Wiring 60 gallon Air Compressor

[phalanx]

Hi all,

I've got a US General (older refurb) 60 gallon air compressor from Harbor Freight being delivered in the next couple of days and want to get the wiring done before it arrives. I'm planning to run wire from the breaker panel to the garage and connect via an outlet since I'm replacing a large section of drywall and have access to the stud to mount a box anyway.

I purchased a 40 amp breaker which matches the manufacturer brand of the others in the panel, 50ft of 8/2 wire, a 50A outlet (I've never seen a 40A outlet so I went larger) and an appliance cord. The problem is that the cord is a 4-prong since they didn't have any 3-prong in stock so I got a 4-wire 50A outlet to fit. My question is, can I use just the black, red and ground wires from the cord to connect to the compressor to plug in to the outlet and cap off the white neutral then run wire from the panel to the outlet and connect both hot wires and the ground and leave the the white neutral slot empty in the outlet since it's only an 8/2 wire? I don't plan on connecting anything else in the garage but wondering if this violates any codes? I can get a 3-wire 50A outlet and order a 3-prong appliance online I suppose but would like to get this done with everything I have now if possible (and safe!)

I've been searching for threads and youtube videos of air compressor installs but can never make out how the appliance cord/outlet is wired if it's not being hardwired.

Thanks

 

[md21722]

The problem with using the appliance plug is that while it has the amp rating, it does not have the HP rating. Sounds like you have the true 5HP Harbor Freight model, you use of 8/2 is just fine. Hard wire it if you can. By code, if panel is more than 50 feet or out of sight you'd need a disconnect. If you need the disconnect its an easy way to transition to THHN in flexible conduit to the compressor. You can use #10 THHN for this.

 

[phalanx]

OK, I can do a disconnect panel and hardwire it if that is the best option. Does the disconnect panel need to be the same brand as everything else? In my case it's Square D QO (the older version, not the newer Homeline).

I've never installed a disconnect panel before so I have some basic questions.

Does it have to be a 40A disconnect that connects to the 40A breaker in the main panel? It looks like the big box stores only have 30A, 50A and 60A disconnect panels.

Fusible or Non-Fusible?

Metallic or Non-Metallic casing? (assuming it doesn't matter since it's in the garage)



EDIT: It looks like I'm in the exact same situation as this guy -

He’s using a 30A breaker in the main panel and a 60A disconnect to hardware to his compressor.

 

[zak77]

I used a very similar setup when i wired up my Husky 60 gallon 3.7hp compressor except i made my own cord with the same plug end since i installed the same outlet. The outlet is hooked up to all 4 wires(2 hots, neutral and ground) however i used 10/2 wire since it only pulls 15 amps. Not sure how many amps your compressor will pull but as long as the wire is rated for it, i don't see a problem with the setup since mine is the same.

 

[phalanx]

The manual says the full load amps is 23 but it recommends a 40A breaker for whatever reason. I guess it spikes over 30A on startup? As much as I don't trust HF documentation, I figured I might as well follow it for something big like this.

How did you wire the outlet with all 4 with only 10/2 wire or do you mean you used 10/2 from the compressor to the outlet? I didn't see a standalone plug that was over 20A at the store to make my own cord.

 

[zak77]

I had extra 10/2 wire so i made the cord with the same plug you have but i used 8/3 for the run from the outlet to the 50amp breaker. I also run a 220v MIG off the outlet so i over-sized the line just in case i wanted a bigger welder in the future. The mig doesnt pull all that many amps, maybe 25-30 or so? Hobart 210mvp. I had to make a cord for the welder also. I found the 50 amp plug at the hardware store.

https://www.lowes.com/pd/Utilitech-50-Amp-125-250-Volt-Black-4-Wire-Grounding-Plug/4068225

 

[pattenp]

For a general use outlet, 8/3 romex is only rated to be on a max of a 40A breaker.

 

[md21722]

There is a "general rule" that some compressor manufacturers use that says size the breaker to 178% of FLA which in your case would be about 40A.

By code, you'd be sizing the wiring to 125% of FLC of a 5HP motor, that's 28A X 125% = 35A (#10 THHN or #8 NM-b) and then the breaker can be 250% of FLC (70A in your case) as long as thermal protection is present (either in the motor, i.e. red button reset, or via a motor starter with overloads). Note that FLC is what it is the NEC tables and is based on HP, not motor nameplate.

