JOE.G
Well-known member
Guys How Many amps does a 80 Gal 220 V 5 to 7.5 HP Air compressor usally use?
220 Air Compressor Amp Question.
- Thread starter JOE.G
- Start date
EOC_Jason
Well-known member
There is a difference between startup amps & running amps. Also depends on the PSI... The higher the pressure, the harder the pump & motor have to work, the more amps it will draw. You can literally clamp a meter on and watch as the pressure builds up your amps will increase.
ez-duzit
Well-known member
My 7.5 hp compressor motor says 30 amps @ 220 volts.
Gary S
Well-known member
"Usually uses" isn't nearly as valuable to you as the Amperage numbers stamped on the motor nameplate. Start there and get the manufacturer's ratings.
here is a chart you can go by
CHART
on edit
As a "rules of thumb" amps horsepower rating can be estimated as
115 Volts motor - single-phase : 14 amps/hp
230 Volts motor - single-phase : 7 amps/hp
230 Volts motor - 3-phase : 2.5 amps/hp
460 Volts motor - 3-phase : 1.25 amps/hp
lg
no neat sig line
CHART
on edit
As a "rules of thumb" amps horsepower rating can be estimated as
115 Volts motor - single-phase : 14 amps/hp
230 Volts motor - single-phase : 7 amps/hp
230 Volts motor - 3-phase : 2.5 amps/hp
460 Volts motor - 3-phase : 1.25 amps/hp
lg
no neat sig line
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RickP
Well-known member
ez-duzit said:
My 5 hp motor says 21 amps @ 240 volts.
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pattenp
Well-known member
By the NEC for sizing circuits you use the HP on the motor data plate, 5HP is 28A @ 230V and 7.5HP is 40A @ 230V.
I am wiring everything up, And I don't have the Compressor narrowed down yet. SO I want to get a rough Idea,
This is what I have,
I have a 220 run with 12 2 or 12 3 Romex with a double 20 Amp Breaker
then I have a much larger 220 with a 50 Amp Breaker.
I am not a electrical guy someone ran this for me, one was sup to be for a compressor and one for a welder.
This is what I have,
I have a 220 run with 12 2 or 12 3 Romex with a double 20 Amp Breaker
then I have a much larger 220 with a 50 Amp Breaker.
I am not a electrical guy someone ran this for me, one was sup to be for a compressor and one for a welder.
wyliesdiesels
Well-known member
The wire for motor circuits is sized at 125% of FLA of the motor, so #12 Romex would be too small for those motors!!
EDIT: Individual #10 THHN conductors would work for the 5hp and #8 THHN for the 7.5hp!
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ez-duzit
Well-known member
WAY too small for 7.5 hp.
wyliesdiesels
Well-known member
All depends on the size of wire! Welder circuits are allowed to be undersized. Can u see what size the wire is?
ArmyVW_GuyInTX
ALLIANCE MEMBER
I have an IR 7.5 HP/80 gallon that pulls 28amps on start-up according to the owner's manual.
I ran #6 awg to a sub panel and drilled through the wall to the compressor (outside on cork/rubber blocks but in an enclosure) and have a 30amp breaker for it years ago.
I ran #6 awg to a sub panel and drilled through the wall to the compressor (outside on cork/rubber blocks but in an enclosure) and have a 30amp breaker for it years ago.
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wyliesdiesels
Well-known member
#6 is a little overkill!
RickP
Well-known member
JOE.G said:
Yes, the 50 amp circuit would work for the 7.5 hp.
You'd probably need a 40 amp for the 5 hp, but that 12 ga cable is too small.
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I am looking at these two,
http://www.sears.com/shc/s/p_10153_12605_00916477000P
http://www.tractorsupply.com/en/store/ingersoll-randreg;-5hp-air-compressor-80-gal
I am unsure on the wire size on the 50 amp circuit but i can find out.
http://www.sears.com/shc/s/p_10153_12605_00916477000P
http://www.tractorsupply.com/en/store/ingersoll-randreg;-5hp-air-compressor-80-gal
I am unsure on the wire size on the 50 amp circuit but i can find out.
wyliesdiesels
Well-known member
If the wire was sized based on a welder using the circuit, the wire might be too small as circuits feeding welders are allowed to be reduced in size!!
pattenp
Well-known member
For those comps I'd use #8 on a 40A breaker. I'd assume the 50A circuit you have has #6, but if it's marked as a welder outlet it could have a smaller wire.
ez-duzit
Well-known member
Perhaps I missed it but wire size depends on the distance run as well as the amps.
pattenp
Well-known member
Distance does come into play but usually at distances greater than 100'. So for typical circuits within a house distance is not a wire size adjustment issue.
ez-duzit
Well-known member
wyliesdiesels
Well-known member
Sorry, but I beg to differ.
Nice try but thats for 12v DC wiring which is a whole different animal than AC wiring!
ddawg16
Well-known member
If that table 'was' for AC.....none of us would be able to have anything larger than 100A at our house..
There are actually two tables for AC wire current....one is referenced to AC Transmission....the other is chassis wiring (control panels).
And then you have the NEC table for AC power distribution....which is sort of in between the above 2.
ez-duzit
Well-known member
Oops! Serves me right for choosing it because of the pretty colors.
edit: 3-phase.
Found calculators for 1 phase but no charts. Huh.
