How do I know if I need a new switch for 240v?

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I have a Delta hybrid TS (36-715) and just wired it for 240v. Now the thing starts up so fast it makes me worry about belt wear.
Anyway, in the manual it says to make sure I have a 240v rated switch. The switch has no rating marked on it so how can I find out if it is ok?
-Steve
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A 240v switch opens both wires rather than just one. All my tools say if it is 240v in the manual; if yours warns you to be sure you have a 240v switch, you probably don't. If it doesn't say on the switch, you can tell by measuring (after the switch, with the switch on off) the voltage from each wire to ground. If either is 120v, then it is a 120v switch. That explains why you need a 240v switch. While the tool works fine either way; a 120v switch leaves wire energized that you would expect to be dead.
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Please don't give electrical advice.
There is a huge difference between whether a switch is physically capable of switching 240V (DPST), and whether the contacts (regardless of switch configuration) are rated at 240V.
Even a SPST switch is technically capable of switching a 240V device on and off--if any break occurs in the circuit (that is, either leg) the motor will not run. That is what you alluded to. There has been a fair amount of debate here as to whether that's a good idea or not.
However, if the switch contacts are only rated for 125V service it's not a good idea to employ the switch for 240V use irrespective of whether it's a SPST or DPST.
Now, to answer the OP's question, I would be very surprised if there wasn't any voltage rating marked on the switch. I would have thought that a requirement. In any event, I believe one of the other poster's answer is probably a good idea--contact Delta.
--
LRod

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You are FOS. A SPST is not a 240v switch in this country, even if it is rated for 240v. If you look at a SPST circuit breaker it says "120/240vac". By your reasoning you could use one to protect a 240v circuit. It would work, wouldn't it. Well except that the circuit would still be energized between the unswitch hot and the switch. There is no debate over it; well, except between you and another person FOS. A DPST is a 240v switch; find one on a woodworking machine that isn't rated for 240v. There is no reason to read the switch, except to see if it opens both wires.
In fact, a motor switch will handle a larger motor on 240v than on 120v; didn't you know that?
In short, open both wires good, open one wire bad.
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Take a look at some of the new contactors being used to switch air conditioning compressors on/off. Some of the new ones only have ONE contact point, yet they switch 240 VAC on/off all the time. Personally, I don't like it but it works because current only flows when the two legs form a circuit. Interrupt either one and you break the circuit. The same thing would happen if you put a SPST in one of the 240 VAC legs. I certainly wouldn't suggest that, but it'd work -- for how long I don't know as the switch contacts might not handle the current load for very long. My suggestion -- CONTACT DELTA and don't give up until you talk to someone you trust!
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Tex wrote:

Yes, but it still leaves one of the wires at 120V with respect to ground.
With a typical saw setup you could get a nasty shock if you turn off the machine with a single pole switch, then start working on the motor.
Of course, for safety I'd unplug the machine anyway before working on it, but still....
Chris
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Thanks for the help.
I took the switch apart and inside it says it is rated for 250v @ 20a. Then I checked both poles with an ohm meter and both open when the switch is off. So, it looks like the saw has a DPST 250v switch if I understand correctly. It would have been nice if they labeled the outside or manual, but it looks like I am good to go so I am happy.
-Steve
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I would want to test it with volt meter, though an ohm meter ought to be okay. You sound good to go.
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If you expected to seem credible, you just blew it. Toller normal.

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He blew credible in his first post, but then he always does in any thread about electricity.

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says...

Yes, that's why I don't like it. I guess at an a.c. compressor it's pretty isolated and not that much a danger. But, technically, "it sure ain't pretty" I realize it's cheap (in all respects to use of that term including, but not limited to, less expensive). So, to each his own - I'll buy something better.
Also, I wouldn't advocate switching ONLY one leg, particularly one where someone might, by whatever means, come into contact with a live 120 VAC leg on the downside of that switch. I admit I haven't checked the NEC to see where/when this is allowed/disallowed -- I just don't like it on esoteric/technical grounds.
On unplugging the machine -- I NEVER even change a blade without unplugging the connection. And, I have a 240 VAC magnetic switch between on/off.
For me, with power tools and firearms there just "ain't no way to be too safe"!
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Really? Let's review:

Huh? In this country (which country is that, by the way? Do you even know where I live?) I'm pretty sure I can switch 240V with a SPST switch (assuming it's rated for 240V). The test might be "does the motor work when I switch one leg of the two pole, single phase electrical service" which would absolutely not be true. Of course I could also be switching a 240V plate supply in a vacuum tube circuit, in which case a SPST switch is all I'd ever need.

Huh? Who said anything about circuit breakers? I certainly didn't.

In any circuit, if it is interrupted, it will no longer work. That's dirt simple, fundamental electronics. You seem unable to even grasp that.

Really? That's the first I've ever heard that. That will certainly save UL and a whole lot of other people a bunch of work testing switch dilectrics for voltage capacity.

Huh? So you're saying that when you want to change a dual voltage motor from 120V to 240V and the owner's manual says "make sure you have a 240v rated switch," your solution is to just fire it up and go. You don't feel any need to check to see if the switch is rated at 240V. Worse, you somehow feel the need to propagate that irresponsibility to innocent users who haven't as yet had a chance to witness your electrical incompetency over a period of time.

Huh? What does that have to do with the OP's question?

But not illegal. Intuitively (and solely from the safety standpoint), I would prefer to switch both legs, but I don't believe it's necessary (and it isn't necessary from an electrical standpoint).
So, in the final analysis, in regard to your statement:

I can only point out the obvious and say PKB.
Don't you get tired of embarrassing yourself? Stay out of electrical discussions and you will reduce your vulnerability 100 fold. You haven't a clue as to what your're talking about--just a few buzz words you throw together like monkeys at typewriters.
--
LRod

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It makes me nervous to read a manual that warns about the rating on the switch. Call Delta customer support and ask them. Sheesh, I hope this is not another way Delta is cutting costs.
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Call Delta with all model numbers in hand is the best advice . . . As to switches, somewhere they are marked, may be criptic, but marked. As to switch safety . . . AMP rating is what you are most concerned with . . . AMPS ! ! !
Steve

thing
The
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Steve DeMars wrote:

No, you need to take both into account.
If you take a 10V 100A switch and use it on a 10KV 1A line, you're going to have issues.
Chris
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Well I was trying to be practical . . . not what if . . ing last time I checked the average home did not have a 10KV line running to it . . . .

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Steve W wrote:

Electrical is more of my practical side:
The Switch (A regular switch that is) is ok if you flip it one way and the motor starts and if you flip it the other way the motor stops.
Here are some symptoms of a under rated switch: The switch gets hot to the touch Smoke coming out of the switch The motor stopped under load and won't start again.
If your switch has a UL or ULC rating, it will have it's ratings usually on the metal mounting plates. otherwise, I'd invest in another switch.
The RPM's of your motor are not relevant to the switch under normal conditions.
Hope I can help.
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False. The switch is ok if that occurs, *and* the switch is rated for both the voltage and the amperage that it's switching. Better still if the switch disconnects all of the hot conductors going to the motor.

If any of those things happen, wouldn't you say the switch was *not* "ok" ?
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Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

Must agree with the *and* part.

Yup, in this case *under rated* or *not* would in my understanding explain that the switch is bad or inadequate.

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Well, that's false also. A switch for a motor has to be rated for the hp of the motor. You can be okay on voltage and amperage and still fry the switch. It happened on my used table saw; the switch fused closed.
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