220 Air Compressor Amp Question.

[RickP]

So you guys are saying I should take the 50 Amp breaker out and put either a 30 or 40 amp breaker?

Also when you get a new compressor does it come with a wire to hook to the wall?
Can I put a plug on the end or does it need to be hard wired?

How many amps can 12 3 Romex take?

Your 50A breaker should be fine for your compressor. Do you already have a 50A outlet installed on the wall? If so, you should buy a cord and plug for your new compressor that will fit that outlet. If you get other 240V equipment in the future (like a welder) you can plug it into the same outlet. (As long as you don't need to use it at the same time as the compressor.)

If you don't have a 50A outlet yet, then you could hardwire your compressor to a junction box or a disconnect (which you'd need if your compressor is too far away from the subpanel in your garage). For this setup, you should use stranded wire in flex conduit or a flexible power cord (SJ, SO, or SW cord).

 

[RickP]

Thanks to pattenp and Norcal for answers to my questions about Romex vs. stranded wire for hardwired compressors. I think I understand it now -- I'll start a new thread before I change my compressor from a temp power cord over to flex conduit.

Thanks,
Rick

 

[pattenp]

How are you coming up with the 75 ft limit with the need to up size the wire?

I just bought the sears 5hp (5.4) 80 gal compressor you were looking at. I used #10 wire and a 30 amp fuse. the compressor is 22 amp. I was told by an electrician that the compressors amps should be 80% of the fuses capacity, so 30 amp is more then enough. If you run your wire longer then 75 feet you will have to up size the wire.

 

[Mr onetwo]

Something for y'all to read...some good theory in this article.http://www.sawmillcreek.org/showthr...-breakers-for-3HP-and-5HP-shop-motor-circuits

 

[Spudland_Dave]

If you think you'll have a comp with a 7.5hp rated motor you should use the 125% and put in a 50A circuit.

Highly unlikely, but by the same token, its cheap & easy to do now...do it right, do it once is my motto. I was PLANNING on 40A Breaker, 8-3 down to my SquareD QO Shutoff (Identical to yours PattenP)

Where I get lost is the whole continuous duty thing...No bleepin way in heck would it ever run for an hour in my setting...night & weekend tinkering when the kids go to bed. So I question WHY I would need to go with 125%. I guess I wouldn't question it at all if I didn't already have 40' of 8-3 sitting here along with a 40A Breaker. The run would be 15', so going out for 15' of 6-2 wouldn't break the bank, but I now have a wasted/useless piece of wire (the 8-3)...Im trying to balance the whole Cheap *** & Do it Right equation.

 

[pattenp]

Spudland, If you do the 8-3 on a 40A breaker you'll never have an issue. That will handle a typical 5hp 60-80gal 2 stage compressor with no problems. The NEC requirement is to the extreme safety end. In most cases I see 5hp comps listing running amps in the low 20's and those would run fine on a 30A circuit, but that is in conflict with what the the NEC calls for. Don't knock yourself out over it. Use the 8-3 with the 40A breaker.

 

[JOE.G]

Yes I have a 50 Amp Outlet already mounted in the wall near, the other 220 on the 20 Amp Circuit, There both about 20 Ft from the 100 Amp sub panel. Do these Compressors come with a on off switch on them? Would I need a sub Plan or can I plug right into wall?

 

[RickP]

Yes I have a 50 Amp Outlet already mounted in the wall near, the other 220 on the 20 Amp Circuit, There both about 20 Ft from the 100 Amp sub panel. Do these Compressors come with a on off switch on them? Would I need a sub Plan or can I plug right into wall?

They usually come with a switch but no cord. You can usually buy a cord to match your outlet at the same place you buy the compressor.


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[gsmornot]

Where I get lost is the whole continuous duty thing...No bleepin way in heck would it ever run for an hour in my setting...night & weekend tinkering when the kids go to bed.

What if you forget to turn it off and leave the house. While you're gone the hose or valve pops and the compressor runs non-stop trying to fill a tank that cannot build pressure due to the leak?

 

[gsmornot]

Yes I have a 50 Amp Outlet already mounted in the wall near, the other 220 on the 20 Amp Circuit, There both about 20 Ft from the 100 Amp sub panel. Do these Compressors come with a on off switch on them? Would I need a sub Plan or can I plug right into wall?

