EDIT.....

i think the ON (?) switch sends power to the bottom ( black wires) to energize the coil  ( single phase, or 1 of the 3 phases) to pull the contactor UP or DOWN...  there is probably 3 sets of contactors at the top that connect the wires on the LEFT to the wires on the RIGHT... So it looks like an ON- OFF, 3 phase power to the motor switch.

Since there are TWO BOXES, it could be to run a motor forward or backward.. reverse direction ?

As Steve says, they're contactors.  The contacts are at top, and the coil is at the bottom (black wires).  Energize the black wires, and the electromagnet coil on bottom will pull the contacts together.

MOST LIKELY, the two contactors are wired up so that one of them will run motor forward, the other will run it in reverse.  There's 3 leads going to a 3-phase motor.  Call them A, B, and C.  The motor has three leads... call them X, Y, and Z. 

Hook up

A to X,

B to Y,

C to Z, and the motor turns in one direction.

Switch ANY TWO wires, and it will run opposite direction... so

A to X, B to Z, C to Y... and so on.

IF There's only two contact sets on the contactors, and it's three phase, there's three leads.  The way it works is simple... ONE of the incoming power leads is always connected... let's say A to X.

To make it run one way, B-Y and C-Z

To make it reverse, B-Z and C-Y.

In this example, it only takes two contactors, each having two sets of contacts.  When ONE contactor pulls in, it makes the B-Y and C-Z connection.  When the other pulls in, it makes the B-Z and C-Y connection.

Your switch, therefore, needs to just connect control power to one contactor, or the other, to get a 'run forward' or 'run reverse' command.

Just gotta make certain that ther's NO WAY that you could ever have BOTH pull in at the SAME TIME... they have to be mutually exclusive, lest you have B shorted to C.

BTW... a contactor is oftentimes referred to by some as a 'relay'... and while they do the same thing, a contactor is different for one very basic reason:

When you energize the coil of a relay, the contacts it controls close... and as long the coil of the relay has power, it will continue to hold them closed.

And the relay coil will continue to draw the same amount of power.  Let's say the coil of the relay requires 2 amperes to pull in, and once it's in, it continues to require 2 amperes to hold those contacts.

A CONTACTOR, however, is an AC device that, when it 'pulls in', the AC coil's polepiece is 'contacted' by the armature pulling in the contacts.  When the armature lands AGAINST the coil's polepiece, two things happen- first is that the armature becomes part of the polepiece's magnetic 'world', and it holds extremely tight, and second, the 'magnetic world' of that armature and coil now 'restrict' the amount of AC current that can flow through the coil... the property is called 'inductive reactance'...

so the end result, is that an AC contactor might require the same 2A to pull in, but once in, the coil naturally LIMITS the amount of current flow through the coil... say... to 1/4A... and as a result, it not only reduces waste energy significantly, it substantially increases the coil's operating life...

IF you come across a contactor that's buzzing when it's pulled in, shut the machine down, carefully disassemble the contactor's mechanism, clean it all up good, especially the pivots and the armature/polepiece faces, and put it back together... it'll pull in solid, get a whole lot quieter, and run cooler.

Okay, so there's 2 speed motors, and there's backgear gearboxes.  I wouldn't be surprised if yours has BOTH a 2 speed motor, and a backgear box, but it wouldn't surprise me if it just had one or the other.

A 2 speed motor (aka, a "Dahlander" motor, named for the Swede that invented it) is a 'consequent-pole' motor... it has two sets of windings... basically, it will run in a 2-pole (1 rotation per AC cycle) or 4-pole (1 rotation every two cycles) mode, for (in USA 60hz world) either 3600 or 1800rpm.  If it was a really BIG motor, it might run in 4 pole/8pole mode.  (I'm not certain wether one could Dahlinder a 4 pole/6pole without using a really huge switch, on account of the crazy contact wiring).

