z28toz06
Well-known member
I am doing my wiring now and I am locating my compressor about 50 feet from the panel. it will be a 220 volt 5 horsepower unit (don't know which one yet) is 10-3 wire big enough?
Wire size for Compressor
- Thread starter z28toz06
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timgr
Well-known member
My heaters are each on a 30A circuit and use 10-2 wiring. No harm in using larger wire though.
What's the size of the breaker? You don't want the wire to melt before the breaker trips. A 50A 220/110 stove/cooktop is supposed to use 6 ga IIRC.
What's the size of the breaker? You don't want the wire to melt before the breaker trips. A 50A 220/110 stove/cooktop is supposed to use 6 ga IIRC.
Charles (in GA)
Well-known member
The catch here is the "about 50 ft" from the panel. If the compressor is more than 50 ft from the panel, or is NOT in line of sight of the panel, no matter how far, you must have a disconnect at the compressor itself. This can be something as simple as a pullout type of device like you would use on an outside A/C unit, or something such as a small subpanel with a breaker in it for the compressor. Be sure and include the up and down distance in your measurements, 50 linear feet could easily turn into 70 ft or more of wire.
Wire size vs amp capacity in part depends on the type of insulation on the wire, thus the ratings of the wire, such as THHN, TW, etc.
A true 5 hp compressor should draw somewhere around 28 amps. Especially since you don't have the compressor yet, you would be wise to go large on the wire, at least #8, and if there is any chance at all that you might end up with a 7.5 hp compressor, go with #6. If you elect to install a subpanel at the compressor (other circuits in this area could be handy) you also would need to carry a neutral to the subpanel.
Money "wasted" right now will be money "well spent" later on when you need the larger circuit or extra capacity.
Charles
Wire size vs amp capacity in part depends on the type of insulation on the wire, thus the ratings of the wire, such as THHN, TW, etc.
A true 5 hp compressor should draw somewhere around 28 amps. Especially since you don't have the compressor yet, you would be wise to go large on the wire, at least #8, and if there is any chance at all that you might end up with a 7.5 hp compressor, go with #6. If you elect to install a subpanel at the compressor (other circuits in this area could be handy) you also would need to carry a neutral to the subpanel.
Money "wasted" right now will be money "well spent" later on when you need the larger circuit or extra capacity.
Charles
NEC 430.22(A)
Branch circuit conductors suppling a single motor used in a continuous duty application shall have an ampacity of not less than 125 % of the motors full-load current rating.
note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use.
A compressor would come under Periodic duty as defined by the NEC but if your motor is rated as continuous duty you would increase wire size to 140% according to table 430.22(E)" Duty -Cycle Service"
I would consider the compressor continuous duty and disregard table 430.22(E)
1.25X 28= 35amps next wire size #8cu.good for 50 amps (only TW and UF types are rated under)
A 7.5 hp motor draws 40amps at 230v. 40X1.25=50amps code legal, but a minimum.
The "50' and within site rule" is line of site, not wire as measured, this is for safety reasons, so if you are working on the motor you can see the disconnect. People do start motors without looking. A cord and plug is considered a disconnect.
Hope this helps
Mark
Branch circuit conductors suppling a single motor used in a continuous duty application shall have an ampacity of not less than 125 % of the motors full-load current rating.
note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use.
A compressor would come under Periodic duty as defined by the NEC but if your motor is rated as continuous duty you would increase wire size to 140% according to table 430.22(E)" Duty -Cycle Service"
I would consider the compressor continuous duty and disregard table 430.22(E)
1.25X 28= 35amps next wire size #8cu.good for 50 amps (only TW and UF types are rated under)
A 7.5 hp motor draws 40amps at 230v. 40X1.25=50amps code legal, but a minimum.
The "50' and within site rule" is line of site, not wire as measured, this is for safety reasons, so if you are working on the motor you can see the disconnect. People do start motors without looking. A cord and plug is considered a disconnect.
Hope this helps
Mark
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So what about the start up draw ? I know we have been through this many times but ,
Not sure on the 28 amp 5 hp motor but my 7.5hp motor is at 33 running amp and the start up draw is around 76 amps ! Thus the reason i installed a #4 wire on mine and an 80 amp breaker.
I would think for the 5hp unit i would run at least # 6-2 wire and a 60 amp breaker. The compressor will work on less but we know what happens with lack of wire on electric motors ..............
Not sure on the 28 amp 5 hp motor but my 7.5hp motor is at 33 running amp and the start up draw is around 76 amps ! Thus the reason i installed a #4 wire on mine and an 80 amp breaker.