So you're correct to use the 8/2 and a 40A breaker would be fine.

Circuit breakers are designed to allow the startup (also know as locked rotor) current which is usually 5-6X nameplate. A 5HP single phase motor generally has a startup current of 130-170A. The motor manufacturers list this value in their spec sheets if you were interested in looking it up.

I have true 5 HP compressors at home and run them off 30A without any nuisance tripping.

 

[pattenp]

Oversizing the breaker on motor circuits is only allowed when hardwired.

 

[wyliesdiesels]

The manual says the full load amps is 23 but it recommends a 40A breaker for whatever reason. I guess it spikes over 30A on startup? As much as I don't trust HF documentation, I figured I might as well follow it for something big like this.

How did you wire the outlet with all 4 with only 10/2 wire or do you mean you used 10/2 from the compressor to the outlet? I didn't see a standalone plug that was over 20A at the store to make my own cord.

Motors have inrush current.

Standard NEMA outlets are rated to about 3HP.

10/2 NM-b has 2 insulated conductors and 1 bare copper for ground.

But 10/2 is too small for your compressor as explaind above.

 

[phalanx]

Thanks everyone for the information thus far, this thread is tremendously helpful.

I ran to a different HD store today to look for a 40A Square D QO disconnect panel and they were out as well. The guy recommended this plug which he said people use for welders and compressors all the time - http://www.homedepot.com/p/Leviton-...ight-Blade-Plug-Black-R50-00931-000/202077682

Then walked me over to the area where they cut the wire by the foot and showed me some that was over half an inch thick that had 10/2 gauge copper wiring in it (each of the 3 strands were 10 gauge). It looked a lot larger than the appliance cord I got from Lowe's originally. Assuming I can't find a Square D disconnect panel, would this set up work as an outlet disconnect? I really want to hard wire it but it's not looking like I'm going to find the panel unless I can use a different brand and a different breaker size?

 

[md21722]

The only ones that are rated for over 3 HP are pin and sleeve. Try your local supply house or Amazon or someplace like that for the disconnect. I don't see a reason that the disconnect needs to match the panel brand.

 

[pattenp]

Picture is a Square-D QO200TR which can be purchased at HomeDepot or Lowes for about $16. It is a nonfused 60A A/C disconnect switch and is rated at 10HP. If your compressor motor is more than 3HP then a standard NEMA plug is not appropriate as a disconnect.

This is how I hardwired my compressor.
View media item 16457

 

[jim111]

OP It does not matter if your disconnect is the same brand as your panel, it just has to be rated at least as much as your circuit, fused is not necessary. The one pictured by pattenp is a good example of what you need

 

[wyliesdiesels]

Thanks everyone for the information thus far, this thread is tremendously helpful.

I ran to a different HD store today to look for a 40A Square D QO disconnect panel and they were out as well. The guy recommended this plug which he said people use for welders and compressors all the time - http://www.homedepot.com/p/Leviton-...ight-Blade-Plug-Black-R50-00931-000/202077682

Then walked me over to the area where they cut the wire by the foot and showed me some that was over half an inch thick that had 10/2 gauge copper wiring in it (each of the 3 strands were 10 gauge). It looked a lot larger than the appliance cord I got from Lowe's originally. Assuming I can't find a Square D disconnect panel, would this set up work as an outlet disconnect? I really want to hard wire it but it's not looking like I'm going to find the panel unless I can use a different brand and a different breaker size?

I couldnt find a HP rating for the leviton 931 u linked to. However as is the case for NEMA plugs i doubt its rated more than about 3HP.

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=931&section=41808&minisite=10251

Furthermore, it may not have a HP rating at all as its not in the Leviton power plug line of wiring devices.

Leviton has another 6-30p that IS in the power plug line and is rated for 2HP....

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=9630-P&section=42417&minisite=10251

U should hardwire the compressor....

 

[mikhett]

I have a Husky 7hp 2 stage compressor I used 8/2 and a disconnect like PATTEN P.IM ONLY 2 FEET FROM THE SIEMANS sub panel.Its rated @ 23 amps.

 

[phalanx]

Thanks again everyone, I saw plenty of 60A disconnect panels on the shelf so I can grab one tomorrow. The compressor should be delivered in the morning. I assumed the breakers in the disconnect box and the main panel had to be the same amps so I was strictly looking for a 40A Square D box which nobody seems to have in stock.

