Air Compressor Wiring

[PE 316]

I know, I know, here is ANOTHER thread about air compressor wiring...

However, I have done alot of thread searching of this topic over the last several weeks and still have a few questions.

It's time to wire-up my new (to me) Quincy air compressor.

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Here are the COMPRESSOR specs:
.

• Manufacturer: Quincy
  
• Model: QTS-5
  
• Horsepower: 5 HP (Single-Stage)
  
• Tank Capacity: 60 Gallon
  
• Compressor RPM: 900 RPM
  
• CFM: 18.0 @ 90 PSI 21.0 @ 40 PSI)
  
• Maximum Pressure: 125 PSI
  
• Lubrication: Splash
  .
  
  
• Electric Motor: Baldor
  
• Cat. No: 1274661009
  
• Spec: 19E010W026
  
• HP: SPL
  
• Voltage: 230 (Single-Phase)
  
• Amps: 21 Amps
  
• Motor RPM: 3,450 RPM

.

I need to run a new 240V line from my from my electrical service panel (meter) to the location of my air compressor.
The distance I need to run is < 40' cable run. I already have 40' of 8/3 NM-B wire.

I also plan to add a 50 AMP outlet for a MIG welder in the general location of the air compressor as well

Here are the MIG Welder specs:
.

• Manufacturer: Lincoln Electric
  
• Model: Weld Pak 180HD
  
• Voltage: 230 V (60 Hz)
  
• Input Current: 20 AMPS (@ rated output)
  
• Recommended Fuse/Breaker: 40 AMP Super Lag
  
• Input Amps: 20 AMPS

.
Here are my questions:

1. What Breaker Box should I buy?
   
2. What AMP rating?
   
3. Which type breaker(s) will I need?
   
4. Can a Safety Disconnect Switch be used as a Breaker Box?

 

[pattenp]

You need to clear something up about what you want to do. Are you wanting to put in a sub-panel with breakers for the mig and comp? Why do you have 8/3 NM? The mig and comp only need 2 hots and a ground, such as 8/2 NM. 8/3 NM is 2 hots, 1 neutral and a ground.

 

[PE 316]

I was given the 8/3 wire. Will this cause a problem? Should I replace with 8/2 wire to stay within code?
.
Yes, I was thinking of adding a sub panel and possibly a Safety Disconnect Switch for the compressor...

 

[sberry]

If you can see the panel, this is in a small garage keep it simple, the 8 is fine and would use a plug as a disconnect. Use a 30 or 40 for that, either one is fine, I have one on a 30 never tripped it.

As for the welder, the people that wrote the specs for that model in the manual were sniffing the circuit board glue, its been that way for a long time and have not seen something quite like that in any other manual. Run a 12 or better, I like a 10 for these it gives these small machines all the help they can get,,, and use a 30-50A breaker, a 10 wire 30 breaker is s tailor made circuit for them. You can plug a 50A stick machine to this if you use a 50, its the only advantage of a breaker that high.

Don't let anyone BS you about that machine,, its a box store model etc. It is a good unit

 

[pattenp]

I’ll assume your garage/shop is attached to the house. The mig and comp can be single 240V circuits from the main panel if you don’t need any additional 120V circuits in the garage. If you do need additional 120V circuits then adding a sub-panel will be the best method. If just doing the two 240V circuits I’d use the 8/3 for the mig running it off a 40A breaker with a 50amp 6-50R outlet and wirenut off the white neutral for future use if needed. Then I’d run 10/2 off of a 30A breaker to a 60A A/C disconnect box and hardwire the Comp to the disconnect with flex conduit using #10 THHN wire. If you do the sub-panel I’d do a 60A at a minimum using #6 copper and then do the same two 240V circuits from the sub. If either the sub-panel or the main panel is in sight of the Comp then the disconnect box is not needed because the breaker in the panel can be considered as the disconnect.

Use this for disconnect ... http://www.homedepot.com/h_d1/N-5yc...rd=a/c+dissconnect&storeId=10051#.URZX0B1EFpE

Use this for Sub-panel ..... http://www.homedepot.com/h_d1/N-5yc...d=main+load+center&storeId=10051#.URZYXh1EFpE

or this with no main breaker... http://www.homedepot.com/h_d1/N-5yc...1&keyword=main+lug&storeId=10051#.URZZNB1EFpE

 

[PT Doc]

Leviton makes a 5hp 240v 50 switch. Much smaller than the ac disconnects.