Most of the compressors I have seen first hand come with cheap on/off switches. I'm not saying they wont work but if you turn it off and on often you might want to consider something more robust like a knife switch or just wait and see how it goes.

 

[JOE.G]

i''ll Prob pick this one up this week, Now I need Regulator help, I can' seem to find a decent one, I would like it to adjust to the full 175 PSI this Compressor will put out.

http://www.tractorsupply.com/en/store/ingersoll-randreg;-5hp-air-compressor-80-gal

 

[gsmornot]

I run my tools a little high but rarely need more than 120. You might look at a standard regulator with a "drop" prior to the regulator working directly off the tank. This would give you the full pressure plus a regulated line.

 

[JOE.G]

I may put a t in line, so I'll have the reg on one out put and a full power port. I use 1/4 NPT Fittings, but the threads off of the compressor ball valve is 3/4 Thread I think.

 

[Aceman]

Hardwire it.

A 50 amp recep only has a 3HP rating.

 

[RickP]

i''ll Prob pick this one up this week, Now I need Regulator help, I can' seem to find a decent one, I would like it to adjust to the full 175 PSI this Compressor will put out.

http://www.tractorsupply.com/en/stor...pressor-80-gal

That looks like a nice compressor.
For a regulator, you might try buying one from UPE Group. Here's the URL:
http://www.upe-group.com/


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[JOE.G]

I wired it to the 20 Amp Circuit just to try to see if it would work and it fired right up, it also fired up no problem when it had about 140 something pounds of pressure in the tank. If it is working like this can I leave it?

 

[pattenp]

The breaker not tripping isn't telling the whole story. The motor can start up but be starving for power because of voltage drop. In the long run it can damage the motor by not having a large enough circuit.

Here's a statement about wire size in the Ingersoll Rand manual....

WIRE SIZE. The electrical wiring between the power supply and
electric motor varies according to motor horsepower and other
factors. Install adequately sized power leads to protect against
excessive voltage drop during start-up.

I wired it to the 20 Amp Circuit just to try to see if it would work and it fired right up, it also fired up no problem when it had about 140 something pounds of pressure in the tank. If it is working like this can I leave it?

 

[JOE.G]

If I was to use the 50 Amp Circuit, I need to get the wire and Proper end to run from teh motor and then to the outlet, Where can I order that online? and how do I know what plug I need since 220 has a few different style plugs.

 

[pattenp]

Has an outlet been installed on the 50A circuit? If so, what's the NEMA# on it?

 

[JOE.G]

Yes there is a outlet installed, When I go out today I'll check the number, Is it on the face of the outlet?

 

[pattenp]

The number should be on the face.

 

[JOE.G]

Nema 10-50

 

[pattenp]

For the compressor get some 8-3 SJOOW cord and put a 10-50P plug on it. Be sure to use the "W" terminal/middle blade on the plug for the green ground. This isn't to the letter of NEC but it will do.

 

[JOE.G]

Thank you guys for the help, I did a Google search and Not to much came up on the 8-3 SJOOW cord, do you know of a place I could order it? Would this be some what flexible and would wire on to the plug end and then to the motor?

Also What is the Difference between a 10-50 and a 10-50P?

Would I be better off just changing the Outlet? If so what kind?

IF I keep this one I'll Have three wires correct? I am guessing Green,Black and White, You say I should put the green on the Middle which I guess would be the top Blade for the ground/Green Wire?

 

[pattenp]

The "P" stands for "Plug", "R" = "Receptacle". My bad on the SJOOW, #10 is the largest it comes in. SOOW comes in 8-3 but it is 600V wire and may be too fat to fit in a 10-50 plug. I honestly think the amp draw on that compressor will be okay with a 10-3 SJOOW cord. The 10-3 is good for 30 amps. This is why Aceman made the comment to hardwire the compressor.

 

[ez-duzit]

Hardwire it...

This. Forget the plug.

 

[RickP]

You can buy a pre-made A/C whip at Home Depot: A/C Whip

It has black/red/green 10AWG wires. Then just remove the 10-50 outlet and hardwire the compressor to a junction box.

If you keep the outlet, you can install a 10-50 plug on the end of the whip, or buy 10/3 cord instead.

