Motor rating on outlets?

[Wade Lippman]

I just noticed that Leviton 6-20r are rated to 2hp and 5-20r to 1hp.
I bet we are all using them for 3hp and 1.5hp; is that an actual issue, or is Leviton just covering themselves?
I once used a relay on over its motor rating and it fused the contacts. Not a big deal (had to be replaced anyhow, thought I would give it a try) but I wonder what happens to an outlet.

I have sent them an email, but presume they will tell me to use their product in accord with their specifications.

[Duane Meadows]

They get hot and can burn/melt the wire insulation and/or plug. Best to stick to or below the ratings. That is pretty much why they put ratings on them. It is for your protection!

Maybe better to pay an electrician if you have a doubt in your knowledge.

[Wade Lippman]

Checking my manuals; Jet, Grizzly, Sawstop, and Rikon recommend 6-20/5-20 for their 3hp/1.5hp tools.
Are Leviton inferior to other brands? What brand has a better hp rating?

[David L Morse]

IIRC the HP rating of a plug or receptacle applies when it is used as the disconnecting device, i.e., plug or unplug to start or stop the motor instead of using a switch.

[Wade Lippman]

I contacted Leviton. They say that using it as a disconnect is irrelevant; the outlet must be rated for the motor using it.

For a 3hp motor they recommend a:
http://www.leviton.com/OA_HTML/Produ...minisite=10251 (http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=8430&section=42418&minisite=10251)

Did I get a moron, or is it true? Could Grizzly, Jet, Sawstop, and Rikon be recommending unsafe outlets?
Or is Leviton's 6-20 inferior to others?

[Sam Stephens]

????? didn't know receptacles cared about hp. thought it was about current draw. 6-20r is rated for 240VAC/20amp. What's the current draw of your motor ~10amp? Ought to be fine.

Their "recommended" receptacle is for a 3-phase motor, so yes there was a "disconnect" somewhere....it's wrong. Perhaps an electrician would be a good idea here, no?

[Matt Marsh]

Wade, the manufacturers must rate these devices for continuous duty. The minimum circuit ampacity for a 3 hp motor wired for 230 volts is over 20 amps. The FLA rating From NEC table 430.248 is 17 amps, but it must be calculated at 125%. 17 X 1.25 = 21.25 amps. The same is true for the 1.5 hp motor wired for 115 volts. The FLA value from table 430.248 for it is 20 amps. 20 X 1.25 = 25 amps.

[Matt Marsh]

By the way, the link you provided for the recommended device shows a NEMA 15-30 device, which is a 4-wire device. You probably want a 5-30 device, which are 3 wire.

oops! You probably want a 6-30 device for the 230 volt config., and a 5-30 for the 115 volt.

[Wade Lippman]

Wade, the manufacturers must rate these devices for continuous duty. The minimum circuit ampacity for a 3 hp motor wired for 230 volts is over 20 amps. The FLA rating From NEC table 430.248 is 17 amps, but it must be calculated at 125%. 17 X 1.25 = 21.25 amps. The same is true for the 1.5 hp motor wired for 115 volts. The FLA value from table 430.248 for it is 20 amps. 20 X 1.25 = 25 amps.

If I understand you correctly, you are saying it is a technical matter that doesn't really affect hobbyist woodworking equipment. An 18a 3hp Grizzly jointer is okay on a 6-20?
What is "continuous duty"?

Leviton sent me the link to the 15-30 and told me it was what I should be using because it was rated for 3hp. He specifically said that using a 6-20 with a 3hp woodworking machine could lead to a house fire.

[David L Morse]

Leviton .... specifically said that using a 6-20 with a 3hp woodworking machine could lead to a house fire.

Based upon that statement


Did I get a moron, ....?

it would appear so.

