Can you wire a second 240V receptacle into an existing 240V circuit?

[DJJ]

Or do these have to be dedicated, one-receptacle circuits?

[Nitrogen]

What existing deviceis there?  What amperage doesit pull?
And what amperage will your new device pull?   Make sure the combined pull is handleable by the wiring and circuit breaker.

Oh, and check your wiring code.

[Matthew Carberry]

The wiring code is a scam created by the guvmint to prevent you from exercising your freedom to stupidly burn your house down accidentally.

See, they have an investment in your home, if it burns, the property tax revenue will drop AND they'll have to actually provide the fire and rescue services you pay for.

As long as they can dictate that you build safely, the house will maintain or increase in value, taxes will continue to be paid and they won't have to put any wear and tear on their shiny fire trucks.

So stick it to the man, ignore the code. 

(or do what Nitro recommends)

[geronimotwo]

i'm not sure if code allows it, but it shouldn't be a problem functionality speaking. as long as both outlets and all wire can handle the current of the breaker (never put in a higher rated breaker), the worst that will happen is the breaker will trip when both outlets are used simultaneously. unless the breaker malfuntions, in which case you will have that drastic reduction in property taxes.

what do you plan on using the outlets for?

[Firethorn]

what do you plan on using the outlets for?

As others have noted, this is the critical question.  In the USA, a 240V receptacle is normally only installed for high wattage applications where a 120V circuit is no longer practical.  You can push almost twice as many watts over a given cable gauge at 240V, after all.

So, normally speaking, whenever you see a 240V circuit it was designed and installed for a particular application, and the wiring sized for it.  Thus, unless for some strange reason they oversized the circuit or you can guarantee that both appliances aren't going to be used at the same time, you'll probably end up running a new circuit.

For example, an electric water heater is normally set up for 30 amps - because in normal use it takes around 25.  Same with an electric dryer.  Both shouldn't exist on the same circuit unless you like breakers popping or you have some way to make sure the water heater and dryer don't operate simultaneously.

[ilbob]

Or do these have to be dedicated, one-receptacle circuits?

I do not recall that the code imposes a limit.

[280plus]

As long as the combined amp ratings of the receptacles does not exceed the main circuit branch, you are ok.

[Firethorn]

As long as the combined amp ratings of the receptacles does not exceed the main circuit branch, you are ok.

Actually, you can exceed the amp ratings of the main circuit branch, this is frequently done with 120V wall outlets, remember.  Each outlet is rated at 15 or 20A, and you got loads of them.  It's just that it's not anticipated that most will be used, or even used near their capacity.

[ilbob]

As long as the combined amp ratings of the receptacles does not exceed the main circuit branch, you are ok.

this is not even an issue.

[DJJ]

Well, I've heard from other sources that it's a flat-out no, so it's back to the drawing board.

[Matthew Carberry]

Well, I've heard from other sources that it's a flat-out no, so it's back to the drawing board.

Other sources? 

OTHER sources?

Why the heck are you going outside APS for advice?

The only reasonable explanation is that you think we don't know what we're talking about. 

 

[280plus]

As long as the combined amp ratings of the receptacles does not exceed the main circuit branch, you are ok.

this is not even an issue.

It is if you try to run both at capacity at the same time.

[ilbob]

As long as the combined amp ratings of the receptacles does not exceed the main circuit branch, you are ok.

this is not even an issue.

It is if you try to run both at capacity at the same time.

no more than if you plugged in two hair dryers into the same outlet and turned them both on. the only negative thing that will happen is that the breaker will trip.

The OP asked if they had to be dedicated circuits. The rating of an outlet or the combined ratings of all the outlets on the circuit just is not an issue to that question.

There are a few cases where the code requires dedicated receptacles IIRC. I think electric ranges are one.

[280plus]

The OP asked if they had to be dedicated circuits. The rating of an outlet or the combined ratings of all the outlets on the circuit just is not an issue to that question.

Ohhhh,,,gotcha! 

