I am going to wire a 220 v compressor in my detatched garage 60`from the service panel. I tried to test it from an 8000/10000 watt Dewalt generator w/ 30 amp outlet. The compressor has a start and run capacitor w / on / off switch. The compressor will start to run (about 1 sec and trip the 30amp breaker on the Generator. Motor is rated @ 5 hp 18 amp. With the belt off the comp the motor starts and runs immediately. Do I need to use 40 amp breaker for this it seems big for this 60 gal compressor, or is the Generator just not able to run the compressor?
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Wire a 17a 220v compressor
- Thread starter J Tranc
- Start date
pattenp
Well-known member
Generator can't handle the startup load. If motor data label shows 5hp the compressor needs to be hardwired using #10 thhn in conduit or #8 nm. 5hp per the NEC needs 35A rated supply conductors, so use minimum of 40A breaker. You can upsize the breaker to handle startup load provided the motor has its own overload protection.
I question the 5 HP claim. At 18 amps @ 240 volts I would give it 3-1/2 or 4 HP.
There are a lot of 3.7 HP motors out there on compressors that amp out around that 18 amp number.
To the OP the compressor might run the compressor but it is not wired to run that large of load. You can not simply replace the breaker. You need a larger generator and smaller compressor.
There are a lot of 3.7 HP motors out there on compressors that amp out around that 18 amp number.
To the OP the compressor might run the compressor but it is not wired to run that large of load. You can not simply replace the breaker. You need a larger generator and smaller compressor.
wyliesdiesels
Well-known member
18a is smaller than 5hp... gonna be closer to 3.5-4hpI am going to wire a 220 v compressor in my detatched garage 60`from the service panel. I tried to test it from an 8000/10000 watt Dewalt generator w/ 30 amp outlet. The compressor has a start and run capacitor w / on / off switch. The compressor will start to run (about 1 sec and trip the 30amp breaker on the Generator. Motor is rated @ 5 hp 18 amp. With the belt off the comp the motor starts and runs immediately. Do I need to use 40 amp breaker for this it seems big for this 60 gal compressor, or is the Generator just not able to run the compressor?
Having said that, the in-rush current of a motor can be anywhere from 4-8x the FLA. so your genny doesnt have enough surge power to start it...
I sold gerarators for some time. the manufacturers we sold recommended 2-1/2 to 3 times rated amps for motor starting. A 10K generator should start it, 12K would be better, but it isn't his wired for that large of a load.Having said that, the in-rush current of a motor can be anywhere from 4-8x the FLA. so your genny doesnt have enough surge power to start it...
wyliesdiesels
Well-known member
ummI sold gerarators for some time. the manufacturers we sold recommended 2-1/2 to 3 times rated amps for motor starting. A 10K generator should start it, 12K would be better, but it isn't his wired for that large of a load.
18a * 2.5 = 45a
10Kw / 240v = 41.7a
The in-rush current is likely higher than 2.5x FLA so...
He is 800 watts short. It isn't a hard and fast rule, but with an air compressor that pretty much starts under load it might be a bit much. Either way the generator breaker will not handle the load so it doesn't make a difference. A 4 HP motor running a fan I would bet the generator would run it.umm
18a * 2.5 = 45a
10Kw / 240v = 41.7a
The in-rush current is likely higher than 2.5x FLA so...
That will be another can of worms! You will need to over size the wiring for the compressor. Does the motor nameplate show a HP?Thanks every one for your replies. I`ll run a dedicated line to the garage
pattenp
Well-known member
Why do you say he needs to oversize the wire? It needs to be the correct size based on HP if the motor data shows the actual HP.That will be another can of worms! You will need to over size the wiring for the compressor. Does the motor nameplate show a HP?
You don't size the wire by the amp draw, You size it by motor HP. Most guys will go by the amp draw.Why do you say he needs to oversize the wire? It needs to be the correct size based on HP if the motor data shows the actual HP.
pattenp
Well-known member
If you'd said that in the first place I wouldn't have questioned what you were saying. Simply saying that the conductors needed to be oversize wasn't saying why.You don't size the wire by the amp draw, You size it by motor HP. Most guys will go by the amp draw.
nadogail
Well-known member
Generator and small engine power ratings are about as reliable as the “Detroit Horsepower” ratings. IMHO, They should be taken with plenty of Salt.
My little generator was built from an engine rated at 13 horse power and it spins an alternator rated at 10 KW Peak.
I am guessing that the combination is probably good for an honest 6 KW.
My little generator was built from an engine rated at 13 horse power and it spins an alternator rated at 10 KW Peak.
I am guessing that the combination is probably good for an honest 6 KW.
I wasn't going into specifics because I don't know the specifics, just tossing out a warning.If you'd said that in the first place I wouldn't have questioned what you were saying. Simply saying that the conductors needed to be oversize wasn't saying why.
NEC does it that way, yes?You don't size the wire by the amp draw, You size it by motor HP. Most guys will go by the amp draw.
Other Codes size by motor amp rating.
dave*99
Well-known member
Probably about right. Generally takes about 2HP of engine per kW of generator power.Generator and small engine power ratings are about as reliable as the “Detroit Horsepower” ratings. IMHO, They should be taken with plenty of Salt.
My little generator was built from an engine rated at 13 horse power and it spins an alternator rated at 10 KW Peak.
I am guessing that the combination is probably good for an honest 6 KW.