What is the amp draw of the drier?

lg
no neat sig line

 

[amolaver]

i've been looking at 7.5hp single phase units as well and all of them that i've examined say 40 amp breaker required. i wonder if the '80' amp reflects a double pole 40 amp (so 40 amp draw on each 120v leg). as others have said, make sure the wire running from the existing 30amp circuit is of correct size - 8ga MAY be alright, but i'd use 6ga especially if the run is longer than 50'.

larry_g's question is a good one though - what does the drier need? will you need a separate drop for it (and if so, how much power?)?

200a service should be plenty. stove and drier combined won't draw more than 100amps, so you've still got quite a bit of additional capacity. compressor+welder+range+dryer 'should' all be possible at once.

ahm

 

[W-Cummins]

The drier for that small size compressor will most likely plug into a standard 120v outlet.

William...

 

[rodm1]

Code for the 7.5Hp is 6 gage with a 60amp breaker. I'm using a 50amp breaker with no problems and much easier to find.

 

[Steve_P]

Code for the 7.5Hp is 6 gage with a 60amp breaker. I'm using a 50amp breaker with no problems and much easier to find.

50A breaker and 6ga here as well; haven't tripped a breaker yet.

 

[hdroadkingc]

50A breaker and 6ga here as well; haven't tripped a breaker yet.

I also have a 50amp on a 7.5hp single phase motor. No problems here.

 

[Charles (in GA)]

I ran #6 (three wires w/#10 ground) in conduit to a subpanel at the compressor, then continued the #6 to the motor starter on the compressor. I used a 60 amp breaker at the main panel and a 50 amp at the subpanel to supply the compressor. Never had a problem. Probably could have used #8 but this is a high load starting. My clamp on amp meter shows a peak (very short peak) of about 190 amps.

I don't have any problems. I think the motor data plate (Emerson 7½ hp) says FLA is 32 amps.

Charles

 

[EVOLVO]

Thanks to you all for the replies. I went from memory on the breaker sizes and had a senior moment for the compressor circuit, it's already 50 amp and nothing else is on it. The air drier is 120V, the clothes dryer upstairs is 220V and is on the welder circuit, which we're not using much right now. We started moving the old comp out and dismantled the new for transport. It weighs 750# and has to be moved around to the side of the shop across the lawn and installed into the stairway shed. Guess we'll try the 50amp circuit and see how it goes. Again, Thanx!!

 

[rlitman]

I also have a 50amp on a 7.5hp single phase motor. No problems here.

I have my 7.5HP single phase 240V compressor on a 30A breaker.
I ran 6 gauge wire from the panel to the disconnect switch, and from there to the starter box. I happened to have a 30A breaker handy, and installed it with the intention of changing it eventually. It hasn't tripped in the last two years yet.

The running current is listed at just over 27A IIRC, but you need to understand that breakers do not trip instantly at their rating. A 30A breaker will easily handle a 50+A starting current, so long as the compressor starts quickly. If your unloader fails (as an example), you will trip the breaker, but that's not necessarily a bad thing.

 

[IRREP]

The larger 80 amp is used for inrush current. You will have a voltage drop evey time that 7.5hp motor starts have seen 230v drop down 185v at startup. Huge problems when that happens.

 

[IRREP]

Keep the wires as short as possible.

 

[IRREP]

All air compressors use the full service factor (amps) listed on the motor FLA 32 x service factor 1.15 will pull 36.8 amps just before the pressure switch opens!

 

[IRREP]

If you dont need 7.5hp stay away from it, even if it's free. the added cost of your electrical install will be a deal breaker.

 

[IRREP]

Best IR 5hp 230V single phase is the 2340N5 for home owner garage, that pump has been in service for 30 years. Don't even think about trying to use it in a comercial building they Have 200-208 Volt service and will cook your motor NOT WARRANTY even if it gets replaced it will just burn up again.

 

[rlitman]

The larger 80 amp is used for inrush current. You will have a voltage drop evey time that 7.5hp motor starts have seen 230v drop down 185v at startup. Huge problems when that happens.

BS! The internal resistance of a 30A breaker is the same as an 80A.
Your point about the voltage drop is true to a point, but it is caused by too small wires. I'll come back to this.

All air compressors use the full service factor (amps) listed on the motor FLA 32 x service factor 1.15 will pull 36.8 amps just before the pressure switch opens!

Not the pressure switch. The centrifugal switch. And the service factor only comes into play IF your compressor isn't rated for continuous use (mine is, as are most 7.5HP compressors), or you changed the pulley ratios.

However, when a single phase motor starts, the centrifugal switch engages the start windings, which effectively doubles the current draw for a very short duration. So, if the FLA rating of a motor is 27A, the start current is more like 54A. That's not really enough to trip a 30A breaker through the magnetics (which depending on the breaker is usually between 2x and 10x the rating).

Now, you need to understand that the FLA rating on a motor is based on the voltage being correct. If the voltage drops, the current will INCREASE. So if I were to have run a 10 gauge wire on that 30A circuit, the voltage drop caused by the high starting current could cause the current to rise to the level needed to trip the breaker. I attribute my success to having 6 gauge wire for the entire run (which is very short as well).
Not only would having too small a wire cause a voltage drop causing a current increase, which would trip my breaker, the current increase also causes additional heating in the motor's coils. This will kill the motor eventually.

 

[Charles (in GA)]

If you dont need 7.5hp stay away from it, even if it's free. the added cost of your electrical install will be a deal breaker.

Apparently you didn't read the original post. The OP has already acquired the compressor.

There are lots of 7½ hp compressors in use. The electrical is NOT a "deal breaker" at all. Merely a different circuit breaker, and heavier wire and disconnect if used. Its simply part of what is necessary to have a large quantity of compressed air available to you.

How much extra cost do you think an electrical install for 60 amps over 30 or 40 amps is anyhow???? $25? $50? $100? How much do you think a decent working 7½ hp 80 gal two stage compressor costs anyhow?

Charles

Charles

 

[sberry]

This is a heavy well built comp it appears and their draw is a bit above many of the box store models. 8 or better wire and 50 or larger breaker, would probably see if that worked and wouldn't hesitate to go with 60 if I had one on the shelf, was installing new and had to buy one.
FWIW, about 6A 230 to make 4 cfm in a 2 stage comp, these days it usually a little less, probably closer to 5, incoming voltages way above when 220 was standard. This is a pretty respectable unit. People throw in a lot of stuff, it can be one of the benefits of shopping,, they usually wait to see if they like you and don't haggle the price, its a reason I often don't blink and give the asking,,, after the fact they come with the goodies,,, here,, you might as well have this etc.

 

[EVOLVO]

I know there have been complaints about folks not coming back to a thread to report the outcome so............we got the compressor installed and wired up using a 40 amp breaker and #8 wire. Works like a charm. We had to replace a defective pressure switch with a new one from Grainger, off @150# on @120# and when it comes on it only runs for 40-45 seconds before shutting back off, really nice. We got the Air Cel drier online and working, too. Had a little problem with that as well, the timed blow down solenoid had dirt on the seat and wouldn't shut off, simple to clean and now it works great! I talked to a tech at Air Cel about this, he knew what the problem was before I even finished explaining what it was doing. He also looked up the serial number and told me the unit was one of the last all copper units they built in 2005! The equivalent unit today retails for $2600!! I guess we done good. Thanx again for all the help