16 CW power switch question

I need to get a new switch for my lathe and I'm a little confused about what I need. I found what looks like a possible replacement (unfortunately, I don't have the original switch) here: SQUARE D Control Station, Push Button, 2NO/3NC - G3281004 at Zoro

I'm confused about it being a "Momentary/Momentary/Momentary" type switch, does that mean I have to hold the button down to keep the spindle running when the clutch is released? Should I be looking for a Continuous/Continuous/Continuous switch?

Also, the link above is rated at 5A @ 600v, will that be compatible?

Thanks in advance...Craig

This unit controls the main contactor (a reversing magnetic starter - in a big box on back of head stock on my CW) and momentary means you push the desired button and lift your finger

That operator station (switchbox) is just a signaling device. The reversing starter John mentions is doing the heavy duty current switching to start and stop and reverse the motor.

Abbreviated 3phase motor theory says "reverse any 2 of 3 lines to reverse rotation". Typically a reversing motor starter has two identical contactors wired A-B-C and A-C-B (or the like, just switch any two wires). A very serious problem can arise if both of the contacts happened to close at once, in my example B and C are dead-shorted to each other. This is very bad not good and will cause big inrush current up to the current limiting capacity of something else upstream.

So, to protect against this each contactor in the set also actuates a normally closed contact (then going open circuit) that is just a signaling contact for the control voltage. That NC contact is wired in series with the opposite coil, essentially one relay blocks the other one, you can call it "inhibit" or whatever comes to mind.

There is also the basic "seal" circuit, where another normally open (NO) contact holds its own coil steady after the initial impulse from the FWD signal. The perpetual state is broken by normally closed STOP pushbutton being depressed.

Clear as mud? I probably jumped pretty far ahead, even though I was trying to simplify some concepts. Somewhere I have a couple of diagrams to help illustrate. They are a little crude and hand-drawn, but just a brainstorm on how to illustrate captured from a few years ago. Hopefully this was helpful.

This is the basic "seal" circuit...


More about the rest of the circuit...MS = Motor Starter, OL = overload as in a thermal overload.

John and Matt,

Thanks for the help! Yeah, that description is a little over my head Matt but I think I have a general idea. If I understand correctly, I need to match the 2NO/3NC of the above control box to a suitable reversing magnetic switch right? Or do all reversing magnetic switches work the same way, you just have to wire it correctly like your diagram above?

There is a loose wire that looks like it went to a switch at one time. I'm going to have to get behind the lathe and see where it goes to see if a reversing magnetic switch is already present. If there isn't one, it sounds like I would need to get the control box above and then also get the reversing magnetic switch right?

I pride myself on trying to figure things out but man, this lathe is kicking my butt at the moment, LOL.

Thanks guys for taking time out of your day helping me to understand all this .

In the reversing magnetic motor starters which I have, there is a mechanical interlock present which physically prevents both FWD and REV from being selected.

The auxiliary contacts are in addition to the mechanical interlock.

The older (pre-NEMA ?) reversing magnetic motor starters have two overloads ... one in the A phase and one in the C phase ... the B phase has no overload.

Also, it is A and C which are reversed ... B is not reversed.

peterh5322 said:

The older (pre-NEMA ?) reversing magnetic motor starters have two overloads ... one in the A phase and one in the C phase ... the B phase has no overload.

Also, it is A and C which are reversed ... B is not reversed.

Click to expand...

Peter,
In this situation where would the generated leg of RPC be? The B / center contact with no overload or does it even matter?
Thank you
Rob

You can't miss the one (reversing starter in its enclosure) on my CW - it is about 8 wide, 6 deep and 20" tall

The pair of contactors is "stacked" rather than side by side

kumaichi said:

John and Matt,

Thanks for the help! Yeah, that description is a little over my head Matt but I think I have a general idea. If I understand correctly, I need to match the 2NO/3NC of the above control box to a suitable reversing magnetic switch right? Or do all reversing magnetic switches work the same way, you just have to wire it correctly like your diagram above?

There is a loose wire that looks like it went to a switch at one time. I'm going to have to get behind the lathe and see where it goes to see if a reversing magnetic switch is already present. If there isn't one, it sounds like I would need to get the control box above and then also get the reversing magnetic switch right?

I pride myself on trying to figure things out but man, this lathe is kicking my butt at the moment, LOL.

Thanks guys for taking time out of your day helping me to understand all this .

