Compressor Outlet

[bczygan]

2HP 230V 12A 1PH Sears compressor on wheels (See photos).

Motor has built in overcurrent protection (Red button).

Motor is continuous duty 40C, insul. B.

Panel is 20' from receptacle.

In addition to cord on the machine, I will be using a 40' extension cord of #12.

First, sizing the branch circuit conductors:
I see that in 430.238, a 2HP 230V 1PH motor is rated at 12FLA. At 125% that's a 15A circuit and #14 wire.I'd like to use a 20A circuit and #12 THHN in PVC conduit. That should take care of conductor sizing.

For Branch-circuit protection for short-circuits and ground-faults, the breaker can't exceed 250% of nameplate FLA. Here that is 12A so breaker max is 30A.

Are we good so far?

What 20A outlet may I use for this circuit? Must it be rated for a 2HP motor?

Bill

 

[Norcal]

Can't use a 30A breaker on a 20A receptacle.

 

[mm08822]

This is actually funny!!

You need a 6-20R b/c it's rated for 2hp with 2P 20a cb and #12 wire.

 

[bczygan]

Can't use a 30A breaker on a 20A receptacle.

I thought you oversized breaker up to 250% for inrush current for a compressor.

Bill

 

[sberry]

It can be but it cant go on a recept not rated for the breaker. Use a 10 wire to a 30 and a 30 recept and its legal provided the unit has its own thermal and a 14 or better cord.

 

[sberry]

Correction,,,,,, May be legal,,,,,,, but if it comes with factory end on the cord that is the outlet that should be used and max legal breaker.
This is the reason for the cord end design. A guy simply plugs it in to the proper circuit. Reading the code is a good learning exercise but it's not a how to guide for those not familiar with it and Nema etc.

 

[bczygan]

It can be but it cant go on a recept not rated for the breaker. Use a 10 wire to a 30 and a 30 recept and its legal provided the unit has its own thermal and a 14 or better cord.

Correction,,,,,, May be legal,,,,,,, but if it comes with factory end on the cord that is the outlet that should be used and max legal breaker.
This is the reason for the cord end design. A guy simply plugs it in to the proper circuit. Reading the code is a good learning exercise but it's not a how to guide for those not familiar with it and Nema etc.

Well, this compressor had the plug changed to a standard 1P 20 amp by the previous owner, an electrician.

And I suppose the way to start is to install a 20A receptacle and see if it trips.

But shouldn't it be #12 either way?

Bill

 

[Norcal]

I thought you oversized breaker up to 250% for inrush current for a compressor.

Bill

A receptacle is limited to it's rating.

 

[sberry]

If it is on a 20A circuit with a 20A outlet, if it's on a 30 and a 30 recept then 10. If it was hardwired it may be able to use 12. You can't leave this recept for further potential use with the wrong wire.
From a pure safety perspective for use with this machine it's not a problem but it's not a compliant installation.

 

[alfredeneuman]

If it was hardwired it may be able to use 12.

If the motor was hardwired, why couldn't you use a #14?

 

[Norcal]

But why would you want to hard wire a portable compressor? That was the primary reason that never brought up hardwiring it

 

[sberry]

If the motor was hardwired, why couldn't you use a #14?

he asked about 12.

 

[American Locomotive]

Really over thinking it. Just wire in a NEMA 6-20 outlet, with 12 gauge wire and a 20A breaker. It's a 2HP motor, not a 200HP one. It's very unlikely to trip a 20A breaker.

 

[bczygan]

So let me understand the rule.

Circuit is to be at least 125% but not more than 250% of the motor FLA? And then the nearest breaker and corresponding wire to accomplish that?

So I could use #12 with a 20 or #10 with a 30? But the outlet would need to match and be HP rated?

Could larger wire be used with a smaller breaker and outlet?

Bill

 

[sberry]

The man above made it clear as can it can get.

 

[sberry]

All that is mostly for larger equipment that does not come cord and plug where the mechanic must determine the installation.

