Electricals: what kind of switch do I need for this?

[Cursitor Doom]

Hi, leccies,

I've got this single to three phase converter running a lathe motor;

230v in, 230v out. I'd like the ability to swap phases over so I can reverse the motor to run the lathe in the opposite direction should the situation call for it. The motor's max current draw is just under 30A. What's the technical name for the kind of switchbox which could be wired up in series with the converter's output to swap a couple of phases over? Or better yet, a link to a suitable product on the web?

cheers, cd.

[harryagain]

Google:- "three phase motor reversing switch."

[Cursitor Doom]

Thanks. I was just hoping there might be something off-the-shelf I could get from my local electricians' supply company. Would a more conventional switch not work??

>

[Nightjar]

I would be surprised if they couldn't supply one, either off the shelf or next day.

You need a three-pole 2-way centre off switch, with two of the poles' outputs cross-wired.

Colin Bignell

[John Rumm]

Any Double pole Double throw switch can be wired to do that...

feed L1 and L2 into one side, connect the other side to L2 and L1 (i.e. reversed) and connect the common to the load.

[Andrew Gabriel]

Or even an intermediate light switch (not at 30A though).

[meow2222]

2 pole 2 way, aka DPDT, or a crossover switch would also do it

NT

[Tim Lamb]

Umm.. might be nice to have *centre off* at least or some link to break the converter output where the lathe is running at speed.

My ancient Boxford had a simple rotary switch before I converted it to single phase. I sometimes wondered about the likelihood of unthreading the chuck:-)

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[Nightjar]

Possibly not, if you are using a DPDT switch only as a reverser as 'off' would still leave one phase connected. IMO the right way to do it is a three pole two way centre off switch.

IME, something that is not that easy to do even hitting the chuck key with a large hammer.

Colin Bignell

[Cursitor Doom]

Got a camlock system on mine so it's not a problem. :-> Cheers for the advice, gentlemen. Nice to know I'm not going to end up installing something that would be dangerous or in violation of the Regs.

[John Rumm]

It kind of goes without saying, that flipping the switch with it running would not be a "good thing" (tm)

Perhaps a better solution would be to use a DPDT contactor to do the actual switching, and wire that such that its locked out when the lathe is running.

Lots of lathes seem to use quite aggressive breaking on the chuck these days - so its probably not that easy to do by accident.

[meow2222]

Indeed. The motor would survive it though. To discourage it you could always size the fuse to pop if someone does that.

A 3 position switch isnt going to solve deliberate abuse. If you only switch 2 wires you should definitely not use a 3 position switch, it may result in a burnt out motor.

NT

[Nightjar]

That is starting to get more complex (and probably more expensive) than simply using a three-phase reversing switch.

IME often quite difficult to do on purpose.

Colin Bignell

[Cursitor Doom]

Yes, and a pity on one seems to make such a beast. You'd have thought it a common enough requirement, wouldn't you? I mean, a switch which just swaps two wires over, but apparantly they don't exist! That's what the two biggest electrical factors where I live have just told me, anyway. I've never seen service counter staff look so completely baffled. :-(

[Nightjar]

You probably need a machine tool or control gear supplier, although you can always assemble your own:

Colin Bignell

[Dave Plowman (News)]

We had a lathe at school - many years ago - that had a rotary switch to reverse it. Three position - centre off. It was such a chunky device likely no contactors involved. But H&S would have a fit today.

I'd say you'd have more chance looking for something like that at a machine tool place - rather than a general electrical wholesaler.

RS components do a number of rotary switches designed for the job. One such is the 20 amp 350-5615 which is about 15 quid bare - but you'll need a handle and enclosure.

[Nightjar]

On 29/04/2014 16:31, Dave Plowman (News) wrote: ...

The Dewhurst drum switch? The only thing between you and 415v being a bent piece metal held on with a single screw and two metal lugs. The cover is back to front on the top image here:

Colin Bignell

[Cursitor Doom]

Yeah, but times move on. Remember the early electric kettles with the two bare terminals at the back? The thing was in those days, electrics were so dangerous that you didn't misuse them - or you died. It sharpens the mind wonderfully, don't you think? That's the problem with all this health n safety these days; it's making people very careless.

Anyway, panic over. I have discovered that buried within the menu system of the phase converter that drives this motor is an option to reverse the drive. I thought there HAD to be one in there somewhere, given the astonishing number of other less vital options the damn thing boasts. Other models have the switch prominently on the front panel, but not this one for some strange reason. :-/

[tony sayer]

In article , Cursitor Doom scribeth thus

A mains/generator changeover switch would be the thing for this, it's a double pole changeover switch with Break before Make being the important part!...

You surely don't expect the man behind the counter in an electrical wholesalers to know that much about actual circuitry do you;?..