7.5 HP Compressor Wiring & Future Garage Wire Size

[cloves]

Hi all,

I just picked up a NorthStar Electric Air Compressor 7.5 HP (2 Stage - 1 Phase) after almost a year of sitting on the fence. After reading on the forums here I will using 6/3 wire with a 50 amp breaker (compressor is about 65 ft away from the box).

I am in the middle of construction and have my walls open so I wanted to run my wiring for the "future garage" now, which will be next to my current garage. Since the compressor needs its own 6/3 circuit, what should I do about providing power to the rest of my garage? I was thinking of running another 6/3 wire to a subpanel in the garage. I have wood working tools and a 220v welder currently. Eventually might even get a lift when money allows. The garage isn't even built yet, but I would like to have all my wiring already in my walls before I close up my walls.

 

[mike93lx]

You don't need 6/3. Just two hots and a ground, so 6/2.

You can't run two feeds to an outbuilding. Run larger wire and a subpanel. 2-2-2-4 MHF is a common recommendation here, giving you 90a. If the new garage will be attached, then you can run multiple lines. I would still do a single subpanel and tie the comp to that if possible

 

[wyliesdiesels]

Is this garage attached or detached?

If detached, you can only run one feed to it and NM-b cannot be used outside or underground so you will need to use another wiring method.

 

[cloves]

Garage is attached (Sorry forgot to mention), does that change what feeds I can run?

@mike93lx thanks for that tidbit, I must have misread the previous threads I found. Thought for sure it was 6/3 wire. 2-2-2-4 MHF gives me 90 so that means I would be able to just run 2-2-2-4 MHF and then add a 60 amp breaker for the compressor at the subpanel in the garage right?

 

[mike93lx]

If attached, don't use MHF. Use SER if you can do so in a way that keeps it protected from damage.

Yes, add a sub and then comp from that

 

[wyliesdiesels]

Yeah dont bother with MHF for an attached garage.

You would have to install conduit.

SER would be much easier.

And ditch the homerun of 6/2 NM-b for the compressor.

Just install a subpanel fed with #2 SER and then run the compressor circuit off the subpane.

Make sure to isolate the neutral busses in the subpanel.

 

[nadogail]

Enjoy the compressor.

 

[sberry]

The 2 alum makes for an ideal feed to a garage. Put a panel with more spaces so adding additional circuits is a local matter.

 

[mike93lx]

Curious, did you confirm that 7.5hp is ok with your Poco? That's past what some set as a limit

 

[cloves]

Thanks for all the info guys, wish I asked before I went out and got some cable like a dope. I picked up 2 reels of 6/3 wire in cash so I guess I will have to put that up for sale.

Since the garage isn't built (probably a year out) would I be able to roll up an extra 10-15ft of the in the stud bay of the 2-2-2-4 G (Or hang from the wall)? I need to use the compressor for some work since its already in the garage.

@mike93lx, I didn't even know I would have to call the poco for this since its single phase. I have 200 amp service coming into the house.

So as of right now I need to pick up a small sub panel and "2-2-2-4 Gray Stranded AL SER Cable". Also need a 50 or 60 amp breaker for the small sub panel. Any recommendations on size for the sub panel and will I also need a cut off switch with a small panel in the garage? I still have an old subpanel from when the house was 100 amp service, maybe I can recycle that for the sub?

Few photos below, electrical motor is a Baldor.

[/ATTACH]

 

[wyliesdiesels]

yeah some PoCos have limits on motor HP.

#2 Al is good for 90a

If you want top of the line go with an Eaton CH

The motor label pic you posted doesnt tell us anything about the motor other than rotation connections.

 

[cloves]

thanks wyliesdiesels, the old panel I have is an Eaton . My new main panel is also an Eaton BR. I am hoping I can use the older panel in the garage for now. Think the main breaker on this one is missing from what I am seeing (old panel photos attached).

Here is the motor label, its on the motor side so it was a bit tricky to shoot.

So basically I would eventually have 90 amps going into the garage and my compressor would pull between 40-50 when running leaving about another 40/50 amps for other tools etc if they are running at the same time (low chance of that)

 

[Bert_]

The old panel is a Eaton CH or Cutler Hammer. It's a way better panel than the Eaton BR.

