hello guys and lady here;

i havent done writing new topic for while,,

anyway here it goes ,,

my comuster want have the semi-stationary air commpressor to be hook up with the repectale and plug in.

I did look at it and it is 7.5 hp single phase @ 240 volts 22.4 amps running amps current.

this part i am kinda relecut to do this, because i did look up the Pass and Seymour catalog book and have footnote for hp rating for 6-30R and the 6-30P they are restricted to 2 hp only and i will like your options here.

myself i rather hardwired without the plug/repectiale attachments on it. for safety reason due the current drawage and can overheat the plug at that rating.

please let me know what you think ??


merci , marc

They make motor rated outlets.

I bet if you propose that to the customer after you get a price they will hard wire.

The price for the Plug and Receptacle will change their mind!!!!

Bon jour Marc.

I agree with CDN that once they see the price they will change their mind.

I install a lot of these motor disconnect rated outlet and plug combinations,



they are high quality, easy to work with and made specifically for disconnecting motors.

You will pay for every bit of that.

For a 240 single phase 7.5 HP motor you will need a 60 amp rated device (as you have found out)

I would have to guess at a price for one wall mount outlet and one male cord cap at this size approx. $400.00 minimum

Bob



[This message has been edited by iwire (edited 04-16-2004).]

ahhh ok thanks bob and cdn for your help with this one and i did informed them about the cost for the hp rated device and they told me just go ahead hard wired it up.


many thanks for your help.

merci, marc

Hey Bob,
I'm just wondering?
Do the US receptacles of these type, have an Inter-locking mechanism in them?
As in, so that you can't attach or remove the plug, unless the supply is turned off?.
These sorts of connectors are expensive anywhere, I think, I was recently quoted NZ$350 for a set like this, the guy I was doing the job for nearly died!.

No these are not like that, they are in themselves motor disconnects.

When you plug them in first you push in a little and turn, then you push in some more against heavy spring pressure and a latch catches.

To unplug or disconnect you push on a button and the contacts spring apart but the plug is left in the outlet unless you untwist it.

You can get all kinds of accessories, Red Mushroom buttons for the unlatch button, auxiliary switch contacts that could be used as you say.

Bob

I was just reading a question on cord and plug connected air compressors at 'doityourself.com', when I remembered this thread. So I went and did some code re-reading and some calculating.

1) Air compressors, like vacuum cleaners and stereo amplifiers, often have their ratings 'pumped up' by the marketing department. I've seen '5.0 Hp' vacuum cleaners with 5-15 cord caps on their power cords.

2) 22.4A * 240V = 7.2 Hp if you presume 100% power factor and 100% efficiency, neither of which is true. Therefore this air compressor is _not_ a 7.5 Hp machine.

3) Take a look at 430.6(A)(1) exception #3: "For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, the motor full-load current marked on the name-plate of the appliance shall be used instead of the horsepower rating on the appliance nameplate to determine the ampacity or rating of the disconnecting means, the branch-circuit conductors, the controller, the branch-circuit short circuit and ground-fault protection, and any separate overload protection."

I presume that the difference is that a listed appliance has a much better defined mechanical load placed on the motor, so the listing agency can limit the startup overload and less strain is expected on the supply components.

If this compressor were sold as an integral unit with the motor built in, and the name-plate current is 22.4A, then I would think it would be just fine on a 6-30 or L6-30 receptacle.

Could someone else confirm this interpretation?

-Jon

Winnie i believe you missed part of marc's first post
quote
this part i am kinda relecut to do this, because i did look up the Pass and Seymour catalog book and have footnote for hp rating for 6-30R and the 6-30P they are restricted to 2 hp only and i will like your options here.

Un quote
Many receptacles have a HP limit in the manufacturers instructions.
You could still cord and plug connect the compressor but the cost will be high. The only real reason to do that is if the customer will be moving the compressor from place to place. Not in the case described.

nesparky,

Sorry that I wasn't clear in asking my question.

Article 430, specifically 430.6(A)(1) exception #3 clearly distinguishes between a '5hp motor' and an _appliance_ which contains a motor and has a '5hp' label on it.

This distinction carries through the sizing of conductors, selecting OCPD, sizing disconnect means, etc.

The question is: does this distinction also carry to plugs and receptacles? If I have an appliance with 15A 120V on the nameplate, can I put it on an L5-20 cord cap and receptacle, even if the appliance has a motor in it and a 6 hp label plastered to the outside?

My interpretation is that an appliance which draws 22A at 240V should be fine on a 30A receptacle. I fully agree that 7.5 hp 240V single phase general purpose _motor_ would require a much larger receptacle.

The reason that this distinction is important is that manufacturers seriously inflate the horsepower ratings of things like compressors. They don't lie, but they will plaster a '6 hp' rating on something if the power delivered at motor breakdown is 6 hp, even if the power delivered at normal full load is 2 hp. They want the high horsepower rating to make their machines seem more powerful.

Take a look at http://www.sears.com/sr/javasr/prod...ES&bidsite=CRAFT&pid=00919541000
This is a '6 hp' compressor, but if you look at the detailed specifications, the compressor is rated at 15A on a 120V circuit. 15A times 120V is less than 2.5 hp even if we assume 100% efficiency and 100% power factor. If you calculate the mechanical output power from the SCFM rating, the mechanical power output is less than 0.5 hp. For application of article 430, you simply _cannot_ consider this a 6 hp motor. Dollars to donuts this compressor comes with a 5-15 or 5-20 plug.

-Jon

You would have to be very careful playing that game. If the compressor came from Big Orange or the like, the rating is inflated to just under the point where it could be called fraud. I have a vintage Binks compressor with a compressor duty 7.5 HP motor. It draws a little better than 30 amps running. There is a lot of difference between homeowner and commercial duty. This has been interesting for me because I run mine on a 6-50 outlet and never gave the HP rating thing a thought. I've never considered it as a disconnecting means. That's what the mag starter and breakers are for. I don't think I'll change mine but I probably would not install a similar setup for a customer now.

What the manufacturers and thier salesmen do to sell is unfortunatley not covered by the NEC.
Our work is supposed to be up to at least that standard.
If the compressor comes with a set of manufacturers instruction about installation the by all means follow them. If all you have is the motor data plate then you have to use the code to determine a safe install.

Ed,

I know that you didn't mean this, and that you really meant the NEC is our standard. . .but I sure did enjoy the laugh

Al

Thanks Al
Guess i need to reread my posts to check myself.
Yes The NEC is our MINIUM standard.

wow!! many thanks for your info and help with me and in fact,, i did talk to my comusmter and he decided go with hard wire and now it work really well .


winnie: let you know this is a genral usage motor 7.5 hp @1780 rpm [ this came off from nameplate. thanks ..

merci , marc

Wowsers. Making that work would require a hefty receptacle...probably cheaper to install a 240 to 600V step up transformer, suitable (lower current) receptacle, and get a 600V motor (*grin*)

I stand by my contention that if this were a _listed_ _ampere rated_ _appliance_, that the ampere rating could be used to determine conductor size, disconnect rating, and OCPD. But given that this is a general purpose _motor_ with a _horsepower_ rating sitting on an appliance, the _horsepower_ rating is what holds sway.

In my mind, the only still open is weather the provision which permits the use of the ampere rating for the 'disconnect means' makes using the ampere rating okay for selecting a receptacle. Again, this would not apply to the present case, but I believe that it does apply to the 'big orange store' compressors.

Thanks all for a great discussion, and good news that you were able to educate your customer, marc.

-Jon