Click to expand...

johnoder said:

You can't miss the one (reversing starter in its enclosure) on my CW - it is about 8 wide, 6 deep and 20" tall

The pair of contactors is "stacked" rather than side by side

Click to expand...

The black box at the top with L1, L2 and L3, is that wire going to the switch or is that power coming in? I'll try and get some pictures tonight of what is hanging off the back of my machine, I'm hoping it looks like yours.

"In this situation where would the generated leg of RPC be? The B / center contact with no overload or does it even matter?"

I would place the generated phase in B.

A and C would be real phases, not generated ones, and those are the ones which have the lowest source impedance, hence pose the greatest threat to the machine in an overload situation.

B is kind of a catch-all.

In the old (and now deprecated) grounded delta, the grounded phase was assigned to B.

This connection allowed use of a common 120/240 single-phase panelboard (load center) to control three-phase systems. There was the gounded B phase neutral bar and an additional neutral bar for the protective ground ... the first for circuit currents, the second for fault currents. In these cases, these were not neutral bars at all, as there were no true neutrals.

Probably only of historical interest these days, but in a prior lifetime, as an EE at this nation's largest municipal utility, we had a number of 240 grounded B and even 480 grounded B installations.

It is certainly not the best practice, from a safety standpoint, but it is the lowest cost option for three-phase premises distribution.

kumaichi said:

The black box at the top with L1, L2 and L3, is that wire going to the switch or is that power coming in? I'll try and get some pictures tonight of what is hanging off the back of my machine, I'm hoping it looks like yours.

Click to expand...

"Black box" is just the arc shield, easily removable and the main three legs of incoming three phase are connected there. (the big black SO cord there in the photo was for initial testing)

A suggestion will be to DIVORCE your thoughts from main power when thinking of the "switch" (push button station), because it only has to do with the COIL CIRCUITS. I.E., in the simplest terms, pushing the start button merely turns on an electro magnet - which works the contactor in the big box - with an authoritative CLACK!.

As far as RPC operation, I'd make sure that the "real" phases from the house panel powered the control transformer. Otherwise you are bound to get chattering relays and other weird behavior as the generated leg sags under the starting load, and thus the control voltage sags, coils lose magnetism, etc. Done that already once and it was all fixed by rearranging as above.

IF the two magnetic motor starters are stacked on top of one another, it becomes quite difficult to implement the expected and required FWD/REV mechanical interlock, but it is not impossible.

I have a number of reversing magnetic motor starters where the mechanical interlock is provided by a simple wig-wag arm.

In such a case, the extra contacts are not required.

The 10EE's FWD and REV contactors are implemented in this way.

Here's what I'm looking at, I apologize for the bad lighting, it's hard to get to the back of the lathe .

That is indeed a standard interlocking (FWD/REV) magnetic motor starter.

Since it is Allen-Bradley, perhaps you could download the catalog section or sheet which applies to that specific model.

Basically, what manufacturers do is place two identical magnetic starters on a sub-panel and then semi-permanently wire A to A, B to B and C to C on the line side, and A to C, B to B and C to A on the load side, and, finally, install a rocker which allows either solenoid to pull-in, but only one of these at the same time.

Sometimes the inter-terminal wiring is just stranded wire, sometimes it is bus bar. Depends upon the manufacturer and the model.

Do note the coil voltage. If not line voltage, a small control transformer (about 50 V-A) may be required.

I received my control station today and I'm perplexed. I have three wires coming out of the machine that at one time went to a switch. I opened the control station and there are 10 terminals (see image below). My assumption is that some of the terminals need to be "jumped" in order to work for my situation. Is this a correct assumption? I can see from the sticker inside the housing that terminals (1,2), (5,6) and (9,10) close the circuit. Is that right?

Also, the buttons don't stay depressed so I guess they work by sending a signal to the solenoid that maintains its "contact" keeping the direction "locked in" until either the other direction button is pressed or the stop button is press releasing the solenoid. Is that a working description of how the control station works?

On your switch terminals (1,2), (5,6) and (9,10) are NC (normally closed) contacts and (3,4) , (7,8) are NO (normally open) contacts. The NC contacts will stay closed (complete a circuit) until their prospective button is pushed at which point they will open and no longer complete a circuit. The NO contacts will stay open until their button is pushed at which point their contacts will close and complete a circuit.