This is how I hardwired my compressor.
View media item 16457

Is that rubber flexible conduit? What kind of wiring did you use?

 

[pattenp]

The Square-D QO200TR pictured is a disconnect switch, it is not a breaker. A breaker is not needed in the disconnect. The 60A listing is not overcurrent protection, it's the current the switch can handle. Plus the switch is listed as being rated for up to 10HP.

The conduit is a #10 THHN/THWN A/C whip. Liquidtight conduit is the same and you buy the wire separate.
http://www.homedepot.com/p/AFC-Cable-Systems-Liquidtite-10-3-in-x-6-ft-AC-Whip-8015-HD/202286686

Edit: You can use the #10 AC whip for 40A because the wire is THHN/THWN and can be sized by 75deg C. Your romex needs to be #8 for 40A because it's 60deg C wire.

*

 

[phalanx]

Edit: You can use the #10 AC whip for 40A because the wire is THHN/THWN and can be sized by 75deg C. Your romex needs to be #8 for 40A because it's 60deg C wire.

Perfect! An AC whip would be cheaper than buying everything separate and putting it all together so I'll go that route. Of course the HD a couple miles down the road doesn't have any in stock but the one across town does. However, Lowe's has 10 and 8 gauge AC whips in stock but the specs say that the max amps for the #10 whips is 30A and #8 is 40A. Since you say it can be sized by 75C I can get either I suppose?

https://www.lowes.com/pd/Southwire-...tor-Non-Metallic-Liquidtight-A-C-Whip/3616544

https://www.lowes.com/pd/Southwire-...tor-Non-Metallic-Liquidtight-A-C-Whip/3616542

 

[pattenp]

I'd just go ahead and get the #8 since you are wiring it for 40A. The #8 may be a little tough hooking up to the pressure switch.

 

[wyliesdiesels]

I have a Husky 7hp 2 stage compressor I used 8/2 and a disconnect like PATTEN P.IM ONLY 2 FEET FROM THE SIEMANS sub panel.Its rated @ 23 amps.

At 23a FLA its more likely a 5HP compressor.

Many manu grossly overrate and inflate the HP ratings...

8/2 NM-b would be too small for a 7HP compressor.

 

[wyliesdiesels]

Perfect! An AC whip would be cheaper than buying everything separate and putting it all together so I'll go that route. Of course the HD a couple miles down the road doesn't have any in stock but the one across town does. However, Lowe's has 10 and 8 gauge AC whips in stock but the specs say that the max amps for the #10 whips is 30A and #8 is 40A. Since you say it can be sized by 75C I can get either I suppose?

https://www.lowes.com/pd/Southwire-...tor-Non-Metallic-Liquidtight-A-C-Whip/3616544

https://www.lowes.com/pd/Southwire-...tor-Non-Metallic-Liquidtight-A-C-Whip/3616542

I wonder what type of wire is used in those.

If its THWN then Lowes is wrong about the amperage rating which wont be the first time.

 

[phalanx]

I wonder what type of wire is used in those.

If its THWN then Lowes is wrong about the amperage rating which wont be the first time.

Yeah, the Lowe's website is not only buggy but I've found numerous incorrect specs for quite a few other items in the past. I just (obviously) don't have much electrical knowledge and trying to get this little project done ASAP. Anyway, I just got back from Lowe's and the green is #10 THHN and the black and red are #8 according to the packaging. I ended up getting the 1/2" whip with #10 black/white and green stranded wire.

 

[pattenp]

I wonder what type of wire is used in those.

If its THWN then Lowes is wrong about the amperage rating which wont be the first time.

The conductors are THHN/THWN and the #10 is listed as 30A and #8 as 40A on the Southwire product site. I'm sure they list the lower amp rating at 60deg C or based on the small conductor rule not knowing what the actual product will be used for.

 

[wyliesdiesels]

The conductors are THHN/THWN and the #10 is listed as 30A and #8 as 40A on the Southwire product site. I'm sure they list the lower amp rating at 60deg C or based on the small conductor rule not knowing what the actual product will be used for.

Its probably for liability reqsons why they do that.

 

[phalanx]

Sorry for the delay on this but wanted to give a quick update. I got the air compressor delivered and wired with the #10 THHN AC whip and a Square-D QO200TR just like pattenp has. I started running the 8/2 romex from the main panel to the garage but I need to finish hanging some drywall first before I mount the disconnect panel.

