can a two prong variac be converted to a three prong variac?

[jeremy]

i have an old variac thats two prong. i tested it with a meter and it seems to work fine. is there a way to convert it to three prong? i mean, i know i can buy a three prong cord and outlet, but im unsure if theres something im not aware of.

 

[Artie]

Sure. The 3rd prong of the plug is connected to the neutral prong back at the breaker box. Just connect the 3rd prong of your new input cord to the 3rd prong of the new outlet. There would be no connection to your variac itself. Just make sure to reorient neutral-to-neutral and line-to-line on the new cable and outlet.

But ask an electrician.

 

[jeremy]

ok, thats what i thought. just wanted to make sure i wasnt over simplifying things

 

[Artie]

If your house burns to the ground, I disavow any knowledge of this conversation.

P.S. Why do you want to do this?

 

[ehdwuld]

Oh he's talking about changing the cord on the variac
not the receptacle on the wall

connect the hot and neutral (black and white respectively) in the same places as the two wire existing cord
connect the green to the metal chassis

 

[ErikH]

Oh he's talking about changing the cord on the variac
not the receptacle on the wall

connect the hot and neutral (black and white respectively) in the same places as the two wire existing cord
connect the green to the metal chassis

Yeah. That’s what I was thinking. Same as changing an old 2 prong amp to 3. Center pin goes to chassis. The outlet ground pin goes to ground per code.

 

[jeremy]

right, thats what im thinking. the ground is isolated from the actual coil of the variac, its just a ground wire.

i cant imagine itll burn anything down. i can start at zero volts

 

[Artie]

Oh he's talking about changing the cord on the variac, not the receptacle on the wall.

I get that. But the variac itself has a receptacle. I meant 3rd prong, wire-to-wire on the variac cord-to-receptacle. It would mean also replacing the receptacle on the variac.

At least, I thought that's what he meant.

 

[jeremy]

it is what i meant, yes. thanks!

 

[ehdwuld]

Oh oh

I feel stunned

Never crossed my mind that the variac had a receptacle

 

[ErikH]

I didn't realize that either.

 

[jeremy]

theres a cord to plug into the wall outlet, then an outlet (receptacle) where you plug in whatever youre wanting to control the voltage to, and a dial to bring the outlet from 0v-130v

 

[ErikH]

Ohhhh, right. Otherwise, how else would it work. Duh! (silly me).

Well, that being said, I would think wiring it up to match what goes to the wall would be the ticket. That is, if you're converting the cord to the wall and the appliance receptacle at the same time. Receptacle ground pin to the cord ground pin so when it's plugged in to the wall, all 3 pins are connected as they should.

I would double-check with a few amp techs to verify that.

 

[jeremy]

it should be pretty simple, but i wanted to make sure i wasnt missing something before i fry myself

 

[ehdwuld]

Take pictures
post them
Get feedback before fry back

 

[jeremy]

i wouldnt actually fry. ive taken 120v plenty of times. enough that my body literally defies the orders from my brain to touch things once it has zapped me. its kinda comical. but i will document the process if people wanna see it

 

[Artie]

Yes . . . connect wire from red arrow, (new cord), to green arrow, (new internal receptacle).

 

[ehdwuld]

Yes . . . connect wire from red arrow, (new cord), to green arrow, (new internal receptacle).

Would you wire directly
or to a common lug on the housing

I assume you would have to create a common lug

I would want to ground the metal case as well

 

[jeremy]

yep, totally know what needs to go where. ill open it up when i have time and see what i have in there, then make a plan. i already formed the caps i needed, so theres less of a immediate need.

 

[Artie]

Would you wire directly
or to a common lug on the housing

I assume you would have to create a common lug

I would want to ground the metal case as well

The jury's still out on that. When whatever what electrical committee made these rules, 51% voted "yay", lets do 3-prong. 49% voted "nay" . . . It's stupid since the 3rd prong and neutral are shorted together back at the panel. (Their comment. Not mine.) Most diagrams keep it separate, on a variac. Connected, on most other equipment. That way, the connection is determined by what you plug into it.