I have 2 machine tools both 3 phase. I have a phase converter. I have been in the past, just pulling the 3 wires from the motor off of the converter, and plugging in the motor wires from the other machine. Its a bigger pain that it sounds. I am looking for some kind of swith to just switch between the two without having to pull wires. ANybody know what I should be looking for? Thanks for the help. if trying to email me direct, email snipped-for-privacy@savant-us.com Thanks
Ask your electrical supply store for a "manual double throw three phase transfer switch" with sufficient ampacity for the heavier of the two loads. Wire it in where you can easily reach it to throw the handle.
Lots of companies make them.
If cost is a factor and you've got a well stocked electrical junk pile, but no transfer switches in it...... You could use a couple of three phase disconnect switches (fused or unfused) and rig some kind of a mechanical interlock between them so that they won't both be "on" at the same time. It shouldn't take much more than appropriate mounting locations and some sort of center pivoted lever to accomplish that. (No warranty from me on an electrical or insurance inspector "buying" it though. )
Do you mean a static phase converter, a rotary phase converter or a VFD?
If you don't have a VFD and your machines have their own power switches, you can keep both machines hooked up to the converter, you don't need a switch. If you have a VFD its best to use a switch.
That's what I do with my 3 phase machines that do not have VFDs. As long as the wiring is adequate, in most case there's no problem starting another machine when another is already running, with either a static or rotary converter. In other words, I don't understand why the OP feels it's necessary to have only one machine connected at a time.
I do have a pair of 30A motor starting switches wired as Jeff describes above to select either the rotary or static converter. One switch is mounted upside down and a bar between the handles prevents both from being on at the same time.
Hey, thanks Ned! I thought I was going to get all sorts of jazz from folks for that "interlock" suggestion.
My first thought was to recommend your "upside down" (and I presume offset by one width.) trick, but I wasn't sure how much an upside down disconnect switch would agitate an inspector.
That reminds of what some critic called Laurel and Hardy...."Two minds without a single thought.."
Not sure I follow EXACTLY what you mean, but what I have done is gang-mount three sockets for clothes dryers (6 bucks Canadian each) side by side on the wall, all inter-connected as three phase ( instead of two hots and a neutral). The 220 circuit breaker feeds two of these legs. Then for my purposes, I've scrounged up five used plugs from old clothes dryers (new = 15 bucks each.......at garage sale, a buck or two). I've hooked each individual motor's leads for the machines to the individual dryer plugs, including the rotary phase convertor. For two of them, the cord set itself is long enough, and for the other three I just joined the motor cab-tire to the cord set with wire-nuts and taped them all up. Bit lumpy, but not bad if you're neat. So I just plug in as required. Very simple, and I can have just 220 single phase for a welder or whatever, by not wiring the neutral on the plug.
Sorry if I've mis-understood, and this isn't what you meant.
Take care.
Brian Laws>I have 2 machine tools both 3 phase. I have a phase converter. I have
Inspector? You need a code before you can have an inspector. This is a town with no shortage of multi-million dollar waterfront homes with no building code or electrical code. The State of Maine does require towns to have a plumbing code and shoreland zoning, but that's about it.
Here's a photo of the switches...
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If anyone wants to do something like this I have quite a few of those switches, 3 pole 30A @ 600VAC, 7.5/15/20 HP @
240/480/600 VAC 3 phase.
Speak for yourself, I thought it was pretty clever .
My commercially made MTS transfer panel works that way. It is impossible to have our generator connected to the panel and still be connected to the service. It's a slick way, and perfectly acceptable by code. They use a Square D panel and add the interlock. Real slick system.
I'd be surprised if there isn't a short delay in the transfer from generator to utility, and not just an inter-lock. Except on very expensive systems that do phase monitoring. In fact, even from utility to generator during routine test. Actually, part of this is occurs naturally as the switch gear is "centre-off" and not centre-shorted. Common "timing" on emergency power is 13 seconds from loss of utility, and at least two cycles for strictly resisitive loads, but we required a 15 second advance warning of transfer to shut-down to keep from damaging our MG sets.
They are pretty much gone now-a-days in favour of Robonic transfer switches, but there were lots of fair size systems that had emergency (called "auxiliary" today) systems where individual circuits were hand-switched with three-pole-double-throw disconnect, where Up was ON, Centred was OFF, and Down was ON. I've seen them from as small as
60 Amp up to 500 Amp. Mind you, I would not be too hasty to have to throw the 500 myself!! With this system, the "load" is connected to the "centre" or moving poles, and the "up" was normal or utility, and "down" was the auxiliary. I even recall quite an elaborate system of chains and pulleys, connected to various of these disconnects, to "force" the operator to "do" the switching in a required sequence.
I probably should have been a little more specific when I talked about my panel. We have just a small (5 Kw) single phase generator that we can use in an emergency, enough to power our boiler and a few other things. I've wired enough things through the panel that I can, by selective switching, run our well, heat, alarm system, freezer, refrigerator, and water heater, just not all at the same time. While we've not been through it yet, I've been told that power is known to be off for a few days in our area when we have severs freezing rain storms. So far we've dodged that bullet, including last January when Portland got slammed. It started out freezing here, but about an hour later it changed. We were high enough that the inversion held the cold air at a lower level. Very lucky, at least that time.
The panel of which I spoke is a real simple device, must be switched manually, and I even have to plug in the generator, although it would be left plugged in and in position if desired. It has a couple breakers mounted back to back with a slide that doesn't permit both the generator and the line to be connected to the structure at the same time. That way it can't back feed into the entire grid system.
By the way, you're making me drool with the idea of having a large one that switches as you describe, especially if it was 3 phase. I came very close to buying a 15 Kw 3 phase generator while I was still in Utah. There are times when I wish I had. It was a surplus military unit with sound proofing enclosure, diesel powered. Appeared to be in excellent condition.
Does that switch transfer BOTH the hot and neutral wires? If not, there are circumstances where you COULD send power back into the grid.
Any method you use to connect a generator MUST transfer all wires except the ground off the grid. You might work something up with switches intended for 3-phase that would allow a proper transfer.
Here is something I wrote in rec.boats in Sept 99:
[I asserted that it was possible to feed power back into the grid if only the hot lead was transferred. Another reader said the breaker would trip first.]
Here is a google-groups url that will take you to the original post; you can get to the whole 47 message thread from there:
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you have trouble cutting and pasting that long line try searching google groups using advanced search for: all these words: hot neutral generator author: peter meek
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