Using a DP switch for 120v?

[Wade Lippman]

I just bought a Grizzly H8243 switch for use on a router table. It says 20a/250v and 35a/125v. I presume that is achieved by wiring the 120v to both poles, so there is only 17.5a on each. Does that sound right?

I have an email into Grizzly, but I expect them to tell me to consult an electrician for the proper use of switches.

[Chris Padilla]

Hmmm, should I lock this thread before it gets out of hand, Wade? :p

;)

[Art Mann]

The rating on the switch has to do with how much current it can interrupt, not whether both poles are wired in parallel. If you want to use both poles, you can certainly wire it that way, but it isn't necessary. You can also wire it to switch both the hot wire and the neutral wire. I'm not sure what that would accomplish, but it wouldn't hurt anything. Also, you can just switch the router with one of the poles and ignore the other one. Whatever suits your fancy.

[Wade Lippman]

The rating on the switch has to do with how much current it can interrupt, not whether both poles are wired in parallel. If you want to use both poles, you can certainly wire it that way, but it isn't necessary. You can also wire it to switch both the hot wire and the neutral wire. I'm not sure what that would accomplish, but it wouldn't hurt anything. Also, you can just switch the router with one of the poles and ignore the other one. Whatever suits your fancy.

My reasoning is that if each pole can handle 20a (when used as a DP for 240v) to get it to handle 35a on 120v you would HAVE to use both poles. If a single pole can't handle more than 20a on 240v, it shouldn't be able to handle more than 20a on 120v.

Grizzly replied saying I should put one line wire on each pole. I reminded them I asked about 120v so there is only one line wire,

[Art Mann]

Your reasoning is quite reasonable. It simply isn't correct. What it means is, the higher the voltage, the less current the switch is able to interrupt. If it makes you feel more confident, by all means, wire the two poles in parallel. It wont hurt a thing. However, that is not what is implied by lower current ratings at higher voltages. The ratings on single pole switches are also higher at lower voltages.

[Randy Klein]

Your reasoning is quite reasonable. It simply isn't correct.

Art, if you don't make that your new signature, I just may have to steal it...:)

[Matt Meiser]

Grizzly replied saying I should put one line wire on each pole. I reminded them I asked about 120v so there is only one line wire,

True, but the 110V stationary tools I've messed with electrically have usually switched both the line and neutral.

[Tom Veatch]

True, but the 110V stationary tools I've messed with electrically have usually switched both the line and neutral.


Just curious. Would those tools possibly have had dual voltage motors that could be coverted to 220V by reconnecting a couple of wires in the junction box?

If so, it would make sense to switch both leads to cover the 220V case even though it's not functionally required even in the 220V case.

[Jim O'Dell]

My TS was wired with the hot and neutral both being switched. When I changed it to 220 last year, of course both hots get switched and the ground is, well a ground.:rolleyes: Wiring both hot and neutral will not add more amp capacity to the 110.
Another thing you could do with a switch like this wired for 110, is let another power line go throught the switch to control a vacuum cleaner or a light. Lots of possibilities. Would be really good for a drill press to control a goose neck light! Jim.

[Wade Lippman]

Your reasoning is quite reasonable. It simply isn't correct. What it means is, the higher the voltage, the less current the switch is able to interrupt. If it makes you feel more confident, by all means, wire the two poles in parallel. It wont hurt a thing. However, that is not what is implied by lower current ratings at higher voltages. The ratings on single pole switches are also higher at lower voltages.

You are essentially saying that the capacity of a switch is measured in watts, rather than amps. Is that correct?

But you are also saying that it doesn't matter whether you use one pole or two, the power capacity is the same. (It can handle 20a/240v, 4800w on two poles; or 35a/120v, 4200w on one pole.)

You might be right, but I would think (perhaps incorrectly) that two poles would have significantly greater capacity than one.

[Rick Christopherson]

You might be right, but I would think (perhaps incorrectly) that two poles would have significantly greater capacity than one.No, it doesn't matter if you break one pole or two, the interruption in the circuit is the same.

Contrary to what many people think, a 240 volt circuit does not have half the current flowing in one pole and the other half flowing in the other pole. Regardless whether it is 120 volt or 240 volt, a circuit requires both conductors, and the exact same current is flowing through both wire, regardless what we call them. The neutral and hot wires are both current carrying conductors, the only difference is that the neutral is referenced to ground.

Consider a Hollywood movie. You've seen videos where a camera was mounted to the fender of a car looking past the wheel. From this camera angle, you can see the wheel bounce up and down with each bump in the road. The road looks rough and the wheel is moving relative to the car frame. There have also been camera angles where the camera was attached to the wheel. In this case, you see the road as being steady, but the car bounces up and down. So which is moving relative to the other, the car or the wheel? It is all a matter of where your perspective is from. For the U.S. electrical system, consider this to be the same as having a camera mounted to the neutral wire. Just because the neutral wire is not changing with respect to our reference point does not mean it is anything different from the other wire in the circuit. It just means that we have anchored this wire to a specific reference point.

[Wade Lippman]

Your reasoning is quite reasonable. It simply isn't correct. What it means is, the higher the voltage, the less current the switch is able to interrupt. If it makes you feel more confident, by all means, wire the two poles in parallel. It wont hurt a thing. However, that is not what is implied by lower current ratings at higher voltages. The ratings on single pole switches are also higher at lower voltages.

After reading your reply I posted a similar question elsewhere. Someone there explained why you are correct. Since the two poles are unlikely to open precisely simultaneously, one will ocassionaly actually see 240v; hence the 240v rating is lower.

My theory is bad for the same reason; since the two pole will not necessarily open at the same time, two have no more 120v capacity than one. At least not reliably.

[Matt Meiser]

Just curious. Would those tools possibly have had dual voltage motors that could be coverted to 220V by reconnecting a couple of wires in the junction box?

Most yes, but I had a drill press that had a 110V only wire that was wired this way. My point was just that that was what Grizzly was probably refering to.