220 Air Compressor Amp Question.

[RickP]

If you use that outlet for your compressor and stand in water while touching the metal on the compressor, there's a chance the electricity would use you for a ground rather than travelling all the way back to the main panel in your house. Not good.

Just to clarify, I'm talking about electricity from 120v equipment in the garage that's using the neutral bus in your subpanel. There's a chance that electrical current could go to ground through you, rather than going all the back to the house through the neutral feed in your subpanel.

Will it happen? I don't know. Would I take a chance on it with my compressor? No way.


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[JOE.G]

So, SO I can stop bothering you guys with these questions that confuse the heck out of me, COuld you guy's post links to a Plug Outlet and cord that I can buy online to wire up the compressor? HD IS a 45 Min Hike one way for me so if I could just order online would be great.

Also the 10-50 Outlet is in a Square Metal box, would I need a new face Plate for a 6-50 Outlet?

Am I causing motor damage on the compressor by using the current 12/3 set up that seems to be working?

 

[pattenp]

Sorry... I'm not following where what I said is wrong. Reading 430.22 says to use 430.6(A)(1) to determine full load current. In 430.6(A)(1) it says to use tables (430.248). Table says 5HP is 28A and 7.5HP is 40A. I know the circuit needs to be sized at 125%. But the amps are taken from table 430.248 based on the HP rating on the motor data plate. The sizing of separate motor overload protection is done using the motor data plate current rating. I think you mistook my post. I was replying to the two prior posts to say that the amp load needs to be based on the HP. I should have been clearer in my post.


Originally Posted by pattenp View Post
By the NEC for sizing circuits you use the HP on the motor data plate, 5HP is 28A @ 230V and 7.5HP is 40A @ 230V.

WRONG!!!!!! Per NEC the wire is sized at 125% of "table amps" "Name plate" is only used for sizing the motor overloads if the motor does not have them internally.

I can not believe how many electricians do not know how to properly size a motor branch circuit.

 

[pattenp]

Cord ...
http://www.amazon.com/dp/B006NZ3S28/?tag=atomicindus08-20
Plug..
http://www.amazon.com/dp/B003X4UPFA/?tag=atomicindus08-20
Outlet...
http://www.amazon.com/dp/B00004YUNT/?tag=atomicindus08-20

You may need a new face plate. I can't remember the diameter of the 10-50.

So, SO I can stop bothering you guys with these questions that confuse the heck out of me, COuld you guy's post links to a Plug Outlet and cord that I can buy online to wire up the compressor? HD IS a 45 Min Hike one way for me so if I could just order online would be great.

Also the 10-50 Outlet is in a Square Metal box, would I need a new face Plate for a 6-50 Outlet?

Am I causing motor damage on the compressor by using the current 12/3 set up that seems to be working?

 

[RickP]

So, SO I can stop bothering you guys with these questions that confuse the heck out of me, COuld you guy's post links to a Plug Outlet and cord that I can buy online to wire up the compressor? HD IS a 45 Min Hike one way for me so if I could just order online would be great.

Also the 10-50 Outlet is in a Square Metal box, would I need a new face Plate for a 6-50 Outlet?

Am I causing motor damage on the compressor by using the current 12/3 set up that seems to be working?

Are you sure you need an outlet? How often are you going to be moving that big compressor? Could you disconnect the wiring whenever you wanted to move it?

You can order a pre-made A/C whip and wire it directly into the junction box on your wall:
10 AWG A/C Whip $11
8 AWG A/C Whip $16

Then all you'd need would be a blank faceplate for the junction box.

How big is your pressure switch? My compressor is similar in size to yours and I used the 10 AWG whip. I had trouble fitting the wires into the switch -- I don't think the 8 AWG whip would have fit.

Your compressor is overloading that 20A circuit. Sure, you can use it intermittently, but it's just not big enough for steady use.

 

[JOE.G]

I don't need a outlet but figured it would just be easier, COuld I use one of those whipes and wire it to the pressure switch then a plug?
I was looking on amazon for a Fave plate for a 6-50 Outlet but had no luck, The current one is a 2 Gang size with four screws one in each corner and then there are two in the middle that looks like it holds the outlet.

