I need to add an e-stop switch to a small milling machine. The motor is a Baldor, rated 1 HP, 115 V, 13.2 A. I'm not familiar with the technicalitie s and advice will be helpful.
One possibility is an Allen Bradley 100-C16DJ10 contactor with a start/e-st op switch on a bracket on the end of the table. The coil on that contactor is 24 VDC and for that a power supply such as A-B Flex I/O 1794-PS13 will be needed. These parts are readily available through eBay.
These are some of my questions.
The motor is easily rewired for 230 V, 6.6 A but changing the service in this institutional setting will be expensive. Is there an argument to chan ge the service?
Is the modular arrangement with the 24 VDC coil and PS advisable? I migh t also hunt for a contactor with a 115 VAC coil. Among the more recent A-B components in eBay, the 24 V coil is commonplace. A multi-decades old Squ are-D contactor with a 115 or 120 VAC coil is easily found. The benefits o f the 24 V coil are silent operation and smaller hazard from the 24 V contr ol circuit? The disadvantage is the need for the 24 V PS.
A contactor and PS will need an enclosure. Best to look for that after t he components are here. Any tips to find something suitable?
Greetings Peter, The advantage of having a 24 volt coil is that the E-stop switch will be switching a low voltage. This means that the wires running to the E-stop switch need less protection than if 115 volts were running through them. Code will require the extra protection. What about the switch that turns on the motor now? Is it switching 115 volts? If so, can the E-stop switch be put into the same housing or can another housing be attached to the existing housing? Will locating the E-stop switch by the other switch be OK? If so there will be no need to run conduit. However, when I have wired E-stop switches on my machines they have always been in places relatively far away from the control panels so I used 24 volt coils in the contactors. As far as changing the service to the motor to 230 volts goes I see no advantage that outweighs the cost. The motor running at 230 volts could use smaller gauge wires and there would be lower losses from resistive heating. So if it were a new installation then it would make sense. But since the wires are already there and contactors capable of handling the higher current when the motor starts are plentiful then there is no reason to change. If you do decide to go with a contactor with a 24 volt coil you should use one that has an AC coil. That way all you need is a small 24 volt control transformer for the coil. 24 volts DC will require more parts, at least a rectifier, that the AC version won't need. Eric
As far as I know, e-stop circuits are usually wired such that the contactor must be energized for the machine to run. In other words, with the e-stop button NOT pushed, the e-stop switch is ON, and the contactor is ENERGIZED. This protects you against open circuits in the control side of the e-stop circuit.
Usually the button is large and red and clearly labeled. If you have other equipment that already has an e-stop button, look at it for examples. The simplest kind of switch is "push to stop, pull to run", but you can also get "push to stop, turn to run" and "push to stop, key to run" types.
If an operator has a choice of places to stand when using the machine, you may have to provide an e-stop button for each operating position. (There are probably rules about how far away the button can be from the operator, but I don't know what they are exactly.) Electrically, this is easy - just wire all the buttons in series.
Use a contactor with a 24 V AC coil. That way all you need is a 120 V (or 240 V) to 24 V transformer, which is cheaper than a DC power supply. If the mill already has a limit switch or other controls, it may even have 24 V AC available already. If not, you can probably get a transformer all packaged up in an enclosure, or get a "bare" transformer and install it in the existing control enclosure. If you think this mill might ever be used on 240 V in its life, you might look for a transformer that has a dual 120 V / 240 V primary. If not, just a 120 V primary is OK.
If you can easily measure the voltage at the motor terminals under load, do so. Clamp down a piece of 2x4, mill it at a decent feed and speed, and check the voltage. (If you're absolutely sure that the chips won't land on your meter probes, you can mill metal, but wood is safer for this.) If it's higher than about 104 V (90% of the 115 V rating), there is probably not much to be done. If it's lower than that, it's worth investigating.
You can check some easy stuff with the power shut off and, if needed, locked out at the building circuit breaker. Start at the motor and work backwards, making sure that all the connections are clean and tight. Screw terminals, push-on terminals, wire nuts, whatever you have. If there is a plug and outlet connection, see if the plug gets warm in operation, and if so, consider installing a new outlet and maybe a new plug. This mill shouldn't be sharing a circuit with anything else, but if it is, see what it would take to correct that.
If the machine is 100 feet (or even 50 feet) from the breaker box, then this won't help much, but: sometimes there is a junction box on the wall near the machine, with a short piece of conduit to the machine. If there's already a splice (wire nuts) in that junction box, it can help a little bit to replace the last few feet of wire from that box to the machine with the next gauge or two heavier wire, as long as that legally fits in the conduit.
That's usually how it works, except with an AC coil on the contactor, and 24 V transformer.
Anything billing itself as a "contactor" should go "clack" or "thunk" when it operates. :)
Yes. You can use thinner cable and string it further around the machine if needed. It still has to be reasonably protected - with conduit if necessary. Make sure it won't catch on the mill table or anything else over the full range of motion of the machine. It's also nice if it doesn't block a great place for the work clamps, chip brush hook, etc.
See if there's room in the existing control box. If not, look for a "NEMA box" at the electrical supply store or online. These start where regular junction boxes leave off and go up as big as you like. There is a number that tells you how well sealed the box is. NEMA 1 is pretty much like a regular junction box. NEMA 12 is a little better. NEMA 4 can stand being hosed off. Take a look at the existing control box to see how well it is sealed.
