Dual voltage receptacle

[David Meiland]

I've got a Hubbell floor box in my shop slab, with a brass trim for a duplex receptacle.

Getting ready to trim it out, I was looking for something like this:

http://www.leviton.com/OA_HTML/ibeCC...&section=10928

The receptacle is going in the floor behind and beneath a 3HP 240V tablesaw that has a 120V dust collector as an accessory. My goal is to plug both items into the receptacle, feeding the 120 and the 240 from different circuits. The rough-in is correct for this.

Problem is, the specs for the Leviton device say that it's good for 2HP, not 3.

What's a guy to do?

[Lavrans]

David- is there any reason you can't hardwire them in? Or a reason why you don't want to?

[David Meiland]

The floor box rough-in.... it's a big PVC hole in my slab. I suppose I could fab up a cover plate and run the wires from the machines thru it, using cable clamps. But then I can't unplug them easily. The shop is small. Ability to unplug and roll out of the way has to count for something.

http://www.hubbellpremisewiring.com/...E103F&pid=1218

The trim looks like this:

http://www.hubbellpremisewiring.com/...E103F&pid=1218

[jwelectric]

What kind of cord cap came with the table saw? This is the type of receptacle that it will require.

If a 120 volt circuit is going to be supplied from the same branch circuit then the conductors will have to be sized to carry both loads as well as having a neutral included with the circuit.

This is not going to be as easy as just plug and play.

[David Meiland]

The tablesaw has a factory, molded cord cap... straight blades, a ground plus two horizontal. When my electrician hooked this saw up at the jobsite he installed one of these:

http://www.leviton.com/OA_HTML/ibeCC...&section=10935

He installed it in the future location of the water heater connection, and downsized the breaker to 20A. Saw works great.

Tomorrow morning I will talk to the same electrician and get him to hook this up, but for now I am wondering if I can use the trim I have and get both machines connected to it.

The j-box that feeds the floor box has two circuits in it, one is 12/2 and the other is 10/3. I am assuming he can use the 10/3 wire to supply 20A 240V circuit for the saw (breaker = 20A, wire is oversized), and the 12/2 wire to supply 20A 120V for the dust collector.

Maybe what you are saying is that these receptacles are intended to be fed by one breaker.

[sparkyinak]

Dave, what is the actual NEMA cofig. for 240 cord? What type of saw is it going to be plugged in? Where are you getting the 3 HP? Could it possibly be 2+1 HP (saw + collector)? The description you gave on the 240 plug was a 20 amp, 240. If it is indeed a factory 20amp/240 volt config., then I would look in the owner's manual and see what is going on. If it turns out that it is a 2hp saw + 1 hp dust collecter then try this:

http://www.leviton.com/OA_HTML/ibeCC...&section=10928

If the cord supplied is a 20a/240v, the the recept has to be a 20 amps and the breaker has 20 amps. That's code. If the owners manual states to use 20 amp /240 recept then use a 20. More then likely the saw is a DIY saw so the duty cycle is limited. It is not considered to be hardwired to the building so the NEC does not apply to the saw, just the outlet. Portable equipment protection through proper use of the end user is resposible for the manufacturer. If addition protectional is required, it should state in the owners's manual. It may appear cheesy but if you follow the OM and the end user follows the OM, then in theory everything will work just fine.

[David Meiland]

Spark, the saw is a Delta Unisaw, sold as a 3HP. The cord cap is factory and would fit in the top half of the receptacle in your link. The dust collector is a separate item from a different manufacturer, and it's a 1-1/2 HP. It has a household plug, which could of course go in the bottom half of the receptacle.

[PaliBob]

Problem is, the specs for the Leviton device say that it's good for 2HP, not 3.

What's a guy to do?

The problem is that the tool manufacturers or sellers lie when it comes to HP.
Here is a review for a 6 HP tool: http://www.epinions.com/review/Craft...39988D89-prod3

Imagine asking Leviton for a 6 HP connector. OK that's a ridiculous example, but the point is that tool manufacturers do stretch claims on HP. The good news is that NEMA is held to a much higher standard. I believe the ratings by Leviton and the electric motor manufacturers much more than the tool merchandisers.