I would think for the 5hp unit i would run at least # 6-2 wire and a 60 amp breaker. The compressor will work on less but we know what happens with lack of wire on electric motors ..............
Well the instruction manual or the manufacturer will tell you the breaker size to use, then just use the correct wire size as above. Unless you are going quite a distance, mine was way under 50ft so I never worried about long length. Going larger will not hurt anything, only alot more expensive especially price of copper now, and stiff as @#*@( to run...
So what about the start up draw ? I know we have been through this many times but ,
Not sure on the 28 amp 5 hp motor but my 7.5hp motor is at 33 running amp and the start up draw is around 76 amps ! Thus the reason i installed a #4 wire on mine and an 80 amp breaker.
I would think for the 5hp unit i would run at least # 6-2 wire and a 60 amp breaker. The compressor will work on less but we know what happens with lack of wire on electric motors ..............
You should be able to up the breaker size WITHOUT upping the wire size if in fact you are having nuisance tripping. You shouldn't need #6 for a 5hp unit unless the motor is far away from the panel.
With a 76 amp start up draw I'll stick with #4 wire vs anything that could be undersized.
This is also what Ingersoll Rand and a local electrictan told me when i confirmed the question with them before i installed the compressor.
It comes down to an extra $13. to do it how i felt was the RIGHT WAY.
BTW ,
I wouldnt put an oversized breaker on an undersized wire, Dont think thats a good idea.
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It's allowed, by code, for certain things like a compressor on a dedicated circuit.
I'll second that. It could be handy if you are using a magnetic starter with a 120V coil, too.
All i know is what info i came up with and what IR and a pro installer told me on my compressor so i cant say for sure.
I guess my question to you would be why ? I guess i could of saved $5.oo by going that route by why would one fight to go smaller to save just a few little $$.
( maybe fight is not the correct term
) The start-up spike doesn't last long enough to over heat the wire, thats why you don't have to size the wire for the spike.
The code does allow for a larger size breaker:
Table 430.52
Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Devices
Single-phase motors- "Inverse Time Breaker" 250% of full load current
28amps X 2.5= 70 amp breaker maximum
Mark
The code does allow for a larger size breaker:
Table 430.52
Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Devices
Single-phase motors- "Inverse Time Breaker" 250% of full load current
28amps X 2.5= 70 amp breaker maximum
Mark
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What he said.
Remember, the breakers and the wire is not going to go up in smoke if you go over the normal specs for a short period of time. There is a lot of safety built into the components.
Maybe if the run of wire was very short, would the price differential be neglible. All I know is with the price of copper and the lengths I would need, bumping up to the next size wire wouldn't be worth it.
Maybe if someone has the code listing for the amount of A a wire can take for a short period of time...I know I've seen the chart before. Might make it a little easier to see/understand.
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So with what katmat & markb1 posted that would give me an 80 amp breaker with #4 wire has i have installed with my 7.5hp compressor, so that shoud put a 5hp compressor at a #6 wire with a 70 amp breaker.
The NEC is complicated and confusing to say the least. It can be interpertated in different ways and challenged. I'll try to outline the motor circuit calculation.
Step 1 full load current
NEC 430.22(A)
Branch circuit conductors suppling a single motor used in a continuous duty application shall have an ampacity of not less than 125 % of the motors full-load current rating.
5 hp 230v motor 28a X 1.25= 35amps
Step 2 wire size from calculated amperage
NEC Table 310.16 Allowable Ampacities of Insulated Conductors Not more than 3 current carrying conductors in Raceway, cable or earth directly buried
From table: #10 cu 30amps, #8 cu. 50amps use #8 cu.
Step 3 select breaker size:
Table 430.52
Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Devices
Single-phase motors- "Inverse Time Breaker" 250% of full load current
28amps X 2.5= 70 amp breaker maximum.
note maximum, if a 40amp breaker will work without tripping on start up use it.
Hope this makes things a little more clear.
Mark
Step 1 full load current
NEC 430.22(A)
Branch circuit conductors suppling a single motor used in a continuous duty application shall have an ampacity of not less than 125 % of the motors full-load current rating.
5 hp 230v motor 28a X 1.25= 35amps
Step 2 wire size from calculated amperage
NEC Table 310.16 Allowable Ampacities of Insulated Conductors Not more than 3 current carrying conductors in Raceway, cable or earth directly buried
From table: #10 cu 30amps, #8 cu. 50amps use #8 cu.
Step 3 select breaker size:
Table 430.52
Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Devices
Single-phase motors- "Inverse Time Breaker" 250% of full load current
28amps X 2.5= 70 amp breaker maximum.
note maximum, if a 40amp breaker will work without tripping on start up use it.
Hope this makes things a little more clear.
Mark