For a NEMA 1 box, you can just drill holes in the box to mount the transformer, contactor, etc. I'm not sure about NEMA 12. For NEMA 4, drilling holes wrecks the water-tight rating, so usually the box comes with four or more threaded standoffs already welded inside of it. You can get a matching steel plate that bolts down to these standoffs; you can drill whatever holes you want in the plate. You also have to buy NEMA 4 rated strain reliefs or bushings for where the wires go through the side. A NEMA 4 box will probably come with predrilled holes to mount the box, plus prescribed rubber and metal washers to use in those holes.
Note that most NEMA boxes won't come with knockouts or wiring holes; you get to make those yourself. Since you have a mill, this is not a big deal. :)
For the e-stop switch, you can also get boxes that are pre-punched to fit standard industrial pushbuttons. You just specify how many button holes you need, and whether you want metal, plastic, etc.
I am not an electrician and this is not electrical code advice. This is also not advice about complying with OSHA or other regulations.
What is normal practice for a 24 V control circuit? SJO? A cable inside a helical aluminum conduit? Cable in braided copper or steel? Maybe I should be hunting for lower coil voltage, 12 or 6 V.
Yes and reversing. Visible in the photo. Made by GE.
Fitting a contactor inside any of the existing structure is unlikely. Probably mount an enclosure on a bracket on the motor flange at the back. Approximately behind the motor in the photo.
Yes, my preference is a start/e-stop on the front of the table at the right end.
That was my thinking.
An old lathe here has a magnetic switch made by Brook Motors Ltd. It's always buzzing when engaged. The phenomenon is mentioned in the third paragraph here.
No problem. Assembly will be performed or supervised by an electrician.
There is a Square D 9001 BG201 here with start and stop pushbuttons. Start is a n.o. switch and can be connected to energize the coil. Stop is another switch, n.c., and can be connected to break the coil circuit. If power fails or the coil circuit is interrupted in any way, the contactor will open.
Ok, I've seen that type. Probably a more recent design than the BG201. But a BG201 is here and should suffice.
At least I'd prefer a switch on the front of the table at right end. Another mounted on top of the headstock might be appropriate.
No low voltage power is already available on the machine but a small Allen Bradley power adapter isn't expensive on eBay.
If a low voltage adapter is installed, there should be a way to isolate it when the machine isn't in use. The existing switch will serve if the contactor can be connected between that and the motor. Something I might have to investigate.
Helpful tips. Thanks. The wires from the breaker panel to the wall receptacle run about 3 m behind gyprock. The motor is connected to the receptacle with 2 m of
14/3 Type S, black rubber or neoprene outer coat.
The recent model contactors I've seen on eBay all have DC coils. Several are this model or similar.
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Yes but see above about buzzing noise.
Not possible.
OK, thanks. I'll ask the electricians here.
OK, thanks. The BG201 is a complete enclosed unit.
No problem. For specific details there are qualified people here.
Apparently this has been superseded by SJOOW, but it's the same thing - the round black rubber stuff. That works if you don't need much mechanical protection. You can use almost any gauge down to 22 AWG or so, but 18 AWG is probably the smallest commonly available size.
If there is coolant splashing around near the ends of the SJOOW , it's a good idea to use the clamps that put a rubber donut around the cable.
Inside the control box, you can use anything that's suitable for 120 V;
18 AWG is fine. Use stranded wire; it will live longer under the vibration of the machine.
The first upgrade would be plain old EMT electrical conduit (if it doesn't have to move) and something like Type MC armored cable (if it does). The second upgrade is probably liquid-tight flexible conduit (Sealtite or equal) - that gray stuff that you see going from outside air conditioner units to the building. Both MC and liquid-tight cable are ridiculously larger diameter than you need for the wires in an e-stop circuit, but there you go.
24 V is pretty much the standard for industrial stuff.
A NEMA 1 box on a bracket that picks up a couple of the motor flange bolts might work pretty well.
Well... it's a machine shop, not a library. :)
That will work. Usually you need three wires to this kind of switch.
You can wire some more NC pushbuttons in series with the "stop" button on the Square D control if you like.
Depending on how the motor is wired, the action of the switch might be kind of complex; it might not be easy to put the transformer or power supply after the switch.
It sounds like the machine has a plug and a socket at the wall; unplugging the machine probably meets a requirement to isolate all power to it.
You should be in pretty good shape at 120 V with that short of a run. The 14/3 cord to the mill will drop about 0.4 V at the rated load of the motor. Going to 12/3 cord will only improve the drop to about 0.25 V.
These are probably designed for use with a PLC or other computer controls. There's no reason you can't use them in your application, though.
If this place has a facilities department or HVAC person, you might ask them. They may have a contactor on the shelf, or some old equipment you can steal parts from. Of course, filling in the paperwork to transfer it from them to you may be more expensive than buying a new contactor. :)
They should know a good place to get NEMA boxes locally. They may even have a suitable one lying around. It looks like your motor lives up at the top of the machine, relatively away from coolant, chips, etc; a NEMA
1 box may be enough.
Tip: Use a slightly bigger box than you think you need. It's always nice to have more room for bending wires, getting your fingers in there, and so on.
Thanks to all who have replied. I'll start gathering the parts and try to remember to post a follow-up when when finished. Given the low priority, might be a while.
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