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Thread: Wiring a switch for 110 volts

  1. #1
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    Wiring a switch for 110 volts

    OK I just received a new switch and was wondering if it a practice to switch both sides of the 110 volt circuit. I know it will work with the line side switched only but is there any reason to switch both the line and neutral?

  2. #2
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    Hardly an expert, but my understanding is that 110v doesn't need it, but it wouldn't hurt if you did. Of course, you'd need a dual pole switch - those aren't quite as common. They're used a lot in 220v applications, obviously, due to the two hot lines.
    Jason Beam
    Sacramento, CA

  3. #3
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    Charles, in the USA, the wiring convention is to switch 110/120v ungrounded (hot) conductors only - not the grounded (neutral) or grounding (equipment grounding) conductors.

    As Jason said, you could switch both leads - but would need a 2-pole switch to do that.

    Rob

  4. #4
    In some cases switching the neutral can be a bad idea depending on how the item is wired and used. If you are wiring a device with a plug and the device only has a two prong plug then switching the neutral can be a bad idea. It could under the correct settings lead to an unsafe condition.

  5. #5
    Charles - not sure what your electrical code may be for your area. But IMHO - breaking a ground any any case could be bad. I know you're talking about the neutral in your post - but back to the code comment - if your place is old enough or wired incorrectly, the neutral may be ran through the ground at some point.

    Cut the hot - let the neutral be a return path as it's intended.

    If for some strange reason the hot needs to "return" to the source and there's no where to go - it's anyone's guess where it might go. If it can't find ground - then you have the potential to become ground!
    Steve Beckham

    Epilog Mini 24 with 45 Watt, Ricoh GX 7000 Sublimation, Corel X3, Corel X4 and PhotoGrav, Recently replaced the two 'used' SWF machines with brand new Barudans.

  6. #6
    switch the hot (black) and neutral (white). If this is a tool that can be wired 120 or 240 then by switching both you won't have to rewire the switch if you rewire the motor. Also, by switching both hot and neutral you'll make sure that when the switch is off, power isn't going pass the switch if; someone screwed up and made the white hot and the black neutral, normal conditions where white and black are wired correctly, and the rare encounter with balanced 110AC where black and white are both hot (+60 on black, -60 on white, used in recording studio's to lower the noise floor).

  7. #7
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    Quote Originally Posted by Rob Russell View Post
    Charles, in the USA, the wiring convention is to switch 110/120v ungrounded (hot) conductors only - not the grounded (neutral) or grounding (equipment grounding) conductors.

    As Jason said, you could switch both leads - but would need a 2-pole switch to do that.

    Rob
    The switch is a 2-pole and the motor is wired for 110 at the moment.

  8. #8
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    Quote Originally Posted by Charles Wintle View Post
    The switch is a 2-pole and the motor is wired for 110 at the moment.
    I'd still only switch the hot leg. The only reason I can think of to switch both legs is so you can use the switch as a 'disconnect', for example to kill a table saw when you want to change blades. I believe it's safer to unplug a machine in those circumstances and have the plug sitting on top of the machine where you can see it while working on the machine.

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    Quote Originally Posted by Rob Russell View Post
    I'd still only switch the hot leg. The only reason I can think of to switch both legs is so you can use the switch as a 'disconnect', for example to kill a table saw when you want to change blades. I believe it's safer to unplug a machine in those circumstances and have the plug sitting on top of the machine where you can see it while working on the machine.
    Makes sense to only wire the hot leg of the circuit when using 110volts. I understand that both sides need to be switched when using 220volts.

  10. #10
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    Quote Originally Posted by Charles Wintle View Post
    Makes sense to only wire the hot leg of the circuit when using 110volts. I understand that both sides need to be switched when using 220volts.
    Actually, switching 1 leg of a 220/230/240v circuit will stop/start the device as effectively as switching both legs.

    If you don't want any power to the receptacle (or a hard-wired machine), you need to switch both legs on a 220/230/240v circuit.

    Rob

  11. Quote Originally Posted by Charles Wintle View Post
    OK I just received a new switch and was wondering if it a practice to switch both sides of the 110 volt circuit. I know it will work with the line side switched only but is there any reason to switch both the line and neutral?
    I am not sure how one switch would control both hot and neutral.


    However, my practice (and I believe Code) is to wire the switch so that it interrupts the hot wire.

  12. #12
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    Quote Originally Posted by Cliff Rohrabacher View Post
    I am not sure how one switch would control both hot and neutral.


    However, my practice (and I believe Code) is to wire the switch so that it interrupts the hot wire.
    Cliff,
    The switch is a 3PST type. I can be wired for 120vac, 220vac or 3 phase.

  13. #13
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    Quote Originally Posted by Rob Russell View Post
    Actually, switching 1 leg of a 220/230/240v circuit will stop/start the device as effectively as switching both legs.

    If you don't want any power to the receptacle (or a hard-wired machine), you need to switch both legs on a 220/230/240v circuit.

    Rob
    I understand that will cut power to the 240V equipment. But with the other leg "hot" and it's accidentally touched or connected to a ground or neutral, you'd still have 120V running through you right? Best to unplug I would think.

  14. #14
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    Quote Originally Posted by Russ Filtz View Post
    Best to unplug I would think.
    Yup. That's what I said too.

    I believe it's safer to unplug a machine in those circumstances and have the plug sitting on top of the machine where you can see it while working on the machine.

  15. #15
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    Quote Originally Posted by Steven Wilson View Post
    switch the hot (black) and neutral (white). If this is a tool that can be wired 120 or 240 then by switching both you won't have to rewire the switch if you rewire the motor. ...
    But, in that case, if the motor is rewired and the same circuit is used, the circuit is also going to have to be modified at the panel to move the white wire from the neutral bus to the other pole of the dual (240v) breaker. That means everything on that circuit will see 240 volts. Not a problem if there is only one outlet, except that the plug and receptacle will also need to be changed to one of the 240v configurations. With all that going on, inserting the 2nd pole of the switch into the newly hot white wire is not much added effort.

    I vote for leaving the neutal wire unbroken as long as it's a 120v circuit.
    Tom Veatch
    Wichita, KS
    USA

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