3-phase
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pattenp
Well-known member
I'm not following what you want to beg to differ about? I didn't say wire size didn't need to be adjusted for distance. I agree that it does. I'm just saying over sizing wire for voltage drop typically doesn't come into play until you reach lengths of 100' or more for the average household circuit and even then it depends on the anticipated loads.
ez-duzit
Well-known member
Yeah, I was having difficulty accepting the need for the same size wire to run 40 amps 6 inches as 100 feet.
I used #8 on a 40A breaker. Manual stated min of 30A breaker for a 30A draw at startup. Motor plate reads 23A for running 5hp. Mine is http://www.aircompressorsdirect.com/Industrial-Air-IV5248069-Air-Compressor/p3706.html sears compressor unit looks the same.
RickP
Well-known member
Good call -- for an extreme case (like a large motor or a long wire run).
But for the OP (who hasn't bought a compressor yet), I think chances are pretty good that the 50A circuit will be perfect for a 7.5 hp compressor. He'll definitely need to check his wire size to be sure it wasn't sized for a welder, but unless it's an extreme case, that 50A circuit should be adequate for a 7.5 hp motor (or less).
I say this because Joe's friend probably ran 6 AWG cable for that 50 amp circuit, if not, then it's gotta be 8 AWG (because it's "much larger" than the #12 Romex). A big box compressor will probably use a motor with FLA of about 32A -- post #9 here: http://www.garagejournal.com/forum/showthread.php?t=131410 -- which means 125 percent of the FLA is going to be right at 40A, so that would need 8 AWG cable. If he hardwires the comp to a disconnect, then I believe the NEC allows a 50A breaker on that circuit.
Please let me know if I have any of that wrong, because I'm hoping I can hardwire my 5 hp comp with 10 AWG cable and a 40A breaker.
Thanks,
Rick
pattenp
Well-known member
If using romex, #10 NM-b is 30A max and #8 NM-b is 40A max. Being hardwired has noting to do with the breaker size. If you use THHN in conduit then #10 THHN is 35A and #8 THHN is 50A. The difference is romex is to be sized at 60 deg.C and THHN is sized at 75 deg.C.
RickP
Well-known member
pattenp said:
Okay, now I'm confused -- I thought the NEC allows the breaker to be oversized (compared to a smaller wire size) for a hardwired motor, to allow for startup current draw???
So for a normal circuit, I would use a 30A breaker to protect 10 AWG cable. But for a hardwired motor, I can use a 40A breaker instead. Does that sound right?
Thanks,
Rick
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Because for NM cable the NEC limits it to the 60 degree C ampacity which means,14 AWG is 15A, 12 AWG is 20A, & 10 AWG is 30A, but w/ THHN conductors, for a motor circuit meeting the requirements of art 430 of the NEC, 14 AWG is 20A,12 AWG is 25A, & 10 AWG is 35A. Please note : These in no way apply to normal branch circuits!!!!
ez-duzit
Well-known member
That sounds plenty good.
So you guys are saying I should take the 50 Amp breaker out and put either a 30 or 40 amp breaker?
Also when you get a new compressor does it come with a wire to hook to the wall?
Can I put a plug on the end or does it need to be hard wired?
How many amps can 12 3 Romex take?
Also when you get a new compressor does it come with a wire to hook to the wall?
Can I put a plug on the end or does it need to be hard wired?
How many amps can 12 3 Romex take?
ez-duzit
Well-known member
Forget 12-3.
The new compressor will probably not have a plug and cable but will surely have a manual explaining the electrical connection.
If your 50 amp circuit was wired correctly, just leave the breaker that's there; it will protect that circuit.
The new compressor will probably not have a plug and cable but will surely have a manual explaining the electrical connection.
If your 50 amp circuit was wired correctly, just leave the breaker that's there; it will protect that circuit.
wyliesdiesels
Well-known member
#12 NM-B(aka brand name Romex) is limited to 20a(60c deg ampacity column) regardless of the number of conductors in the cable. Sorry! 12-3 NM-B is just not gonna cut it for your compressor!
Mr onetwo
Well-known member
The manual for my 1977 IR T30 253 compressor states that for a 5HP motor you are to use #8 THHN or equal up to 100ft.You are to size the breaker at 3 times motor FLA up to a maximum of 70AMP.The FLA of my Baldor motor is 20.6 so I put this circuit on a 60AMP breaker.It has been stated correctly that the sizing for NMB is different.I have a brand new Eaton 30AMP single phase mag starter and the directions that came with it are exactly the same 35 years later.I am not smart enough to contradict these instructions
Spudland_Dave
Well-known member
Good timing...My compressor is not a 7.5hp, For the time being I only have a 3hp...BUT I am about to start wiring it in the next few days. I WAS Gonna use 40A on #8 Romex...BUT now I'm second guessing myself in terms of future proofing.
If NEC Says a 7.5HP is 40A, is the 125% uprating for the purposes of Continuous duty? ie 3hours or more @ 100% utilization?
If NEC Says a 7.5HP is 40A, is the 125% uprating for the purposes of Continuous duty? ie 3hours or more @ 100% utilization?
pattenp
Well-known member
If you think you'll have a comp with a 7.5hp rated motor you should use the 125% and put in a 50A circuit.
greenbluff garage
New member
I just bought the sears 5hp (5.4) 80 gal compressor you were looking at. I used #10 wire and a 30 amp fuse. the compressor is 22 amp. I was told by an electrician that the compressors amps should be 80% of the fuses capacity, so 30 amp is more then enough. If you run your wire longer then 75 feet you will have to up size the wire. 