 

[theoldwizard1]

Really over thinking it. Just wire in a NEMA 6-20 outlet, with 12 gauge wire and a 20A breaker. It's a 2HP motor, not a 200HP one. It's very unlikely to trip a 20A breaker.

CONCUR !

I have the slightly newer version of the same compressor (tan, not green). It has been running off of a pair of 20A FUSE for over 30 years.

The power cord Sears gave you iss stupid short. I removed the cord at the switch and installed a 25' SJOOW cord and 6-20 plug. Never been a problem. Just got done using it 10 minutes ago.

 

[bczygan]

I am going to wire it up as a 20A circuit, but trying to understand it for larger HP.

Say it was a 3 or 4 HP.....

As an example, could I wire this circuit with say, #8 or #10 and a 20A breaker and outlet for this compressor?

That way, later I could just change breaker and outlet for a bigger one.

Bill

 

[manwithtools]

You could as long as the lower amperage outlet and breaker are rated for terminating the larger wire. For instance, a 20 amp outlet may not be rated to accept an 8ga wire under it's screw clamp. I'm to tired to look it up just now.

 

[sberry]

Yes but why fuk with all that? Make it work, get it going, use the thing vs worrying obsessively about "what if" that has a good chance of never happening. Convert this circuit if it should be the case to 120 later and if it actually happens get another wire.
I been at this a while, I cant even remember the last time I actually used a future proof idea I had, in fact by that time the design changed, the stuff became obsolete and it was all useless. I still have a lot of wire "parked" I have never used, I put in just in case. Could hav3e used it when some place I did need it came along and I had to buy more.
As the Old Guy above said,,,, wayyyyyyyyyy overthinking this.

 

[theoldwizard1]

As an example, could I wire this circuit with say, #8 or #10 and a 20A breaker and outlet for this compressor?

That way, later I could just change breaker and outlet for a bigger one.

#10 and a 30A breaker would easily cover a 3-4 hp compressor and any compressor with a high efficiency 5hp motor.

 

[Aceman]

#10 and a 30A breaker would easily cover a 3-4 hp compressor and any compressor with a high efficiency 5hp motor.

A 30 amp breaker isn't legal for a true 5HP 230v single phase motor.

 

[wyliesdiesels]

So let me understand the rule.

Circuit is to be at least 125% but not more than 250% of the motor FLA? And then the nearest breaker and corresponding wire to accomplish that?

The wire is to be 125% of NEC FLC table amps. For a 5HP FLC of 28a this means 35a rated wire. Code requires sizing based on HP and table FLC NOT motor nameplate FLA.

The breaker has no minimum just a max of 250% of table FLC so 70a for 5HP.

But the 250% max breaker size only applies to hardwired motors. Cord and plug connected motor circuits MUST have a breaker that matches the outlet.

So I could use #12 with a 20 or #10 with a 30? But the outlet would need to match and be HP rated?

Could larger wire be used with a smaller breaker and outlet?

Bill

Yes the outlet needs to be rated for at least the same HP as the motor.

Yes you can always oversize the wire but why would you unless the run is very long. You also have to keep in mind that outlets have a max gauge of wire they can accept.

 

[bczygan]

The wire is to be 125% of NEC FLC table amps. For a 5HP FLC of 28a this means 35a rated wire. Code requires sizing based on HP and table FLC NOT motor nameplate FLA.

The breaker has no minimum just a max of 250% of table FLC so 70a for 5HP.

But the 250% max breaker size only applies to hardwired motors. Cord and plug connected motor circuits MUST have a breaker that matches the outlet.



Yes the outlet needs to be rated for at least the same HP as the motor.

Yes you can always oversize the wire but why would you unless the run is very long. You also have to keep in mind that outlets have a max gauge of wire they can accept.

Been waiting for you to chime in!

How do you determine HP rating of outlets?

Online listings for big box stores don't mention that.

Bill

 

[mm08822]

How do you determine HP rating of outlets?

Online listings for big box stores don't mention that.

Bill

A lot of times the product details are incorrect, full of many typos or still doing the marketing campaign on the big box websites. 2 items I checked from big box didn't even list hp whatsoever. Always go to the mfr. See below.......

