Creative version of a 3 phase switch?

[BadDog]

I recently completed a somewhat involved repair of a Powermatic 20" drill press project I purchased some time back. I had it up and running shortly after acquisition when I determined the repair was more involved than I had time for, so it got put on hold. In the process of finally finishing the repair, I had to remove the motor. Now I'm no longer a machine shop newbie, and I've become pretty comfortable with 3ph motors and controls in my shop, including designing and building my own multi-stage RPC along with a number of rewires and repairs.

So when it came time to remove the motor to complete the repair, I didn't really pay much attention to the connections in the box during disassembly. Then I went to wire it all back up and realized the 2 3-wire cords leading to the switch had only 2 conductors stripped. So I checked it to the switch, which turned out to be a standard 2 pole Leviton "professional" switch from a big box store, no contactor nothing but the switch. The only thing that made sense is that the remaining wire was tied straight to one of the phases direct into the motor. Hmm, maybe I should have paid more attention when removing...

So looking at it I thought, "That can't be right". But nothing else made any sense, and I know it ran without any drama in the past. So I decided to throw the dice and see if it would run like that. It surprised me quite a bit by not particularly caring that one lead was hot all the time. The motor didn't hum, didn't appear to be getting over heated, no drama at all that I could tell, started and stopped just as it seemed it should. At least I got to test out the repair a little bit to confirm at least initial success.

So is this acceptable and it's just one more thing I never knew? Or is it as it seems it must be, and not a good idea at all to keep one of the coils energized all the time when the 3ph circuit is hot?

For grins, I decided to check my other big drill press since it employs an almost identical design. It's a big US made Wilton 20" VSG. Pretty much identical press, but a bit heavier built, and much lower over all speed range. Sure enough, it had all 3 hot lines routed to a 3 pole switch, just as I had expected. What I did NOT expect was the insulator on the red wire for the entire machine (all the way from the wall) had gotten hard and brittle, crumbling off leaving bare conductor. WOW! The wire appears to be good wire, possibly OEM, and everything remaining nice and flexible/pliable except the red insulation that is disintegrating. Now I'll have to rewire that too before I electrocute myself or burn down my shop, but at least it has a proper 3ph switch...

[spro]

I agree it isn't right but has been done. All kinds of things were done when machinists weren't necessarily electricians. I don't like a live field sitting there either. A cheap disconnect box with spade fuses may be the way to go.
Btw great work on that motor shaft and the tip about the relief channel is priceless.

[dly31]

A two pole switch on a three phase motor is unsafe and not permitted by any codes I know of but it works perfectly well.

[hammermill]

if memory serves me right the switch is a common 4 way switch used in multilocation lighting circiuts. but it would only swap the 2 wires not provide a on/off

seen it done but not safe in most instalations.

[spro]

That's what I meant too. It can work when there and then cut off the live leg/s when not. Something good came of the investigation of the other large drill press. We don't know how this works but finding that problem, means a lot.

[BadDog]

I agree. The Wilton VSG is in top shape and I would never have had any reason to look inside if not for this coming up. First thing I would have known anything was going on would likely have been when something went "pffFFUT!" with a bright flash of light, or a tingling in the finger tips (if I was lucky, a rare thing indeed).

And it is a true 2 pole switch. Both open, or closed at the same time. But I have a number of smaller contactors (5HP or so) I stripped from commercial HVAC controls. I expect I'll rewire it with a single pole switch and contactor. My biggest problem is most of those contactors are 24V coils, so I'll need to either shoe horn in a transformer or find a 110V coil.

At the moment I still feeling more than a bit nervous with that existing 2 pole switch, though not as much as I was. But it's not like I'm short of projects, and my other big drill is down for now which puts the newly functional Powermatic front and center, so I guess we'll see what I've got done when the next large drill hole needs drilling.

[spro]

I mentioned a cut off box with spade fuses or cartridge fuses because the cut off switch box usually had fuses. It is only cut off. Your other stuff with contactors would be fine when it is on. These are pretty all right, spring loaded knife switches and sound like a 22 when tripped by handle.

[hammermill]

my mind went the wrong way thinking of motor reversing. indeed a 2 pole switch would have turned things on/off

if you are saivaging hvac coils, net time grap a transformer too as you well know 24v is most common

[BadDog]

spro:
Absolutely, it would certainly provide for eliminating the concern with the live coil when the machine is not in use. I've even got one of those boxes along with some other cabinets from large to small on the shelves. It would certainly be easy and pretty bullet proof, but I'm leaning toward a more integrated single-point control solution.

Hammermill:
No worries. But sadly, that's a thing of the past. I used to have access to those salvage those things, got a bunch of nice AB switches and lights, Furnace (etc) contactors, nearly virgin (other than a few button holes and such) NEMA cases, etc. But I only grabbed a few 110/24V transformers. And at this point, would have to dismantle something to liberate a 24V transformer for re-use. The only thing that would be a likely donor is the 3-stage RPC that uses a complete 24V control circuit. But that thing is one of the cooler things I've built, and even though I don't need it any more, I really don't want to dismantle it. They also tended to be rather larger physically than this circuit would tolerate without adding another box, which I would rather not have to do. Fortunately, the 110V coils aren't usually that hard to come by, and make the whole thing more compact.

[tornitore45]

A two pole switch on a three phase motor is unsafe and not permitted by any codes I know of but it works perfectly well.

Don got the essence of this problem right.

Is equivalent to to place the switch on the withe wire on a bulb. The bulb is not energized but the lamp and the socket are hot at 120V. No current the lamp is cold but plenty of voltage to be unsafe poking around or in case of insulation breakdown.

[hammermill]

you dont see many anymore but consider its operation in a building with a corner grounded delta that third leg would be grounded.???

[BadDog]

Sorry, I'm afraid I don't follow. I'm familiar at a functional level with typical 3ph, but I don't have any real background.