 

[Norcal]

Leviton makes a 5hp 240v 50 switch. Much smaller than the ac disconnects.

You cannot beat the price for a pull out type A/C disco, in most cases less then $10.

 

[Flash69]

I just did this exact thing for my compressor 2 weeks ago.

I cut my wall open (approx. 4 inches by 18 feet) and ran 8-2 NM-B in the wall studs. I used a 40 amp double pole breaker and the same Square D disconnect pattenp linked to above.

While I already had the wall open I added 3 more 120v outlets spaced out along the wall. These were connected to a previously added GFCI circuit on a 20 amp breaker. I used 12-2 for the 120v outlets.

 

[PT Doc]

You cannot beat the price for a pull out type A/C disco, in most cases less then $10.

My was 35 off amazon. Fits in a 2gang handy bo, very clean install but yes a few more bucks.

Are these ac switches rated to cut power to a 5 hp motor?

 

[pattenp]

My was 35 off amazon. Fits in a 2gang handy bo, very clean install but yes a few more bucks.

Are these ac switches rated to cut power to a 5 hp motor?

The A/C disconnect is to be used as a power disconnect, not as a motor on/off switch.

 

[PE 316]

Guys, THANKS for all your input and tips!

I will be tapping into to the 30 Amp breaker on the household meter box for my supply:

I will replace the dual 30A breaker with a 30A/40A dual quad breaker assembly like this one:

(Note: I mistakenly picked-up a 30A/50A Quad Breaker - I hope they'll let me exchange it)


Here is what I ended up doing:

I ran a 40A / 240V leg for the air compressor feed and the MIG welder outlet. (compressor & MIG welder will not be operating at the same)





I utilized the 8/3 wire to split a 120v leg and added a 20A GFCI outlet for my Auto-Drain

 

[pattenp]

A 20A outlet on a 40A circuit is a NEC violation.

 

[PE 316]

Recommendation to correct?

 

[pattenp]

If the Auto Drain is a 120V plug in device then it needs to be plugged into an outlet that's on a 15A or 20A circuit. The issue you have is that the outlet is only rated to be on a max of a 20A circuit. You can run the 8/3 to a small 4 circuit/ 2 space main lug sub-panel and use a 20A single pole breaker with 12/2 for the outlet to the auto drain and wire the Comp with 10/2 using a 30A Double pole breaker. Leaving the 8/3 fed by the 40A in the main panel.

Edit: I forgot about the outlet for the Mig. Use a larger sub-panel and put in a 40A for the Mig outlet. So the sub-panel will have a 20A SP for the auto-drain, 30A DP for the Comp and a 40A DP for the Mig.

Or just put the Comp and MIg on a 40A as you have and just add the 20A for the auto-drain.

 

[PE 316]

As currently configured, what are the consequences? (Burned-up outlet and possible fire, burned-up auto-drain, etc...)

Thanks and much respect to all!

 

[pattenp]

As currently configured, what are the consequences? (Burned-up outlet and possible fire, burned-up auto-drain, etc...)

Thanks and much respect to all!

The odds are there will never be a problem. But there's always the possibility that something can happen with the auto drain that could cause an overload and the cord would melt and catch fire before the breaker trips. All I can do is advise you that it's not proper by code.

 

[Mmbingo]

Hey guys - I have a couple follow up questions as I am in the process of the same thing...

1. Is a disconnect box required by code in all 50 states for air compressors? Does this apply to other appliances?
2. I am using 8-2G NM cable with a 40amp (240V) breaker for my comp, but the ground wire is only 10awg. Do I need 8awg wire for my ground?
3. Do I need to ground my metal receptical box??

Thanks!!

 

[sberry]

where is the breaker? Is it local? The ground wire in the cable is fine. Other things may need a disconnect if they are hard wired, breaker is out of sight etc. Yes, metal boxes must be grounded.

 

[md21722]

Outlets unless pin and sleeve type are not allowed. Outlets have both an amp and HP rating. Welding outlets, stove outlets, W/D outlets, and stuff like that are not rated for the HP. Disconnect is required when breaker is more than 50 feet away or out of sight by NEC rules.