wire size for compressor

[AP514]

I have a 240v 3.7 hp compressor...17.2 rating..but I also will run a 2 amp fan off of 1 of the compressor power legs(pulling off the pressure switch to turn Fan on...getting neutral from near by plug)....

So what size wire do I need and what size CB ??.......compressor says it uses 15a...and to use a 20a breaker.
power run from box is 50 feet total....

Can I use a 12/3 wire and 20 amp double pole CB...or would 10/3 and a 30 amp be better ? or a combo of those ??

 

[GYPSY400]

I would go 10/3 wire and a 20a breaker.. If you ever upsize to a 5hp compressor you will just have to change the breaker to a 30.. Nothing wrong with having the wire larger than needed, as long as it fits into the breaker.


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[600SL]

I think I have the same compressor. I went with 12 ga only because I already had it available plus I'm in conduit so replacing it at a later date is simple. But if I had 10 ga that's what I would have put in.

 

[stage20]

10 all the way. you dont want to burn your compressor up for the small difference in the cost of the wire.

 

[ForceFed70]

There is no way I'd put that on anything less than a 30A circuit. 10ga wire, 30A breaker at a minimum.

 

[pattenp]

Did this compressor come with a cord and plug on it or does need to be hardwired?

 

[600SL]

There is no way I'd put that on anything less than a 30A circuit. 10ga wire, 30A breaker at a minimum.

I can understand the 10ga wire for future upgrades but the 30 amp breaker may be asking for trouble. If this compressor is pulling over 20 amps you would want it to throw the breaker so that you can investigate for a problem.

 

[LS6 Tommy]

Everyone's always asking for breaker & wiring sizes for equipment. I know many of us have "old" equipment and maybe I'm nuts, but assuming you can still get them, wouldn't it just be easiest to follow the manufacturer's electrical requirements?

Tommy

 

[stage20]

Sounds to easy tommy.

 

[AP514]

ok as stated in my OP...........my compressor says to have this....
compressor says it uses 15a...and to use a 20a breaker.

OK no worries But im also adding the 2 amp(starting draw) Fan for my intercooler that will start at the same time the compressor starts http://www.galco.com/techdoc/ebm/w2e250-hj32-01_oi.pdf Page 5

So the Motor say it is 17.2 +2.1 Fan =19.3 amps....Real close to the 20 amp C/B

Now I have 3 wire 12awg (armored cable) already...but im worried C/B and Wire are on the lite side for the draw

 

[pattenp]

If the 19.3A is correct then you are not to put it on a 20A circuit. The circuit needs to be a minimum of 25A. 125% X 19.3 = 24.13A

 

[600SL]

I'm not sure about armored cable but I'm running 12ga THHN in conduit. That's good for 30 amps.

As far as 19 amps on a 20 amp CB I would not do it especially with 2 motors starting at the same time. I have seen 25 amp breakers available.

 

[stage20]

Is the 17.2 the max draw or the running amps?

 

[stage20]

I'm not sure about armored cable but I'm running 12ga THHN in conduit. That's good for 30 amps.

As far as 19 amps on a 20 amp CB I would not do it especially with 2 motors starting at the same time. I have seen 25 amp breakers available.

Its good for a max of 30 amp I wouldn't run it at 30 amps. Jmo

 

[AP514]

Did this compressor come with a cord and plug on it or does need to be hardwired?

No cord. Comp is Husky 60Gal. from HD....going to hard wire (soild) to cut-off box(House and garage are STEEL Frame so MC-Cable is code I think)
I have #12 MC-cable already but not sure if it will be ok ? ?
the Husky Manual says 15a and put on a 20amp C/B..the 17.2 is right from the comp Motor
TOTAL FLA is 19.3-19.6 as close as I can tell... So, I will put in a 25Amp C/B ??

If I buy 10 gauge I will get a 10/4 so I can run a neutral along for the 110v fan. I will go Stranded wire from Cut-off box to compressor. I am looking at $100 for 50 Ft.

 

[600SL]

Its good for a max of 30 amp I wouldn't run it at 30 amps. Jmo

Neither would I but 20 would be fine. Just not sure if the 12 ga armored cable has the same rating.

 

[May Pop]

PattenP is the closest to being correct over anyone. For a machine the largest motor is multiplied by 1.25%. so 17.2 x 1.25 = 21.5 Add the 2.1 either way and your over the 16 amps which is all a 20 amp circuit is to be loaded to (80%). This takes you to 25 being the next size available of fusing. 25 Amp breakers are available but not always common. So a 30 is acceptable by most inspectors. Next is the wire. Some areas allow #12 for 25 amps. At 50 feet you are nearing the point of raising a size due to voltage drop so using 10 gauge is a common sense approach.

 

[Norcal]

PattenP is the closest to being correct over anyone. For a machine the largest motor is multiplied by 1.25%. so 17.2 x 1.25 = 21.5 Add the 2.1 either way and your over the 16 amps which is all a 20 amp circuit is to be loaded to (80%). This takes you to 25 being the next size available of fusing. 25 Amp breakers are available but not always common. So a 30 is acceptable by most inspectors. Next is the wire. Some areas allow #12 for 25 amps. At 50 feet you are nearing the point of raising a size due to voltage drop so using 10 gauge is a common sense approach.

The allowances for 12 AWG to be rated at 25A does not apply where NM cable is used under any circumstances.

 

[May Pop]

Where Im at #12 is 20Amps max. Never more.