Now when it comes to Delta we don't know the real number unless we could clamp an ammeter on one of the legs and compute the Hp since a 3Hp motor uses 2.4KW. Another thing to do would be to check the motor nameplate. IMO a Delta 3HP saw would be much more likely be in the 2 HP range.

My reasoning on making this assumption is that NEMA motor manufacturers are believable when they say that 3 HP motors are larger and more expensive than used in a Unisaw. Here is a link to a Baldor "General Purpose" 3HP motor. Note the weight and the cost:
http://www.baldor.com/products/detai...g=40CMB%2DCONT

[PaliBob]

Duplicate of #8

[dgbldr]

David,

PaliBob is mostly right. Check the plate on the saw motor. If it says 20A or less, you're fine. What Delta and Leviton call horsepower are two different things.

Read this:http://ecmweb.com/mag/electric_under...duction_motor/

Also look at this:http://www.electricmotorwarehouse.co...sor_motors.htm

and notice they sell 2hp and 3hp motors, both of which have the same amp ratings. They also sell 2 different "5hp" motors, one takes 15A and one takes over 20A.

Leviton horsepower is an electrical rating, like watts consumed divided by 746. They don't know what you'll plug in. Motor horsepower (when rated honestly) is the mechanical output of the motor, calculated from the actual measured torque at rated speed. And derated according to the service class, etc.

dg

[dgbldr]

Now when it comes to Delta we don't know the real number unless we could clamp an ammeter on one of the legs and compute the Hp since a 3Hp motor uses 2.4KW. Another thing to do would be to check the motor nameplate. IMO a Delta 3HP saw would be much more likely be in the 2 HP range.

No Bob, not true. Read the first link in my post above.

The hp rating on a motor nameplate is NOT an electrical rating, i.e. is NOT the input power. It is the OUTPUT of the motor, calculated from the output torque at rated speed.

dg

[BillHartmann]

The over rating of motors is limited to universal motors that are built into equipment and induction motors on air compressors.

The motor used on aircompressor might be a a brand name, but will be marked Spl for the HP rating on the nameplate. And the compressor manufacture will put a different Hp number on air compressor body.

I believe that they are getting aways from that on the air compressors and going to NEMA ratings.

Apparently none of you know what a Unisaw is. It has a industrial case of table saw, often used in cabinet shops.

And use it will have a TRUE NEMA rate 3 ph (or optional 5 ph) induction motor.

Because of the special mount they aren't a standard NEMA sized motor.

This is on replacement motor from Leason.

http://www.amazon.com/3450RPM-Unisaw...5174870&sr=1-4
And Baldor also makes one. I think that the are the OEM, but not sure.

http://www.buyzillion.com/B0000223WG...hase+3450.html

Unisaw's run from $1500-1700 depending on the fence.

http://woodworker.com/cgi-bin/FULLPR...ARTNUM=961-409

This is a common "problem" in woodworking equipment. The equipment is not UL listed.

They will use listed motors, listed cordset, etc. But the equipment is not listed.

My Jet contractors saw, 1.5 hp 18/9 (115/230) comes setup wired for 120 and with a 5-15P.

[dgbldr]

And use it will have a TRUE NEMA rate 3 ph (or optional 5 ph) induction motor.

Bill, I vaguely remember hearing about 3 phase motors, but never anything about 5 phase... :)

dg

[PaliBob]

dg, Of course you're right on the power. I don't know where my head was. I know better than that. On my Baldor example http://www.baldor.com/products/detai...g=40CMB%2DCONT
The maximum efficiency of this real 3HP motor is 87%, and less at lower loads.

As regards to the OP question of whether or not the Leviton 5842 can be used on the 3HP Unisaw. IMO this will work because the motor load at startup only has to spin the blade. This won't be the same stress on the 5842 contacts as switching a fully loaded motor on and off.

On my 3HP motor example Link when I click on "Performance Data" and look at the "Load Characteristics", it shows 'Line Amperes' proportional to % of rated load. This is a more benign environment for the 5842 then switching on and off a fully loaded motor.