[never_retreat]

I depends on you application.
If this is for non fixed in place loads (ie portable something) you can draw up to 80 percent of the over current device. If it is for a fixed in place load you can only draw 50 percent of the over current device(range with a cord). Although you have to abide by what the manufacture of the device lists for the over current device size, not the electric code. The amperage listing on a UL approved piece of equipment trumps the NEC.
Since i don't know what your trying to connect I'll give a short run down.
Two 240v 20A outlets in your workshop for tools OK
Connecting an ac unit to your electric dryer NO
Connecting the dryer to a range NO
Under certain circumstances you can connect a cook top and wall oven together.

[DJJ]

Someday I'm planning on building a "doghouse" behind my garage for a dust collector and an air compressor. The dust collector would be on the 240V circuit. I've had the circuits installed. However, they're on the exterior wall, so they do me no good now. For now, I need a portable dust collector until I get the doghouse built. I can wire another receptacle (probably in the garage ceiling) into the circuit that goes to the one outside in just a few minutes. This ultimately means that there would only ever be one device on the circuit. Who knows? If the portable dust collector turns out to be adequate, I may never build the doghouse.

[Gewehr98]

240v 9-ft South Bend lathe in garage, tied to 240v clothes dryer outlet on other side of garage wall? 

(Not saying I have or haven't done this...)

[ilbob]

I depends on you application.
If this is for non fixed in place loads (ie portable something) you can draw up to 80 percent of the over current device. If it is for a fixed in place load you can only draw 50 percent of the over current device(range with a cord). Although you have to abide by what the manufacture of the device lists for the over current device size, not the electric code. The amperage listing on a UL approved piece of equipment trumps the NEC.
Since i don't know what your trying to connect I'll give a short run down.
Two 240v 20A outlets in your workshop for tools OK
Connecting an ac unit to your electric dryer NO
Connecting the dryer to a range NO
Under certain circumstances you can connect a cook top and wall oven together.

I am not sure where the numbers you quoted came from but they are just plain wrong.

Cord and plug connected loads are not part of the premises wiring so they are not covered by the NEC.

UL listing of a piece of equipment never trumps the NEC. In fact, it is extremely rare that the NEC has anything to do with a UL listing at all. The code does require that you follow the installation instructions that come with a listed device, but in no way is that "trumping" anything.

[geronimotwo]

another thought is to make a 220 extension cord. get some wire of appropriate size, a plug and outlet of the right type, and you can put it wherever you like. no need to splice into the existing line.

[Tallpine]

I don't see any problem unless both devices will be in use at the same time.

Even then, it will only be a nuisance to trip the breaker - though keep in mind that breakers will eventually wear out if tripped too often.   And we used to have an old house that you couldn't buy replacement breakers for except at an extremely high price, as the company was out of business.

[Matthew Carberry]

I don't see any problem unless both devices will be in use at the same time.

Even then, it will only be a nuisance to trip the breaker - though keep in mind that breakers will eventually wear out if tripped too often.   And we used to have an old house that you couldn't buy replacement breakers for except at an extremely high price, as the company was out of business.

Putting in a new panel is fun though.

[Firethorn]

Putting in a new panel is fun though.

Been there, done that, wasn't too difficult.

The biggest fun I had was working with the live, unfused(until the power pole), utility line.  I wrapped them up good before moving them.

[Matthew Carberry]

You didn't have a exterior meter with a shut off? 

[Firethorn]

You didn't have a exterior meter with a shut off? 

What can I say...  It's legacy.

It's an old 60 amp service.  If the power company shuts it off I'll have to update it before they'd turn it back on.  Don't have the money for that at the moment.

When I started the house had a main fuse box, 2 sub fuse boxes, and a circuit breaker box.

One day I was having some wierd power issues, went down to the basement and found the main fuse box sparking.  I had already obtained a new breaker box, just moved up my replacement plans by quite a bit.  I replaced the other two fuse boxes with utility ones to extend the wires to the breaker box.

So I still have a 60 amp service, but at least it's all new breakers.

[Matthew Carberry]

I don't get all freaked out by working near hot leads anymore (if I have to) but I don't know I'd want to try to unhook a main power cable.

What did you wrap it with?