 

[pattenp]

AP514, If you are hardwiring it with NM-b (Romex), use 10-3 (to get your neutral, ground is not counted in the number) and put it on a 30A breaker. The overcurrent protection is for the circuit, not the compressor. Even though the instructions say to put it on a 20A circuit that is the minimum circuit size and has nothing to do with protection of the compressor motor. The motor should have its own overload protection built-in.

 

[AP514]

Is the 17.2 the max draw or the running amps?

17.2 is FLA off of motor.....Nec chart has 3 HP as 17..but mine is a 3.7 HP so I guess the extra FLA of .2 So to get the C/B you take the FLA X 1.25% this takes me to the 24. .....just under the 25 amp C/B I am looking at getting.

As I will be pulling off 1 of the 230v legs after/at the Pressure switch to get my 110v for the fan I think I will put in a 4 amp inline fuse.


So, what I have so far from advice here....Still not clear on #2-3
1) Use MC-10/3 wire for my Run to Cut-off box..
2) Still not clear on the C/B but you guys think 25Amp will do better than the lager 30Amp for protection. I just do not want the C/B to be overkill and never trip if there is trouble.
3) Put inline fuse 3-4Amp for Fan motor protection. 4amp is double the draw at start maybe 3 would be better ?

 

[pattenp]

If you use #10 wire then a 30A breaker is fine. If you want to use a 25A breaker that's fine too. You may end up paying more for a 25A breaker than a 30A breaker. The breaker protects only the #10 circuit. If you want to put a small fuse on the fan circuit then by all means do so.

 

[AP514]

Well, got the 25 AMP C/B....it was 2 bucks more than the 30.

Looked all over for 60 ft of 10/3 Solid MC..they all wanted me to buy a 125 ft or 250 ft Spools. finally got Elliot Electric to sell me 60 ft
Now if I could just find some one to sell me 10 feet of Stranded 10/3 MC.

Guess they can't make money selling to the little guy

 

[Mustang51js]

Any Home Depots in the area

 

[alfredeneuman]

Stranded #10 MC is a pretty tall order. I don't imagine any of the wholesale houses stock it.

How about using stranded #10 in Flex Conduit? It's readily available at the Big Box Stores.

 

[stage20]

Stranded #10 MC is a pretty tall order. I don't imagine any of the wholesale houses stock it.

How about using stranded #10 in Flex Conduit? It's readily available at the Big Box Stores.

all i have seen is 6ft "whip it" kits with fittings and wire. i used it on my disconnect on my compressor and also from the electric motor to the pressure switch when i rewired it. 10 bucks for the kit if the length will suit you. stranded thhn in the kit.

 

[Forest Road]

I'm onboard with going 10/3 for your power source. Trying to save $5 on any electrical project is a recipe for disaster.

Also how far is the compressor from the panel? For a dedicated ckt anything over 85' we always upgraded to the next wire size. Although voltage loss over this length is minimal it will affect the breakers capacity. And no matter what wire size is used the breaker dictates max load. What are you going to do if the load trips out a 20a brk with your 12g wire? At least w 10g you can step il to a 25a brk.

 

[AP514]

Yes, using a 25A breaker and 60ft of MC-10/3 solid to my cut-off box..found some 3/8 Flex conduit at HD....Also Bought 4 wires of 10 gauge stranded there. I will pull it into the 3/8 flex. also got the 3A in line fuse for the Fan...all is ready to wire will keep you all posted...

 

[sberry]

I havnt ever used a 25A breaker.

 

[TractorJeff]

Along the same line as original post.
My neighbor has a BRAND NEW 80 gallon ("7hp") Sanborn Compressor sitting in his shop.
Motor is labeled 208-240V, HP "SPL", 17amps(?).
It has cord to plug in an outlet, cord going down to the pressure switch.
Both these cords go under a plastic black cover on the tank/motor mount.
Made me think of this thread when I saw it.

 

[C96]

Along the same line as original post.
My neighbor has a BRAND NEW 80 gallon ("7hp") Sanborn Compressor sitting in his shop.
Motor is labeled 208-240V, HP "SPL", 17amps(?).
It has cord to plug in an outlet, cord going down to the pressure switch.
Both these cords go under a plastic black cover on the tank/motor mount.
Made me think of this thread when I saw it.

Lol, 7hp my a-hole. More like 3hp tops. Just another Bull Sh-t compressor company trying to F-ck the general public.

Something really needs to be done about these BS fake horsepower ratings.

Here’s to you Sanborn and all your deceiving "peak" horsepower rated cheese ball compressors

 

[PRH44]

Along the same line as original post.
My neighbor has a BRAND NEW 80 gallon ("7hp") Sanborn Compressor sitting in his shop.
Motor is labeled 208-240V, HP "SPL", 17amps(?).
.

SPL stands for "Special". This means the compressor manufacturer has requested a different set of specifications and therefore it must be made special for that application. With SPL listed on the motor data plate, it means all bets are off. The HP listed can be anything that motor can produce at peak output before failure. So they can list it virtually anyway they want. Keep in the following terms are used to justify such ratings.
SPL
Peak HP
Developed HP
Rated HP
Max HP



Always look at the full load amps on these SPL motors and compare to NEC Table 430.248 or reputable motor manufacture table. This will give the more true HP rating

 

[AP514]

I havnt ever used a 25A breaker.

I will let you know how it turns out