[nomad943]

Here is my situation.
We are wiring in a new install AC compressor and have extremely limited space in our circuit panel.
Basicaly all the circuits are used ... period.
However, as luck has it, the wire that goes to our seldom used clothes dryer runs directly past the location where the compressor will be located.
So here is the idea; Put in a switch that will allow us to operate one or the other but not both at the same time.
This way the wiring and the breaker will stay well in spec and we will be wanting to use both the dryer and the ac at the same time about never anyhow.
I hear that such switches do exist but I can find no such thing.
What would such a nice safe UL rated (220v-40A) switch be called and where would I find one? Any ideas?

 

[InPhase277]

I personally don't recommend it. You have already spent some cash on the new A/C, may as well fork over a little more for a new circuit.

But if you did do it, why even bother with a switch since both appliances are controllable? I mean, the dryer comes on when you turn it on, and so does the A/C. There is no chance of either coming on automatically by accident. Also, the dryer circuit is likely 30 A, and if it is old enough, may not have a ground in the circuit.

 

[nomad943]

Accidents do happen and controlable or not, someone could still flip on the dryer while the compressor was running. This event likely would melt the #10 copper wire that feeds it should the breaker be slow and who knows ... I dont like to gamble.
The circuit is fairly new and it is 30 amps which is plenty to power the compressor (it needs 20),
I know that the right answer is to strip out the wire and run up a bigger bill putting in a mile of #8 and a new drop down but ...
I'm trying to save a few bucks and stay safe.

 

[InPhase277]

Well then, I'll leave to others to lay out the details, 'cause I'm heading out the door. But I will say that you will need to fuse the A/C at 20 A. And, with a little creativity, and a 30 A DPDT relay with a 24 V coil, you could make it automatic. When the A/C kicks on, it breaks the circuit to the dryer. That would be cheap and convenient.

But for the record, I still say run another circuit...

 

[joed]

Why do you need #8. A 20 amp circuit only needs #12. Dryer needs #10 for 30 amps. This is a very bad idea made worse by the fact that the two units don't use the same size OCPD.
A sub panel is your solution.

 

[nomad943]

Why do you need #8. A 20 amp circuit only needs #12. Dryer needs #10 for 30 amps. This is a very bad idea made worse by the fact that the two units don't use the same size OCPD.
A sub panel is your solution.

The combined current (30 plus 20) would force me to use #8 as the run is way over 50 feet.

 

[nomad943]

Well then, I'll leave to others to lay out the details, 'cause I'm heading out the door. But I will say that you will need to fuse the A/C at 20 A. And, with a little creativity, and a 30 A DPDT relay with a 24 V coil, you could make it automatic. When the A/C kicks on, it breaks the circuit to the dryer. That would be cheap and convenient.

But for the record, I still say run another circuit...

Hmm .. I was thinking more along the lines of rigging a double throw or using some kind of transfer switch but your idea sounds VERY interesting. I will have to dig around for some literature on those things and see if it would be practical

 

[Yoyizit]

or using some kind of transfer switch

IMO, a 30A DPDT relay rated for motor loads is way easier to get than a xfer switch at this rating.

Or, if you don't mind digging into the HVAC 'stat you could run a low voltage relay and a current sensing switch that senses dryer current draw and prevents HVAC operation.
Or, you could dig into the 'stat and the dryer gizzards so you wouldn't need the current sense switch.
Either method is probably cheaper but somewhat trickier.

 

[hayewe farm]

As long as you use the same size wiring to the compressor as to the dryer, why not just install a dryer cord to a box connected to the compressor wires. Unplug the dryer and plug in the compressor, unplug the compressor and plug in the dryer as needed. It's not the way I would do it but it would work. Be aware the dryer probably has two hots and a neautral and should have a ground and the compressor probably only uses the two hots and a ground.

 

[ScottR]

When the A/C kicks on, it breaks the circuit to the dryer. That would be cheap and convenient.

.. Except when it shuts off the dryer with a wet load in it.. :wink:

If it's listed for it you could put a tandem breaker in your panel and just run #12 for the A/C.. (They have double-pole tandems in 30A/20A combinations for 240V applications).

Just to play devil's advocate: You're running back-to-back loads one day in the dog days of August. Your dryer is running for 2-3 hours straight. Do you really want the A/C off for that long?? And if you forget to flip that DPDT back to A/C mode, you probably won't remember it until you're already sweating. :whistling2:

 

[Speedy Petey]

No way I'd use a DPDT switch or any sort of shared circuit for this.

Run a new line as the others have stated. Use twin/tandem breakers or install a small sub-panel and move some circuits over to that to make room.

What you are proposing is a complete hack job and not worth the effort you will be putting into it.

Also, your thinking is not correct that 20 plus 30 equals 50. It's not that simple. Besides, you cannot do it that way. If you did you would HAVE to install a sub-panel anyway.

Do this right thing, install a sub-panel. Better yet, get a service upgrade with a larger panel.:thumbsup: