Wiring Diagram for Potter&Brumfield PM-17AY-120???

John,

Here's the data sheet on that relay:

and here's a clear picture: I would NOT wire the relay coil circuit from one hot leg to ground but to NEUTRAL. What do you have available in your shop with respect to 220vac power?

Contact me off the group if you like, I'll try to help you with some diagrams.

ARM

Sadly, I don't have a neutral, just two hots and a ground. But, the way I see it, maximum current through the coil is only 128ma, so that is the maximum running through the ground. Since the ground is a much better conductor than a person under even the worse scenerio, if you touched the ground wire (or the grounded body of the motor), you wouldn't get a measurable shock. And if the ground connection was bad, so that you would be the only conductor, the relay would open because the coil would lose power, so there would be no current at all. I just don't see any way this is dangerous. My kitchen oven has no neutral, the body is grounded, yet when the ground is carrying 7a (oddly, the bottom oven is designed to put only one leg of current though the broiling element when set to bake) I don't even get a voltage reading off it. It is the same situation isn't it? If it were hardwired it would be a code violation, but I just don't see how it could be dangerous.

If I am confused over this, please set me straight, because I don't need to save the $90 badly enough to risk an electrocution or fire!

Someone from the company that makes the ON/OFF switch on the saw was kind enough to talk me through it. The first row of 4 contacts is where the line connects. The second row of 4 is normally on, switched off when the coil is energized. The third row of 4 is normally off, switch on when the coil is energized. The fourth row of 2 is the coil. I connect the two hots to the first row, and the motor wires to the same contacts in the third row. They explained how to wire the ON/OFF switch, so I think I have that. I just can't figure out how it is now wired for 120v! It should be the same as the 240v, only with the neutral bypassing the relay completely, but they have wires all over the place. I am not changing anything until I figure that out.

If I have problems I will get in touch with you. Thank you, and please let me know if you find errors in my safety reasoning or my understanding of the relay!

I examined the existing installation more carefully, and the main thing is that they jumpered two parts of the relay. The relays says 1 hp max, 25a @ 277v max. I have a 2hp 16.6a motor. If my ampmeter is reading correctly, it drew 81a for a split second to start. (I wouldn't have thought you could force that much through 12 gauge) Presumably that is why they jumpered to two parts, to reduce the load on each.

Now, my current will automatically be cut in half when I go to 240v, so the load on the device won't be any greater; it just won't be much less.

What are the consequences of using a 2hp motor when it says 1hp max? I don't really care if the life is reduced, as 1) it has no other value to me, so I might as well replace it when it burns out as now, and 2) it has an expected life of 100,000 cycles, so 5% of normal life is still enough to last me a few years.

Are there more serious problems that could result from the overload besides shortened life? I really don't want to start a fire, though it is in a steel box.

I thought the price I paid for the saw was too low; but of course I can alway chuck the whole magnetic starter and put on simple double pole switch.

Don't wire it to ground. Only??? 128 mA?

128 mA will kill you! GFCI's protect against a ground fault of only 5 mA! DON'T WIRE IT TO GROUND!!!!!!!!!

That said, you have no problem. Just add a resistor in the coil circuit and you're good to go. At ~128 mA on a 120 volt circuit, the coil impedance is ~1000 ohms. If you put a 1000 ohm resistor in series with the relay coil, it should limit the current through the coil to ~120 mA. The resistor will get hot - it will dissipate about 15 watts of heat. To give yourself a bit of help in getting rid of the heat, I'd use

4 250 ohm 10 watt resistors in series. 1/4 of the heat will be dissipated in each resistor. I'd install them in a separate, ventilated enclosure with air space around each resistor, and install the enclosure under the bed of the saw after testing. To test, you would connect a voltmeter across the coil and look for about 120 volts when you turn the switch on. Precision is not important, but it is better to have the voltage across the coil lower than 120 versus higher. Adding more resistance in series reduces the voltage, adding resistance in parallel with one of the existing resistors increases the voltage. 10 watt cement power resistors sell for 55 cents apiece at Mouser.

Let us know how you make out. Here's a diagram:

hot-----Resistor---Coil----hot

There is a very confusing dialog happening in this thread. Anyway, I'm going to assume you are changing the saw from 240vac to 120vac. The load current of the 2hp motor wired for 120vac will be approx. twice that at 240vac. Paralleling the relay contacts will cause each contact of the pair to share that load. How the load current gets shared depends on the electrical resistance at the contact's connecting surfaces. The bottom line is that paralleling the contacts will probably work okay for your situation. You may have to replace the relay sooner than you think if it's the original one.

The next problem is the coil voltage. Again, I'm assuming the relay coil was originally operating on 240vac and you want it to work on 120vac. If you'll look at the datasheet for that relay (see the link that Alan gave -

) you'll notice that for the coil operating on 220vac it says - "Use a 110 volt relay with 2700 to 3300 ohm 5 watt wire wound resistor in series." So, to change it to 120vac (or

110vac) operation just find and remove those two 5 watt resistors that are in series with the coil. The coil itself (minus the resistors) is already wound for 120vac.

Perion.

I appreciate your concern, but I am unable to come up with a situation in which I could contact any current, let alone 128ma. If the ground is intact, I get no current because the ground is a much better conducter. If the ground is broken, I get no current because the relay opens. When could I get any current? Even if simultaneously the relay froze closed and the ground opened (both unlikely events), I still wouldn't get much current because I would be in series with the coil. What am I missing?

No, other way around; now set for 120v and I want to change it to 240v. They have the hot paralleled. I am intending on leaving it that way, and running the new hot through the remaining contact. (I can't parallel the second hot because I need a contact for the coil) So, will the unit be okay at 8a/240v with a 2hp motor, even though the specify 1hp max? I suppose it ought to be, since it worked at 16a/120v, and that was worse. But, I am mostly concerned about some failure more serious than simply wearing out.

I read that section about adding resistors as being for a DC coil. With an AC coil they want you to use their unit with a 240v coil. Presumably the difference in inpedence between a 120v coil/resistors and a 240v coil is sufficient to affect operations. Am I reading it wrong?!

Thanx

DO NOT use the ground wire under A NY circumstances A. It is a code violation B If the ground goes open then you will have 240 volts on the frame thru the relay coil and if the frame is at all insulated you will be dead Thats why it is a code Violation. Please do not tell me the GFCI will save you . It could fail too.

My real problem? I want to get a meaningful answer to my question.

1) Since only 120v is going through the coil, I can't possibly get 240v on the frame under any circumstances. 2) If the ground goes open, then the coil will lose power and the relay will open, so there won't be any voltage anywhere. I would have have the ground suddenly open (a most unlikely event) at the same time the relay got stuck closed (another most unlikely event). 3) Ignoring #2, I would be in series with the coil, so it would almost impossible to "be dead" even if I were standing in salt water when all this happened.

So I can't think of any situations under which it would be dangerous. Recognizing that I might have overlooked something, I am asking for advice. Just telling me it is dangerous without explaining how is not at all dangerous.

I suppose I could take the precaution of grounding the table saw frame independently to a water pipe, but I don't see the point of it.

I am sorry to say your real problem is trying to do something beyond your current training so the proper thing to do is get a licensed professional to do it for you. One relay and one change of voltage is really too fundamental to have elicited all the waffle that has gone on here. Get a 240 volt relay and someone who understands electricity and is licensed and all will be well. I am sorry if I am too direct but it is

Can't say if you are direct or not, because you haven't said anything intelligible. If you either don't understand the question, or don't know the answer, then just don't answer it. To babble something extraneous and then insult me is pointless.

You want to connect your 120 volt machine to 240 volts. Right? You do not know how to connect the existing 120 volt relay. Right? Then-------- Get a 240 volt relay and someone who understands electricity and is licensed to do the work and all will be well.

What did I get wrong or what can you not understand????

You got it wrong when you told me:

1) I will have 240v on the frame, which I will not because there is only 120v going through the coil. In fact, it would be impossible to have 240v on the frame, no matter how I wired it! 2) That I should not rely on a gfci for protection because it could fail. Uh, if I am deliberately leaking 128ma to ground, how is a GFCI going to work? It couldn't, or don't you even know how a GFCI works? 3) You say that I would die if the ground opened. That means you don't know how a magnetic starter works, because the power would be cut off as soon as the ground opened. (The OFF switch works by cutting power to the coil, which also happens when the ground opens. Duh) It also means you don't understand anything about electrical safety, because there is virtually no chance of death from touching a 120v line after it has passed through a coil that only draws 128ma; especially when the machine frame provides a better alternate ground than a person.

Are you aware that most electric dryers and ovens use a common ground/neutral? I didn't think so. How many die annually from being electrocuted from open grounds? Geez, and they don't even have relays that would cut the power if the ground opened.

So, what did you get wrong? Everything.

Yes I said 240 when it should have been 120 but remember the civilised world uses 3 phase 415/240 volts. Sorry for my typo.

I will just be brutal.

IF you are such a KNOW ALL how come you did not know how do do this and break some safety rules without asking us??

So; you concede you don't know your ass from a hole in the ground, but think you have a right to be brutal? Think again.

I thought we beat the shit out of this subject a week or so ago and came up with putting a 3k resistor in series with the coil.

I made an assumption or typo that had no real effect on the outcome so why be abusive??

As soon as the argument exceeds your intellect you descend to abuse. Too bad So Sad.

Someone suggested putting a 3k resistor in series with the coil. I looked at the spec sheet, and it looked to me that it was for a DC coil only. I posted that as a reply. No one has commented otherwise.

Have you read the sheet and thought it was for A/C coil also? Please let me know.

Resistors work the same in AC or DC. If the apparent ohms (volts/amps) of your coil is 3k or so a 3k series resistor will split the voltage 50/50. There are more technical was to describe this but this is basically the way it works. If you have a meter you can verify you picked the right resistor be measuring the voltage across the resistor when it is on. Get something around

10 watts. It works out to less than 5 watts but for the few extra pennies it is better to have one that has some extra heat handling capability. I imagine you can get a 3k 10 watt resistor at radio shack.