Anyway, the high-low speed setup on a consequent pole requires more than just two contacts to make the motor run, so if you see a contactor or switch with LOTS of contacts right before the motor (and there's lots of wires coming out of the motor) then you have a consequent-wound dual-speed motor.  Don't disconnect any of those, it'd be a real challenge to sort them all out in the future (without a diagram, and missing a few wire labels... it'd be a nightmare)...

One thing that may confuse you... on the reversing switch, you MIGHT find that there's another mechanism and switch that reverses the reversing switch... and if so, that mechanism is probably tied into the backgear shift mechanism.  Why?  Because many backgear mechanisms, in doing what they do, inevitably wind up reversing the spindle direction... so when you throw it into backgear, reverse becomes forward, and forward becomes reverse (Johnny Depp... Captain Jack Sparrow... Down becomes up, and up becomes down, right?)  So they put a reverser-reverser in there, so forward is always forward, even when it's reverse.

Are you confused yet?

Here's a connection schematic that was in a post on PracticalMachinist:

http://www.practicalmachinist.com/vb/attachments/f11/27411d1287940424-220-440v-nameplate-2-speed-motor-changing-voltage-wiring-s-s-contactor-schematics-dahlander-diagram.jpg" rel="nofollow - https://www.practicalmachinist.com/vb/attachments/f11/27411d1287940424-220-440v-nameplate-2-speed-motor-changing-voltage-wiring-s-s-contactor-schematics-dahlander-diagram.jpg

I would ASSUME the big 4 wire inlet on the 4x4 junction box on the back, is the 3 phase power INLET....... Then you have a flex cable that goes up to the two AB boxes...So those are probably the 3 phase wires that connect to the 3 contactors in the AB box..

The smaller 3 wires coming out of the 4x4 junction box might be the feed for the table ?  You could open the 4x4 box and look and see what they are connected to...  Since there is only 3 wires, it may be 2 wires of the 3 phase plus the ground... That means you would have 240 single phase going to the table motor ??  That 240 v single phase could also go to the  big toggle switches, and end up being the BLACK wires that turn the electric coils on / off inside the AB boxes..

What is really missing is HOW does the table motor work ?  Is there another DC box that controls it ?  Is the motor AC or DC ?  Is the motor reversable ?  You might want to look at the back of the BIG toggle switches and see how many wires each has... You probably going to have to open each box and start drawing a diagram of where the wires start and go..

i would start by opening the 4 x 4 box and the AB boxes and trying to trace out how the 3 phase inlet wires run up to the AB boxes, and how the two AB box contactors are wired together.... also look at the back of the BIG switches.. how many wires.. etc.

question is WHY was the small 3 wire cable from the 4x4 box cut off ?  I would think that would go to the table motor or its switch ??  why cut it off ?

there has to be another conduit box, or a very sophisticated contactor set on the back of one of  toggle switches to change the motor speed.. several wires would be involved.

Assuming the AB boxes are FWD and REV, then there will be 3 ( 3 phase) wires going into the first box... 6 wires between the boxes.... the 3 wires OUT of the second box toward the motor..  the BLACK wires at the bottom would come from the FWD-REV switch.

Inside the SPINDLE MOTOR electrical box, there will be 4-5 wires from the motor, and the 3 wires coming from the AB box.... Couple of the wires may be jumpered together inside this box... then several of the wires will go to the SPEED SWITCH... if there is no contactor box by the SPEED SWITCH, then the switch will have several terminals on it as it has to connect different wires ( the 4-5 in the motor) together to get the two different speeds.

There is not much else we can do to help without seeing more of the wires and how they are routed.... My wires are colored and yours are green inside the AB box... but they should have a NUMBER tag on each ( normally).. unless the guy just did it one at a time and used a similar print..

EIther way, your going to have to start tracing out wires to determine where they go.... 240 v 3 phase comes in at the LEFT into your 4x4 box.. i left off the GROUND wire (4th) to simplify. .... also i didnt complete the POWER SWITCH or show the TABLE FEED as i dont have enough info on that....a look at the back of the switches might help.