 

[RickP]

I don't need a outlet but figured it would just be easier, COuld I use one of those whipes and wire it to the pressure switch then a plug?
I was looking on amazon for a Fave plate for a 6-50 Outlet but had no luck, The current one is a 2 Gang size with four screws one in each corner and then there are two in the middle that looks like it holds the outlet.

You can wire the whip from the pressure switch into the back of the plug -- it has an opening similar to a junction box. But the whips are really made for cord, so that's a better way to go.

I just checked out your garage build - beautiful building! Where are you in NY state? I'm originally from Syracuse.

If you already have a 10-50R in that box, I think the 6-50R takes the same size face plate: Drawing

 

[pattenp]

AC whips are made for hard wiring, not to be used as a cord. The pressure clamp on the 6-50 plug is designed for a cord. I used an AC whip on my compressor hardwired to a disconnect.

View media item 16457

 

[ez-duzit]

Forget using a plug.
Forget using 12 ga.

Wire it directly using 8 ga.

 

[JOE.G]

I am not sure how to wire direct. I don't want to have a elec come back in, if I had teh parts and knew what I needed I could do the job.

I would like to keep it on a plug at least for now, I'll have to use the same outlet for a Welder also.

What Wire would I need to use it in a plug? the link above for Amazon?

 

[pattenp]

Joe, if you are going to put a cord and plug on the comp use the type cord I linked to on Amazon.

 

[JOE.G]

Ok, If I make it to HD or a Elec Supply store would they Prob carry that wire? I am guessing so. I'll Prob just order from amazon.

Now What are the Neg to Leaving it hooked up to the 12/3 and 20 Amp Breaker?

 

[pattenp]

The cord I linked to is 300V 8-3. I doubt that Lowes or HD will carry it. You will most likely need to go to a supply house. There is SOOW cord that's 600V and is a lot thicker cord. You don't really need 600V cord, but you may find that 8-3 is easier to find in 600V.

I just wouldn't leave it on the #12. I still believe it's not good for the motor in the long run due to possible voltage drop on start up.

 

[JOE.G]

Ok, Sounds good, If I wanted to Hard wire it what would I need to do that?

ANd Once again thanks to everyone for the help.

 

[RickP]

Ok, Sounds good, If I wanted to Hard wire it what would I need to do that?

ANd Once again thanks to everyone for the help.

Just buy a pre-made A/C whip and use one of the knockouts in your current junction box. You'll need three big wirenuts for the connections, then install a blank cover plate on the box. The black and red wires go to the straight blades on the 6-50P, and the green goes to the middle blade. Total cost: $12.

If you do need to move the compressor, it's not that hard to unhook the wires from the pressure switch.

 

[RickP]

Make sure the wire nuts are big enough:
Ideal 454 Blue Wing Nuts

You might be able to use a smaller one on the ground.

 

[pattenp]

Joe, when hard wiring if the breaker that supplies power is not within sight of the compressor you should have a disconnect at the compressor. If using a cord and plug, the plug is the disconnect. Look back at my picture. My breaker is in the house so I used an AC 60A non-fused disconnect.

 

[JOE.G]

I figured I would want a disconnect, I always see them near Direct wired compressors, I see people use them as the on off switch also, My Breaker box is about 20 Ft from the Compressor.

 

[ez-duzit]

...My Breaker box is about 20 Ft from the Compressor.

That's all you need. 20' is less than the length of a standard garage.

Wire it directly from the breaker to the compressor.

 

[JOE.G]

Hey guy's I picked up a 6-50 Plug, and I have some 10/3 600V Wire, In till I hard wire it ( I need the outlet also for welder ) will the 10 ga work instead of the 8 Ga? I thought you guys had said ten so that is what I got, I now came home and re read and you guys had suggested 8 Ga.

 

[ez-duzit]

...will the 10 ga work instead of the 8 Ga?...

...No...

 

[wyliesdiesels]

What is the HP rating of the compressor again? Theres TOO many posts to go back through....

 

[JOE.G]

5 HP Motor and it's under 30 Amps.

 

[pattenp]

For 5HP the NEC is 28A @ 125% which is a 35A circuit. You need #8 NM or #10 THHN.

5 HP Motor and it's under 30 Amps.

 

[wyliesdiesels]

The 6-50p wont work either as its only rated for 3HP!

 

[JOE.G]

I was told above to get the 6-50 P I am so confused.

 

[ez-duzit]

You were told to hardwire it.