The magnetic F/R starter switches have an auxiliary set of contacts on them that close when the Mag switch closes. Power is routed through these contacts to the magnetic coils allowing them to stay energized after the Forward or Reverse buttons have been released.

Thanks BuckyM1A, as per your suggestion, I have the jumpers installed (see picture below). I think I know which one is power but wanted to double check. The Red and Turquoise wires look like they activate the solenoids, I don't know which one is FWD or REV but once I get it hooked up I can always switch them if they are reversed. The black wire looks like it's connected directly to the transformer which should be my hot wire, right?

To finish my switch, would this be correct:

Black wire goes to terminal 10
Red wire goes to terminal 3 OR 7
Turquoise wire goes to terminal 7 OR 3

Please see the pictures below.

Thanks again for the help,

Craig

Its just me, I know a lot of old machines were built like that but I'm not keen on full line voltage running thru an operator station. I haven't been totally beaten down to 24vdc but a 50VA control transformer running a 110vac control voltage would make me sleep better at night. That said, for this situation it would add complexity with ice cube relays or else a newer NEMA1 starter assembly being purchased and used.

The way the relay/contactor/starter/magnetic jobbie works when you release the pushbutton is the "seal" circuit in red. Simplest way I can think to describe that. Understand, inherently, how that simple circuit works and you can wire motors, you can write, edit and modify PLC logic. IMO a pretty powerful concept invented by those extremely smart people who came before us.

Free advice, make sure the metal operator box has its own separate copper ground wire that's confirmed attached to the machine's incoming ground wire, (eventually) going back to the ground in your circuit panel, all the way in copper or connections to copper. In other words, thru the machine chassis as a conductor or thru the machine base thru a conduit locknut to the sheetmetal of a contactor panel would not pass my proposed criteria.

Ok, after getting some sleep (giving electrical advice when tired is just a bad idea ). There are basically two ways to set up the wiring. One will require you to push Stop between directional changes, the other will let you go directly from forward to reverse (plug reverse). Its a little more work but personally I would go for option two, Just my personal preference. However, either way, you seam to be missing some wires.

Option one:

Requires four wires: Power in, Power out to hold, power out to Fwd, power out to Rev

Assuming that power for the mag coils is being supplied from a transformer, basic wiring will be something like this: One wire from the xformer will go directly to one terminal of each of the mag coils. The other wire from the xformer will be Power in, and will go to terminal (10). A Jumper will go from terminal (9) to (8) and (4). Power out to Fwd will connect to terminal (3) and power out to Rev will be connected to terminal (7). Finally power out to hold will also be connected to terminal (9).

Back to the mag switches. The power out to hold wire will be connected to one terminal of both of the hold (auxiliary) switches. The other terminal of each of the hold switches will be connected to the second terminal of their prospective mag coils. Finally the power out to Fwd and Rev wires will also be connected to the second terminal of their prospective mag coils.

If the hold switches have both NC and NO contacts you will want the NO contacts.


Option two:

Requires five wires: Power in, Power out to Fwd, Power out to Fwd Hold, Power out to Rev, Power out to Rev Hold.


Assuming that power for the mag coils is being supplied from a transformer, basic wiring will be something like this: One wire from the xformer will go directly to one terminal of each of the mag coils. The other wire from the xformer will be Power in, and will go to terminal (10). A Jumper will go from terminal (9) to (6) and (2), another jumper will go from (5) to (4), and another jumper will go from (8) to (1). Power to forward will be connected to terminal (3), and power to Reverse will be connected to terminal (7). Finally, Power out to Fwd Hold will be connected to terminal (1), and Power out to Rev Hold will be connected to terminal (5).

Back to the mag switches. The power to Fwd hold wire will be connected to one side of the hold (auxiliary) switch on the forward mag switch, and the Rev hold wire will be connected to one side of the hold switch on the reverse mag switch. The other terminal of each of the hold switches will be connected to the second terminal of their prospective mag coils. Finally the power out to Fwd and Rev wires will be connected to the second terminal of their prospective mag coils.


Again if the hold switches have both NC and NO contacts you will want the NO contacts.

This really is easier to see than to explain. There is a decent schematic here ->
http://literature.rockwellautomation.com/idc/groups/literature/documents/wd/gi-wd005_-en-p.pdf
Pages 27 and 28 of the pdf.

Here is a quick drawing I did for option two:


Hope this was more helpful than confusing,
Jim