 

[Matt Matt]

Been waiting for you to chime in!

How do you determine HP rating of outlets?

Online listings for big box stores don't mention that.

Bill

I use Hubbell...
http://ecatalog.hubbell-wiring.com/...ubbell-wiring.com/press/catalog/A.pdf&Page=11

 

[Bert_]

CONCUR !

I have the slightly newer version of the same compressor (tan, not green). It has been running off of a pair of 20A FUSE for over 30 years.

The power cord Sears gave you iss stupid short. I removed the cord at the switch and installed a 25' SJOOW cord and 6-20 plug. Never been a problem. Just got done using it 10 minutes ago.

Bit of a side note. If that is a time delay fuse, it will tolerate quite a bit more startup current than the same sized breaker.

But in this case, a motor that draws only 12A and an air compressor that doesn't have a whole lot of rotating weight = not much startup draw, A 20A breaker should work just fine.

You really only need to use the max breaker sizes allowed by code when the motor takes ~10-20 seconds to get up to speed.

 

[American Locomotive]

I've pulled a measured 180 amps (this particular motor had insane startup current) through a 30A breaker without tripping it. I was doing a quick test of a motor-generator welder I picked up, and just wanted to make sure it spun up.

 

[wyliesdiesels]

I've pulled a measured 180 amps (this particular motor had insane startup current) through a 30A breaker without tripping it. I was doing a quick test of a motor-generator welder I picked up, and just wanted to make sure it spun up.

My 3 ton AC compressor with an FLA of 11 pulls 100a on startup measured with a fluke 381 (has an in-rush current measurement capability; not all meters do) In-rush current is typically the first 100-200ms of the startup cycle.

 

[bczygan]

Thanks everyone!

I'm good to go. Now to find an inexpensive QO breaker source.

Bill

 

[Norcal]

Thanks everyone!

I'm good to go. Now to find an inexpensive QO breaker source.

Bill

"Inexpensive QO breaker" ? SQ D is very proud of their merchandise, so good luck.

 

[sberry]

The box store is best. This is a point I was working on in another post in this thread. No point in spending a 30$ extra,, or more for number 8 wire just in case,,,, then delaying the use of it so you can save 3 dollars on a breaker. This is a classic case where the whole scheme should have been done Homeline right from the start.

 

[Bert_]

Most breakers are the "inverse time" type, meaning the more current you pull the faster it will trip. It is also true that the shorter the duration the more current you can pull without tripping the breaker.

Many breakers also have a magnetic trip, meaning once you pull more than a certain amount of current they will trip instantly. I think that would be somewhere around 10 times the rated current?

As a bit of coincidence I was just explaining this to someone earlier in the week. I put an amp meter on a 10hp 1 phase fan and it drew 230A and settled down to 35A over about 10-12 seconds. This fan had a ~50lb blade so it does take a bit to get up to 1750RPM. It had an FLA of 38A and I put it on a 100A breaker.

I would think you could find a 2p 20 for 15-20 bucks, they aren't that expensive.

 

[bczygan]

Lowes:

$10 for the plug
$5 for the outlet
$15 for the QO breaker
I have the wire, 12 AWG THHN THHW in green, black, white and red.
Surface mount PVC box and metal cover plate
Some PVC conduit and fittings for same
Less $20 off $50 Lowes coupon code

= Happy!

Bill

 

[bczygan]

By the way,

Should the 3 wires be black, red and green?

Bill

 

[sberry]

That works, black black and green works too. Could use red red and green too.

 

[American Locomotive]

black and red is fine.

 

[wyliesdiesels]

By the way,

Should the 3 wires be black, red and green?

Bill

There is no color code for ungrounded conductors... only grounded and grounding conductors...

 

[bczygan]

You guys are the best!!!

Bill

Next I want to install my own pole mounted transformer and CT cabinet.......!

 

[Norcal]

There is no color code for ungrounded conductors... only grounded and grounding conductors...

Although it does not apply to the discussion in this thread, the one place the NEC does specify a color for a ungrounded conductor is orange for the high leg of a 240V 3Ø supply.