[Matt Marsh]

If I understand you correctly, you are saying it is a technical matter that doesn't really affect hobbyist woodworking equipment. An 18a 3hp Grizzly jointer is okay on a 6-20?
What is "continuous duty"? Well no, you should wire it to meet the minimum requirements of all the manufacturer(s) listings, and the NEC. If the HP and or amp rating of the plug and receptacle is not high enough for your particular motor, you need to jump up to the size that will cover it. Continuous duty is generally considered to be when a machine is operated continuously for 3 hours or more. But if the listing on your motor nameplate states that it is a continuous duty motor, then that starts getting a bit gray. You're better off erring to the larger sized circuit, plugs, and receptacles. Manufacturers these days are notorious for under-rating supply cords. Why and how they are getting away with it is a mystery. For example, NEC table 210.21(B)(2) lists the maximum cord and plug connected load to a 15 amp receptacle at 12 amps. That's 1440 watts maximum for a 120 volt load, yet hair dryers with 15 amp configured plugs rated in excess of 1800 amps are the norm these days.


Leviton sent me the link to the 15-30 and told me it was what I should be using because it was rated for 3hp. He specifically said that using a 6-20 with a 3hp woodworking machine could lead to a house fire.A 6-20 NEMA configuration is for a 2-pole, 3-wire, 250 volt single phase circuit. It has provisions for two hots, and one equipment ground. A NEMA 15-30 configuration is for a 3-pole, 4-wire, 250 volt 3-phase circuit. It has provisions for three hots, and one equipment ground. If you are merely increasing the ampacity size of the circuit, you would go from a 6-20 configuration, to a 6-30 configuration, if it has the required HP rating also. 267592267593

[Matt Marsh]

Wade, I just noticed that even the 6-30 plugs at Graingers are only listed for 2HP. I'll do some checking.

[Duane Meadows]

That's 1440 watts maximum for a 120 volt load, yet hair dryers with 15 amp configured plugs rated in excess of 1800 amps are the norm these days.



1800 Amps? Wow! That would burn the hair of your head in hurry!

[Jim Neeley]

Mark,

As you research deeper I think you'll see that the electrical plugs are technically rated by max voltage and rated current (plus temp). Rating them by horsepower makes no strict sense since that would imply a motor efficiency, amongst other things and that the rating is "lawyer-speak" to limit liability. All they have to do is to choose a low enough number and they figure they're protected.

That reminds me of an umbrella I once purchased that had a cloth tag inside saying "NOT TO BE USED AS A PARACHUTE".. Duh! <g>

Motor circuits are strange beasts. As I posted in another thread, I purchased a "5hp" new-style Delta Unisaw with a Marathon motor rated at 20FLA @ 240VAC single phase that came with a 6-20P factory-attached and instructions to connect it to a 6-20R with #10 wire and a 40A breaker.

This made no sense to me so I discussed this with Jim Stallcup (Senior Member, NFPA70 [NEC]), an Intertek field-listing agent and my local inspector. All told me that it was OK to install per their instructions as the saw had been tested and approved for that configuration, containing internal motor protection and all I was doing was to protect the wiring. I debated replacing the plug with a 6-30P but figured it'd muddle up the warrantee so did as told.

Jim in Alaska (a fellow EE-PE)

[Matt Marsh]

1800 Amps? Wow! That would burn the hair of your head in hurry!
Oops! LOL! Yeah all on a #14 twin lead cord!

[Wade Lippman]

After spending way too much time on it, I think I have a satisfactory answer.

All the woodworking machinery manufactures say they have never heard of rating outlets by HP, as long as you are within the current rating you are fine. No one has ever experience a problem.

Leviton says the HP rating must be adhered to, whether the outlet is used as a disconnect or not; or a fire might result.
Hubbel says it depends on the controller; if the machine has a controller it should be fine. I said I had heard that maybe the HP rating is when the outlet is used as a disconnect. He agreed with that; if there was a switch it was okay. I have never heard of a switch being called a controller, but I guess that is okay.
Cooper said their outlets did not have HP ratings (despite the fact they do...). Since they don't have starter contracts HP rating wouldn't make sense. That seems to be saying they shouldn't be used as disconnects.

So my conclusion is that the two people I spoke to at Leviton didn't know what they were talking about; as long as you don't use the outlet as a disconnect, the HP rating does not apply.