Can I make a switchable 120/240 outlet?

[Wow]

I have a twist-lock outlet on the ceiling in my shop. It was originally wired for 240v/30A with 2 hot wires and a ground, but no neutral. I wanted to tap 120v out of this outlet, so I moved one of the hot wires from the breaker to the neutral bus in the breaker panel.

That works fine, except if I want 240v again I have to go move the wire. I wonder if I could set up some kind of switch that I could just flip to change it from 120 to 240 volts and back? I know I *could* technically, but rather is there a safe, up to code way to do it? I saw a 30A double pole Square D "enclosed safety switch" switch for $13 at Lowes, might I be able to use that? I guess what I need is a "double pole, double throw" switch?

Running an extra neutral wire is out of the question, it would be way too difficult to run in my shop. I'll just switch it "manually" before I do that.

 

[mrb]

theres no good way to do what you want, and have it safe and legal. I went through a few different scenarios of possible ways to do it and nothing comes out good. The biggest problem is having 120v on a 240v receptacle or 240v on a 120v receptacle.

I did come up with one way to do it, but it would be so complicated and expensive you would just go buy an extension cord or even run a new circuit.

 

[nate379]

240v on a 120v style plug is fairly common where I grew up. Lots of farm stuff would use it.

The only difference was that the outlet was red.

And yes, if you are wondering, I have mistakenly plugged 120v stuff into them.

 

[mrb]

240v on a 120v style plug is fairly common where I grew up. Lots of farm stuff would use it.

The only difference was that the outlet was red.

And yes, if you are wondering, I have mistakenly plugged 120v stuff into them.

they used to make a receptacle (i forget what it was called) with two T slots in it which would accept all four combinations of 15a and 20a 120v and 240v plugs. Dont make those any more.......


I was thinking, if you absolutely HAD to do it, you could use a multipole cam switch to handle reconfiguring the connections and trigger a pair of LV coil contactors located up at the ceiling (where you have a 240v and a 120v receptacle) which would switch the proper receptacle in or out. It would be pretty expensive to do, and at that point you would just go run a new circuit, or buy an extension cord.

 

[Ray-CA]

My knowledge of electrical goes just a little beyond "on/off" but couldn't you pull a 120 circuit off the 240 and run that to a separate box installed near the existing box in the ceiling?

Ray

 

[mrb]

My knowledge of electrical goes just a little beyond "on/off" but couldn't you pull a 120 circuit off the 240 and run that to a separate box installed near the existing box in the ceiling?

Ray

no, because he has no neutral conductor in his 240 circuit.

 

[Wow]

My knowledge of electrical goes just a little beyond "on/off" but couldn't you pull a 120 circuit off the 240 and run that to a separate box installed near the existing box in the ceiling?

Ray

Yeah, I wish I could do that, unfortunately I'm 1 wire short.

 

[Charles (in GA)]

Run four wires, then install a 4 prong twist lock RV receptacle up there. Then make up a couple of adapter cords that have a male 4 prong twist lock on them, one where you pick up a hot and a neutral and a ground, and put a female end, 120v (as on a extension cord) on the other end. Make another cord also with the twist lock and pick up the two hots and the ground and put a female 240v end on it. With both adapter cords you get what you need without the risk of you or anyone else switching to the wrong voltage and burning up something.

Charles

 

[Wow]

Run four wires, then install a 4 prong twist lock RV receptacle up there. Then make up a couple of adapter cords that have a male 4 prong twist lock on them, one where you pick up a hot and a neutral and a ground, and put a female end, 120v (as on a extension cord) on the other end. Make another cord also with the twist lock and pick up the two hots and the ground and put a female 240v end on it. With both adapter cords you get what you need without the risk of you or anyone else switching to the wrong voltage and burning up something.

Yeah, that would be great, but I think you missed the point of my post. I think I am smart enough to keep a switch at the right voltage, were I able to come up with one...

 

[mrb]

Yeah, that would be great, but I think you missed the point of my post. I think I am smart enough to keep a switch at the right voltage, were I able to come up with one...

yeah, but you said you want it safe and up to code....for this you need 4 wires.

 

[Sokoloff]

+1 on mrb's answer, at which point you might as well just run a whole separate circuit so you could have an L6 twist-lock for 240 and an L5 for the 120.

 

[mrb]

another thing worth noting: if you have a contraption wired up like that, and the insurance investigators find it in the smoking remains of your home/garage (whether it caused the fire is irrelevant here), good luck getting them to pay the claim.

 

[APEowner]

It's neither safe nor up to code but all you really need is a single pole double throw switch that selects either the neutral buss or the power from the breaker and connects it to the wire just like you're doing manually.

However, I really think this is a bad idea.

The only safe way to do this with the wires you have would be to have a device at the outlet end that applied power to the correct terminals of a multi-pole socket based on the voltage across the two wires but by the time you did this you could probably have someone run another wire.

If you really need both outlets there I'd look at running surface mount conduit.

 

[mrb]

It's neither safe nor up to code but all you really need is a single pole double throw switch that selects either the neutral buss or the power from the breaker and connects it to the wire just like you're doing manually.

However, I really think this is a bad idea.

The only safe way to do this with the wires you have would be to have a device at the outlet end that applied power to the correct terminals of a multi-pole socket based on the voltage across the two wires but by the time you did this you could probably have someone run another wire.

If you really need both outlets there I'd look at running surface mount conduit.

you couldnt have a 4 wire receptacle, because it would have no neutral when in 240v mode. You would have to have two 3 wire receptacles. You could have a pair of contactors to switch the outlets in and out which are controlled by a multipole cam switch at the supply end which also switches the power conductors, but by the time this is over with you could have run several new circuits.

 

[Aceman]

So, bottom line is:

1. Run another circuit.
2. Run an extension cord.
3. Keep swapping wires back and forth.