The motor pulls 29 amps at full load. It's's not a question, it says right on the tag.

 

[Norcal]

The old panel is a Eaton CH or Cutler Hammer. It's a way better panel than the Eaton BR.

The motor pulls 29 amps at full load. It's's not a question, it says right on the tag.

The CH is the best, the BR is the worst which is one of the reasons I call the BR panels “Zinsco II”. Every other make is in between.

 

[wyliesdiesels]

thanks wyliesdiesels, the old panel I have is an Eaton . My new main panel is also an Eaton BR. I am hoping I can use the older panel in the garage for now. Think the main breaker on this one is missing from what I am seeing (old panel photos attached).

Here is the motor label, its on the motor side so it was a bit tricky to shoot.

So basically I would eventually have 90 amps going into the garage and my compressor would pull between 40-50 when running leaving about another 40/50 amps for other tools etc if they are running at the same time (low chance of that)

where did you get 40-50a?

 

[cloves]

where did you get 40-50a?

Running the motor should pull 29-32 amps, but from what my old man mentioned the motor draws a lot more when it starts up then when running. The instructions for the compressor say to use a 40 amp circuit and the the northern tool web site says a 50 amp circuit (assume so I get no trips). I was guessing too high on the initial draw of the motor I assume?

https://www.northerntool.com/shop/tools/product_200596487_200596487

 

[wyliesdiesels]

Running the motor should pull 29-32 amps, but from what my old man mentioned the motor draws a lot more when it starts up then when running. The instructions for the compressor say to use a 40 amp circuit and the the northern tool web site says a 50 amp circuit (assume so I get no trips). I was guessing too high on the initial draw of the motor I assume?

https://www.northerntool.com/shop/tools/product_200596487_200596487

you are mixing things up here.

your previous comment said 40-50a WHEN RUNNING. Running amps and startup amps are 2 different things. thats why i posted my previous comment. You were doing a WAG for the load on the feeder based on the startup amps which is not the way to go about a load calc.

Startup amps are only for fractions of a second (200ms approx) and are not what is used for a load calc nor for sizing the motor circuit.

The instructions are a bit vague if they say to use a 40a circuit. While a 40a breaker may hold with the startup current and be ok, the wire for motor circuits needs to be sized @ 125% of the NEC FLC listed in table 430.248. For 7.5HP this is 40a. So this equates to 50a rated wire- #6/2 NM-b or #8 in conduit.

now back to the breaker. you can size it upto 250% of the FLC. This equates to 100a breaker. Doubt youll need that high of a breaker. 40a may be fine or you may need 50a due to nuisance trips.

 

[sberry]

Yes it takes more when it starts but also the fact that it is sized up is what protects the wire from thermal overload.
The load could be continuous too.

 

[Bert_]

You don't figure anything by the start-up amps. Start up on a 7.5 hp motor will probably be 150 amps.

 

[sberry]

Yes but good heavy wire does make for good starts. Its a motor start, its gonna V drop, if it didnt it wouldnt move,,, ha But some dont hurt much.

 

[wyliesdiesels]

Yes but good heavy wire does make for good starts. Its a motor start, its gonna V drop, if it didnt it wouldnt move,,, ha But some dont hurt much.

not for capacitor started motors.

 

[sberry]

Yes, it was kind of a basic concept.

 

[cloves]

Hi all, trying to figure out how to get the 2-2-2-4 SER AL cable to the garage. Since we are adding a second floor soon running it in the attic isn't going to work (Floor joists and roof coming off soon). I was thinking of running some pvc conduit (2" or 1-1/4") outside for about 35 ft and then turning into the garage under the eave. That would mean a 90 degree bend for the SER cable which I am not sure is too hard of angle.

Originally I was going to run the cable in the attic and hook into the subpanel in the garage but with the roof and floor joist about to come off that wouldn't work. Should I instead use individual conductors instead (#2, #2, #2, #4 bare?) which I would assume require some sort of conduit inside as well. Part of the run is in the basement before it hits the outside Still want to be able to use the cable for the newer attached garage down the road.

 

[u3b3rg33k]

You don't figure anything by the start-up amps. Start up on a 7.5 hp motor will probably be 150 amps.

a similar 5hp is around 122 LRA.

 

[cloves]

Hi fella's just reading up on code and wanmy panel. Apparently, as of NEC 2008, I can only run 90amps in the sub panel so in my main panel I am going to add a 90 amp 2 pole breaker to feed the subpanel.

I will be reusing the old Eaton CH which is a "main lug style". I will connect the compressor to a 50 amp breaker. I need to make sure to isolate the neutral bus on the subpanel by removing the connector to the can as @wyliesdiesels mentioned. This panel doesn't have a grounding bus so I will need to add one as well. Believe that should screw into the panel and I believe I also have to add two grounding rods outside.

So far we have run about half the 2-2-2-4 cable in 2 inch pvc conduit. I have 2-90 degree service entry boxes and its been hell bending the cable and running it, and yes we have been using the lube and we aren't weaklings . I decided not to glue the connections until I get all the cable run. Any tips on the bending?

Any other details I might have missed?

 

[mike93lx]

Wow. Lots of stuff wrong there. You need to glue up the conduit first. No gluing as you go.

What cable are you running? Hopefully not SER.

You can't use a main lug panel without a means of disconect, assuming this is detached and no within line of sight of the main.

Start your own thread and list this stuff out.

 

[cloves]

Hi Mike, this was my thread.

• Garage is attached.
• Running SER 2-2-2-4 in 2" PVC conduit (two 90 sweep turns and two service entries) since we ran it on the outside of the house for now. This will only be temporary until construction is complete. Once I am done I will be running the SER cable in the studs to the new attached garage right next to the current garage. I left an extra 10ft on wound around and attached to the wall and hung for now.
• Attached garage is about 80ft from the main panel do I still need a disconnect in the garage? What would be the best to accomplish this? I was hoping to reuse to old eaton CH lug panel I had lying around.

 

[wyliesdiesels]

Hi fella's just reading up on code and wanmy panel. Apparently, as of NEC 2008, I can only run 90amps in the sub panel so in my main panel I am going to add a 90 amp 2 pole breaker to feed the subpanel.

I will be reusing the old Eaton CH which is a "main lug style". I will connect the compressor to a 50 amp breaker. I need to make sure to isolate the neutral bus on the subpanel by removing the connector to the can as @wyliesdiesels mentioned. This panel doesn't have a grounding bus so I will need to add one as well. Believe that should screw into the panel and I believe I also have to add two grounding rods outside.

So far we have run about half the 2-2-2-4 cable in 2 inch pvc conduit. I have 2-90 degree service entry boxes and its been hell bending the cable and running it, and yes we have been using the lube and we aren't weaklings . I decided not to glue the connections until I get all the cable run. Any tips on the bending?

Any other details I might have missed?

what code is saying this?

Without a load calc, you couldnt possibly come up with this.

Wow. Lots of stuff wrong there. You need to glue up the conduit first. No gluing as you go.

What cable are you running? Hopefully not SER.

You can't use a main lug panel without a means of disconnect, assuming this is detached and no within line of sight of the main.

Start your own thread and list this stuff out.

actually one CAN USE a main lug panel in a detached as long as there is 6 or less breaker handles

 

[mike93lx]

Hi Mike, this was my thread.

• Garage is attached.
• Running SER 2-2-2-4 in 2" PVC conduit (two 90 sweep turns and two service entries) since we ran it on the outside of the house for now. This will only be temporary until construction is complete. Once I am done I will be running the SER cable in the studs to the new attached garage right next to the current garage. I left an extra 10ft on wound around and attached to the wall and hung for now.
• Attached garage is about 80ft from the main panel do I still need a disconnect in the garage? What would be the best to accomplish this? I was hoping to reuse to old eaton CH lug panel I had lying around.

My bad, reading it, it felt like someone else.

Yes, you need a disconnect if using more than 6 breaker handles, as noted by Wylie. I would buy a new panel before using a separate disconnect with an old panel. They just aren't expensive enough to justify all that

what code is saying this?