I'm not sure what to do regarding the condition of this "factory reconditioned, factory perfect" air compressor though. The motor and pump both seem to be brand new (no dirt or rust or anything) in fact, I think the unit was a return after never being used and just sat in a warehouse. My concern is the scratches on the front which are down to the metal and the fact that the electrical cord is taped and kinked like that. I guess it was severed at some point. The whole thing was wrapped nicely and mounted to a large pallet so I think these are all pre-existing conditions but I would think a refurb would at least get a new cord and touch-up paint. I got this thing for a little over $500 so I can live with it, just not sure about electrical tape on a cord that thick lol.

 

[pattenp]

Just get some spray paint and touch up that spot so rust won't set in. I think I would replace the cord. Kind of hokey that it wasn't replaced instead of being taped up.

 

[wyliesdiesels]

Dont think thats the correct wire either.

I usually see #12 wire rated at 105* c when used on 5HP motors.

 

[phalanx]

OK, Harbor Freight are going to send a replacement air compressor and pick this one up to go back to the warehouse. It's probably going to be another 2 weeks but I have everything wired now so I should be good to go.

Regarding this set up though, can I replace the 60A breaker that came in the paenl disconnect switch with a 40A one? When I was inspecting my main panel, I noticed there was an old 60A breaker looks kind of old and crusty so was thinking I could replace it with the one that came in the disconnect panel and put in a new 40A. That way I will have the compressor wired with #10 THNN AC whip to a 40A disconnect then #8 romex to the 40A breaker in the main to keep everything consistent.

 

[wyliesdiesels]

OK, Harbor Freight are going to send a replacement air compressor and pick this one up to go back to the warehouse. It's probably going to be another 2 weeks but I have everything wired now so I should be good to go.

Regarding this set up though, can I replace the 60A breaker that came in the paenl disconnect switch with a 40A one? When I was inspecting my main panel, I noticed there was an old 60A breaker looks kind of old and crusty so was thinking I could replace it with the one that came in the disconnect panel and put in a new 40A. That way I will have the compressor wired with #10 THNN AC whip to a 40A disconnect then #8 romex to the 40A breaker in the main to keep everything consistent.

U can only do that if the replacement breaker is listed and labeled for use in the breaker panel.

What is the brand and model of panel and the brand of breaker and model of breaker?

 

[phalanx]

U can only do that if the replacement breaker is listed and labeled for use in the breaker panel.

What is the brand and model of panel and the brand of breaker and model of breaker?

Both are Square D QO

Panel - https://www.lowes.com/pd/Square-D-60-Amp-Non-Fusible-Metallic-Enclosed-Circuit-Breaker/3364886

40A Breaker - https://www.lowes.com/pd/Square-D-Qo-40-Amp-2-Pole-Double-Pole-Circuit-Breaker/3129467

 

[Jrad235]

I had the same issues with the cord on mine, except it was almost completely severed. The edge of the motor plate lends itself well to cutting that cord if it bangs into something. Rather than drag it back to the store, I replaced it myself.

 

[ToddW]

Why use the Non-Fusible Enclosed Circuit Breaker?

Why not spend a little more and get a magnetic starter to make sure the pressure switch stays safe and no fires, and then you can wire in a switch near your lights?

I think you can get some USA Made 5HP rates ones ~50-75$.


Just thinking out loud, and another option instead of the non-fused CB?

Came my mind as I recall my pressure switch melting the cover after a wire got lose OR from it kicking on and off during a project then smoke smoke smoke melt down as it wore out the pressure switch? I don't know exact cause but the wire wasn't dangle / lose just could have not been snug enough

 

[Norcal]

OK, Harbor Freight are going to send a replacement air compressor and pick this one up to go back to the warehouse. It's probably going to be another 2 weeks but I have everything wired now so I should be good to go.

Regarding this set up though, can I replace the 60A breaker that came in the paenl disconnect switch with a 40A one? When I was inspecting my main panel, I noticed there was an old 60A breaker looks kind of old and crusty so was thinking I could replace it with the one that came in the disconnect panel and put in a new 40A. That way I will have the compressor wired with #10 THNN AC whip to a 40A disconnect then #8 romex to the 40A breaker in the main to keep everything consistent.

It is not a circuit breaker in that SQ D disco, it is a molded case switch, do not install it in a panel.