 

[JOE.G]

Thanks for taking the time to help me with this, i am pretty handy but Elec is not my thing, Even if I know the answer I'll ask just to be sure.

Next time I get to HD I'll look for the above cord, I'll like to put a end on it so I can move compressor easily if need be.

Why Does the 10-50 not meet NEC code? Is it safe to use?
Should I change the outlet and get a Different plug?

From the factory it has a short wire that runs from the Pressure switch to the motor this wire states on it SOuth Wire 220V 12 AWG 600 V and is pretty fat, the Cord I wired in say's South Wire EIther 12-3 or 12 AWG I forget now 220V 300 V and it about half as think as Factory Wire.
This runs into the Romex 12-3 20 amp dual breaker outlet.

Like I said it does run fine now just not sure if I am getting Max Perf or if I am causing any kinda Motor Damage.

On Ingersols Site I found a spot where it say's for Single Phase 230V to use 8 AWG Wire, noting about Amps.

 

[ez-duzit]

8 ga, not 12.

 

[JOE.G]

EZ-Duzit what are you saying?

 

[ez-duzit]

Use the 8 ga. Pretty sure 12 ga is way too light.

 

[pattenp]

The cord you bought is half as thick because it's 300V vs. the short jump piece used from the pressure switch to the motor is 600V. The cord you got should be SJOOW where as the piece on the compressor is SOOW. You should not base the feeder circuit wiring size on the short piece used between the pressure switch and the motor.

The 10-50 outlet/plug is not the correct listed wiring device for the compressor because it is an outlet/plug listed for appliances such as a dryer or stove that uses dual voltage (125V/250V) and is considered ungrounded because technically the outlet/plug is wired using the two hots and the neutral. The neutral and ground are bonded in the appliance.

 

[hidollartoys]

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.

 

[Mr onetwo]

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.

Plus 1 on that.Motor circuits are NOT the same as wiring up an outlet or appliance.

 

[JOE.G]

Ok, so if 10-50 is not correct, what should I replace it with?
If I don't replace it is it unsafe? Will some one get shocked? Will it cause a Fire?
That circuit was put in for a Welder, is that the type of Plug they Use?

 

[RickP]

Ok, so if 10-50 is not correct, what should I replace it with?
If I don't replace it is it unsafe? Will some one get shocked? Will it cause a Fire?
That circuit was put in for a Welder, is that the type of Plug they Use?

Your 10-50 outlet isn't unsafe with your compressor if it's wired directly from the main panel of your house. But if you decide to swap it, use a 6-50 outlet that is good for most welders too.


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[RickP]

Yes I have a 50 Amp Outlet already mounted in the wall near, the other 220 on the 20 Amp Circuit, There both about 20 Ft from the 100 Amp sub panel. Do these Compressors come with a on off switch on them? Would I need a sub Plan or can I plug right into wall?

I just remembered that you have a subpanel in your garage, so you probably should swap out that outlet because it's ungrounded.


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[JOE.G]

I have 200 Amp Service in House, which feeds underground to a 100 amp panel in my Shop, the Compressor and Welder circuit runs from the 100 amp in the shop.

IF I swap out the 10 -50 would I swap the wires over to teh 6-50 one for one or do they go to different posts?

 

[JOE.G]

I have Ground Rods at the Shop off of the 100 amp Panel.

 

[RickP]

I have 200 Amp Service in House, which feeds underground to a 100 amp panel in my Shop, the Compressor and Welder circuit runs from the 100 amp in the shop.

IF I swap out the 10 -50 would I swap the wires over to teh 6-50 one for one or do they go to different posts?

The problem with the 10-50 outlet is that the middle prong should be wired to the neutral bus in your subpanel, which is not grounded at the garage. 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.

If you want to just use the 10-50 outlet you already have, you could wire it to ground instead of to neutral in the subpanel. That would be safe for your compressor, but it wouldn't be code compliant if anyone plugged a dryer into it. You could label it, but it wouldn't be safe if someone disregarded the label and used it for a dryer or oven (which would put current into the ground bus in the subpanel). So it's up to you.

Chances are, any welder you get will probably come with a 6-50 plug anyway, so you might as well swap the outlet now before buying a plug for the compressor. That's what I'd do.


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