 

[wyliesdiesels]

I was told above to get the 6-50 P I am so confused.

Whoever told u that wasnt aware of outlet HP ratings.

 

[JOE.G]

Yes I would like to Hard wire it, I just need to get a Parts list together, I figured for Temp I could just plug it in, I was told to use the 6-50 since that is also what a Weld would use and that it is code since a 10-50 isn't or something to that affect.

By Using the 6-50 set up what are the Neg? Is it going to cause a safety issue?

 

[pattenp]

I told him to use the 10-50 plug with #8 SJOOW cord (Post #63). And I'm very well aware of the plug only carrying a 3HP rating. I think in real life with the compressor he's got it isn't going to be a problem. If it's just temporary and he unplugs the compressor when not in use I don't see a problem. That's my opinion and it's not to the letter of the NEC.

Whoever told u that wasnt aware of outlet HP ratings.

 

[JOE.G]

Guy's I understand the correct way is to Hard wire, This is just temp in till I gave everything set up into its final Place. Of course I want it to be safe I don't want anyone to get hurt. I believe someone had said the 10-50 should be replaced with a 6-50 do to a grounding issue. SO that is what i got a I did grab 10 AWG wire where I see I should have gotten the 8 AWG which I will get when I go back to HD. Is there a Plug rated for 5 HP? If so what one ? Once again I am not looking to cause any issues and I am thankful for all of your replies.

 

[pattenp]

There is no 250V single phase plug and outlet that I know of that has a HP rating greater than 3HP.

 

[JOE.G]

How unsafe is it to hook it up with the 6-50 and either 10 AWG or 8 AWG wire?

 

[sands35]

FYI (direct link to excel file - might or might not help):

https://www.google.com/url?sa=t&rct...aCzW7FhE4zmXG1A&bvm=bv.50768961,d.b2I&cad=rja

From Square D.

Why not get a new/used safety switch off ebay? I picked one a new in the box unit for $40. 7.5hp rated at 240 VAC 1 phase. (edit - just saw that you want it to be temporary - missed that).

 

[pattenp]

Personally I'd do the 6-50 on a #8 SO cord and would not feel at all uneasy about it. I can not put a level of how unsafe it is. Have you ever driven your car without wearing a seat belt? It's probably safer than that.

How unsafe is it to hook it up with the 6-50 and either 10 AWG or 8 AWG wire?

 

[JOE.G]

I guess what I mean is what could happen, Trip breaker, Melt, Cause fire and so on.
Also would the 8 AWG and 6-50 supply the power the motor needs so it wouldn't burn out early?

The link posted above say's that I should use 10 AWG Wire, I am so confused, Elec is not my thing, I can build fix Atv's cars and what ever else but Elec just throws me off.

 

[sands35]

Probably means #10 THHN or #8 NM. They have different temp ratings. If in doubt, use THHN inside a conduit. About the same price and THHN can carry more amps at each size. Bigger wire won't hurt, just cost a bit more.

 

[pattenp]

If you were hard wiring it and using THHN wire then #10 is okay. But if you are putting a SO flexible cord with a 6-50 plug on it then I say use #8 SO. Will #10 SO cord work? Yes. Will it catch fire from being overloaded? Most likely no. Will it provide the power needed? Yes. Will the motor die early from using #10? No. The standards set by the NEC have a wide safety margin. If you are doing this for short term then I say the cord and plug will be okay. But for long term and finial installation the compressor should be hardwired. I can only advise what NEC requires. Anything less than that it's just my educated conclusion as to what will be relatively safe.

 

[wyliesdiesels]

I told him to use the 10-50 plug with #8 SJOOW cord (Post #63). And I'm very well aware of the plug only carrying a 3HP rating. I think in real life with the compressor he's got it isn't going to be a problem. If it's just temporary and he unplugs the compressor when not in use I don't see a problem. That's my opinion and it's not to the letter of the NEC.

Sorry, I always go by the NEC(in part because I HAVE to). He will probably be fine and Im sure many outlets in the world are feeding equipment that exceeds the HO rating of the outlet.

Now as far as what can happen- yes the outlet could melt!

 

[JOE.G]

Ok, COuld you guy's come up with a Parts list for me so I could pick up the stuff to Direct wire it. The Outlet is about two Ft From Compressor.

I would like to keep the outlet if I could.