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Old 07-26-2014, 02:26 PM   #1
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220v relay


So I have an application which uses a 220v relay switch, with a 220v coil. The only thing I need to confirm, is that the coil has two contacts. Normally, when I use a 110v coil, it's obvious that you use the line and neutral wires (black and white wires) to power the coil. With the 220v coil, are you using the 2 line wires (red and black in my situation)? I'm thinking you must since if you used one hot wire, and the neutral, you only have the 110v.
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Old 07-26-2014, 03:11 PM   #2
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You are correct. The alternating phases are what make 240v out of 2- 120v lines.


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Old 07-26-2014, 04:05 PM   #3
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See those 3 wires coming to your house?

2 Of them are 120Vac each....180 deg out of phase. The other is neutral.

Neut to either wire gives you 120Vac....but hot to hot...240Vac...

With that said.....it's Saturday....it's hot....It's beer time....
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Old 08-02-2014, 08:24 PM   #4
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So, another related question. For the same 220v relay, if I wanted to cut power to the relay, can I put a switch in one of the hot coil legs? If I do that, is it ok for the switch to be rated for 20a 125v since it's only one leg?
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Old 08-02-2014, 08:26 PM   #5
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Quote:
Originally Posted by taylorjm
So, another related question. For the same 220v relay, if I wanted to cut power to the relay, can I put a switch in one of the hot coil legs? If I do that, is it ok for the switch to be rated for 20a 125v since it's only one leg?
No, it needs to be rated for 240 vac.
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Old 08-02-2014, 08:40 PM   #6
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Ok. Not that I'm doubting you, but only because I like to learn. So, since the switch is only interrupting one hot leg, it's not switching a neutral, or the other hot, how does the switch know it's 240v?

Actually, now that I looked at it, the switch I was going to use is rated at 20a 125v or 15a 250v. I would have though the amps would have been cut in half for the 250v. Does that sound ok?

Last edited by taylorjm; 08-02-2014 at 08:48 PM.
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Old 08-02-2014, 10:21 PM   #7
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Quote:
Originally Posted by taylorjm View Post
So, another related question. For the same 220v relay, if I wanted to cut power to the relay, can I put a switch in one of the hot coil legs? If I do that, is it ok for the switch to be rated for 20a 125v since it's only one leg?
It would work, as breaking one leg breaks the circuit; but its not okay. When you turn the switch off there will still be 120v at the relay. Everyone, probably including you, will think it is dead and will be unpleasantly surprised.

Think of it as putting the switch on the 120v neutral instead of on the hot; it works, but is not safe.

To answer your second question; a 240v switch is across both legs.
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Old 08-03-2014, 06:25 AM   #8
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Quote:
Originally Posted by Toller
It would work, as breaking one leg breaks the circuit; but its not okay. When you turn the switch off there will still be 120v at the relay. Everyone, probably including you, will think it is dead and will be unpleasantly surprised. Think of it as putting the switch on the 120v neutral instead of on the hot; it works, but is not safe. To answer your second question; a 240v switch is across both legs.
A controller does not have to break both legs, but the disconnect does.
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Old 08-03-2014, 06:29 PM   #9
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So is a relay considered a controller?
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Old 08-04-2014, 12:20 PM   #10
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Quote:
Originally Posted by taylorjm View Post
Ok. Not that I'm doubting you, but only because I like to learn. So, since the switch is only interrupting one hot leg, it's not switching a neutral, or the other hot, how does the switch know it's 240v?
The voltage across the switch is 240V when it's open. You are not switching "one" hot leg, you are opening a 240V circuit.
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Old 08-04-2014, 02:31 PM   #11
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After thinking about it some more, I see what you mean. Once the circuit is complete, there is 240 running through that single wire I was going to cut, so the switch would need to be rated to handle that load.
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