 

Note that in the AB boxes,  my wires between the boxes are Red- Green- Brown on the left and Red- Brown - Green on the right... thats how you get the REVERSE.. change two wires.

I still wonder WHY the Table motor wires (?) were cut ??  If they are in fact that.

EDIT..... OK, you thing the 3 small wires are another INPUT and not an OUTPUT to the table ?  ..... that would not be normal to have TWO POWER cables into the same 4x4 box.

I guess that brings up another question.. If there is 120v single phase power for a LIGHT... did they also use that elsewhere ?  ........ Those two AB boxes have a coil on the bottom that the FWD-REV switch sends power to enengize.( the black wires) ... I assumed that was 240 v single phase from 2 of the 3 three phase wires........ its POSSIBLE they used the 120v light bulb wire to also send power to the F-R switch to send power to the coils..... Need to look CLOSE at where the  3 cut wires run.. ( just the light, or other also).

steve(ill) wrote: It is ILLEGAL to run a 3 phase 240 and a single phase 120 in the same 4x4 power box....

NOT necessarily.  It is bad practice to bring in TWO separately-derived power supply services into the same machine, through the same box, except for circumstance where all power sources are disengaged by a ganged multivoltage switch...

but it is rare for that to happen in MOST tool environments.  The exceptions are usually when the machine has a VERY HIGH voltage input (say... 1200v) for running really large drive motors, but has 120v CNC controls and work lighting.  Basically, if there's a 3-phase 480 input, and a 120v single phase, they'd put a dry transformer across two of the 480 legs to derive that control power from downstream of the 480v safety switch.

The other thing that is generally considered bad practice, is to have a neutral wire on a 3-phase machine... i.e. a 480/277Y feeding into a machine, where the Y centerpoint and one leg is providing 277 single-phase to something, while the 480V 3-phase powers a motor.  It's considered bad practice (because a neutral means there's zero-sequence current (unbalanced 3-phase load) which, if marginal, makes the machine carry the remainder through it's ground wiring... so having a Y-centerpoint (that's 'centrepoint' for our brethren north of the Poutine Curtain) generally doesn't happen in an industrial environment.

The location of the high/low speed Dahlinder switch MIGHT be located INSIDE the mill's column...  with the speed selector shaft protruding to a control handle on the outside of the column.  On my Bridgeport, I tucked the VFD, and a control transformer, inside the BRJ column, and mounted the power, lighting, and speed/direction control pendant feedthrough in a box on the side... it's so nice to have it out of the mayhem...

steve(ill) wrote: ...better to have a 120v PLUG in the wall behind the mill and get your power that way and leave the 240v feed separate into the 4x4 box..

I totally agree there... that's a universally accepted method.

Another common way, was to use a 240:120v control transformer just big enough to run a light... which I've done many times... but..

The other way (which nowdays iseasy) is to use LED worklighting that is powered by a switch-mode power supply that'll accept 100-260vac and run a half-dozen good sized LED modules strategically placed.  I haven't gotten around to changing out some of mine, but the drill has an older 120v LED fixture, and the lathe has an overhead worklight (on a niftly countersprung dentist's worklamp boom!)...

What I've been considering, is running LED strip lighting under the column of the drill and mill... 12v, and distributed over a large area so as to reduce shadowing.  IF/when I do, I'll include pix and report, but I've got many irons in the fire right now...

Please take LOTS of pictures BEFORE you start even moving wires !!

Different angles, with GOOD lighting !!

I had a wire 'magically' come off 'somewhere' in a 'new to me' box.....

... It was not obvious where it had come from..

3 or 4 dayze later I finally figured it out......PITA was one of the nice 4 letters I mumbled...

the three HOT wires will be the ones that run up the conduit to the AB box and connect to the FIRST 3 contacts.....If you get it connected and the motor runs REV when the switch says FWD... then go back to the phase converter or the 4x4 box and just switch 2 of the three wires.