Without a load calc, you couldnt possibly come up with this.



actually one CAN USE a main lug panel in a detached as long as there is 6 or less breaker handles

Thanks for the clarification. I was thinking in the context of a larger panel, but should have mentioned that.

 

[cloves]

what code is saying this?

Came across this in the forums: (link) "2224 ser isn't legal for 100 amp subpanel if on 2008 code or newer. Its only good for 75 amps"

So just to recap:
- Ran 2-2-2-4 SER cable to the attached garage (total run was 110ft of cable, left the extra cable rolled up against the wall and secured)

- Wanted to use the old Eaton CH lug style panel I have since it had a copper bus but looking over at prices, mike93lx seems correct they are pretty cheap and would have a disconnect.

Questions:
- Since I ran 2-2-2-4 SER, I should be able to run a 90amp 2-pole breaker from my main to feed my sub panel, unless of course that 2008 code snippet from above is correct.

- What is the max amp sub panel I can install? (90amp or 75amp)?

Thanks to all who have shared their wisdom so far!

 

[mike93lx]

AFAIK, 90a breaker is fine with 2224 ser.

Regardless, you can put any size panel you want in the shop. 90,100,125,200, doesn't matter. The breaker feeding it in the house can't be bigger than 90, but the breaker in the sub is just a means of disconnect. I would strongly recommend putting a large panel in your shop, probably something with a 200a main and a lot of spaces.

 

[cloves]

Thanks mike93lx,

So I will be picking up a 90amp 2-pole breaker for the main panel to feed my sub panel.

Why do you recommend a 200 amp panel for the garage out of curiosity? Is it just so I have more spaces available? Fulling knowing that I can't run tthat much power at the same time?

 

[mike93lx]

Thanks mike93lx,

So I will be picking up a 90amp 2-pole breaker for the main panel to feed my sub panel.

Why do you recommend a 200 amp panel for the garage out of curiosity? Is it just so I have more spaces available? Fulling knowing that I can't run tthat much power at the same time?

Space is it. More room for wire, more room for breakers. What you can consume doesn't matter.

 

[sberry]

They make 100/24 space, 20 is really common. A few extra spaces when you are done is good, so easy to hook up new equipment.

 

[cloves]

So we are just about ready to wire up the compressor.

My 2-2-2-4 wire isn't "southwire", its some other brand from the electric supply in our area. Color of the wires are black-red stripe, black-white stripe, black, and of course bare ground. What should I use as my two hot wires black-red stripe, black-white stripe and the solid black as my neutral?

My old man also mentioned that we had the potential of wiring the motor backwards which he said could be bad for the motor. Is it possible to wire the incorrect polarity based on which leg goes to and from the main panel?

 

[Norcal]

So we are just about ready to wire up the compressor.

My 2-2-2-4 wire isn't "southwire", its some other brand from the electric supply in our area. Color of the wires are black-red stripe, black-white stripe, black, and of course bare ground. What should I use as my two hot wires black-red stripe, black-white stripe and the solid black as my neutral?

My old man also mentioned that we had the potential of wiring the motor backwards which he said could be bad for the motor. Is it possible to wire the incorrect polarity based on which leg goes to and from the main panel?

I doubt a OEM compressor motor is reversible, no need, & extra cost on a competitive product, and reversing the single phase leads will not reverse the motor, if it was 3 phase then would have to be mindful of rotation.

 

[Bert_]

So we are just about ready to wire up the compressor.

My 2-2-2-4 wire isn't "southwire", its some other brand from the electric supply in our area. Color of the wires are black-red stripe, black-white stripe, black, and of course bare ground. What should I use as my two hot wires black-red stripe, black-white stripe and the solid black as my neutral?

My old man also mentioned that we had the potential of wiring the motor backwards which he said could be bad for the motor. Is it possible to wire the incorrect polarity based on which leg goes to and from the main panel?

Black and black/red are hot. The one with white stripe is neutral.

 

[cloves]

Guys thanks for the help, finally got the compressor up and running. Now I can finish off this car I am working on that I need to sell for some cash. Thanks for all the help!

 

[mike93lx]

Nice, glad to hear