Question about NEC

[William Payer]

I am planning on using contactors to turn on/off 220 volts circuits in my shop. The contactors can be had with either 120volt or 24 volt actuating coils. Since the wiring for the actuating circuit needs to be in the same physical electrical box ( separate large electrical box like those used for electrical panels) as the 220 contactor , is having both 24v and 220v (or 120 and 220) in the same space allowed by the NEC? I think the 120 and 220 together may be ok since you find it in a main panel together, but can low voltage be in a box containing 220v circuits?

[Jim Becker]

I cannot answer the NEC question, although I suspect you are right about LV and HV not being permitted to "cohabitate". I wired up the contactor I use to turn my cyclone on and off using 120v to avoid this.

[Mike Cutler]

Short answer is yes. 24VDC relay logic is in use all over the US. It is the interposing, control wiring, for 120, 240, and 3 phase 480.
Allen Bradley, Siemens, Gould, Honeywell, GE, Eaton, Ansul, etc, all have older PLC's that work exactly like you intend. You can buy a stand alone low voltage contractor at any electrical supply house, and pick your output voltage and current ratings.

Unfortunately the longer answer is how you are doing it, and if you're doing it in a code legal manner for residential wiring. It can be done though.

[William Payer]

Thanks Mike.

I have two separate uses for the contactors. First, my intentions are to have all my 220 and 120 outlet circuits near tools to be turned off/on via a single switch(with a lock) for safety purposes when I am not there. For this I would most likely use a standard 120volt circuit to do this. (contactors would be in another large electrical box next to the panel, making the wiring easier.

Second use is to be able to turn my dust collector on/off from each and every tool station. For this I would employ 24 volt wiring as it has fewer restrictions on boxes, running locations, etc. I intend to use 3 way and 4 way switches (much like wiring a light to be controlled from 3 or more locations). Flipping the switch at any single tool station would toggle the DC from off to on , or vice versa.

[Mike Cutler]

William

The first use could be solved with a mechanical disconnect. The second with a wireless signal. RF, IR, etc. You would have the controller/remote with you wherever you are to turn the DC on and off. They make these as complete units.

120vac interposing relays and contractors are very common. A lot of larger machines have them built in. You are looking at a somewhat expensive solution, but entirely doable. It's a very common protection scheme in industrial applications.

It almost seems as if a simple mechanical disconnect is all you might need. Put the machines and duplex receptacles on one panel with a mechanical disconnect, and have the lighting off a separate panel. But, you know more what you need to effect than I do.

[Jim Becker]

The second with a wireless signal. RF, IR, etc. You would have the controller/remote with you wherever you are to turn the DC on and off. They make these as complete units.

The "complete" wireless DC controllers are fine for small dust collection units, but fail early and often for those of us who have larger systems. That's why I chose to go the contactor route with mine...safety and reliability. That said, one can combine the two, using the low cost wireless controls to actuate a 120v control circuit for the heavy contactor that in turn supplies power to the DC. Me...I chose a single, centrally located standard wall switch to control my contactor. It never breaks and never needs batteries...can't lose it in a pocket or in some sawdust, either, since it's mounted "in" the wall. D

[Mike Cutler]

Jim

I know that I personally would lose the remote in a New York minute. I don't even own a TV, so keeping track of a remote would not be for me.

I get to work on some really slick protection schemes at work. It's a shame that they're so expensive, because they really would be nice for a home wood shop setup.

[Ole Anderson]

I have my tiny remote connected to a big red lanyard like you hang on your neck with a nametag. No, I don't hang it on my neck.

[Nick deMolitor]

I'll jump in as well with a vote for using a a mechanical disconnect. I plan on doing something similar. Run 100A to shop panel A, that has lights and a few plugs off it. Come out of panel A to a Disconnect mounted high on the wall that could be locked off then back to another 100A Panel we'll call Panel B, with the power for all the big tools. (Because I know what I was like as a kid) As for the Contractor for the DC, my plan is to use a 120v coil, contractor to keep it simple.

Sorry I only know CEC not the NEC but this might point you in the right direction. So if you want to use 24v you can, only the insulation rating has to be equal to or higher then the highest voltage (to ground) in the box. Here in canada anyway LVT is rated at 30V, avg house wiring is 300V if I recall. So technically just use 300V rated jumpers when your in the contractor box and your fine with LVT outside.

[Anthony Whitesell]

I guess I'll jump in as well. The interesting point is that the contactor design isn't as subject to the NEC as it is to UL508A, Design and Construction of Industrial Control Panels. UL508A leans heavily on the NEC but also contains all of the requirements for component size and labeling. I was also just recalled, working on a panel such as this while live voltages greater than 50V are present is also against the NEC without wearing specific safety gear.

I do like the contactor design, but think a 100A breaker in the main to a mechanical disconnect to 100A distribution subpanel is the most sure fire, robust, longest lasting method (contactors do eventually wear out either the coil or the contacts).

[Jim Becker]

Jim

I know that I personally would lose the remote in a New York minute. I don't even own a TV, so keeping track of a remote would not be for me.

I get to work on some really slick protection schemes at work. It's a shame that they're so expensive, because they really would be nice for a home wood shop setup.

One of the main reasons I wanted to bag the portable remote is that it was never where I actually thought it was when it was time to turn on the cyclone...that wall switch doesn't move!

[Andy Booth]

24VDC as a control voltage is reasonably safe and is preferred for buttons and switches near people.
You will need a 24 VDC power supply. And fuses to protect the PS.

Color code is important here. NFPA79 specifies Blue for 24VDC and Black for all AC voltages >50VAC. White can be used for AC neutral.
AC and DC wires can touch provided both wires are rated for the application.
Use minimum 300V stranded wire for the DC. The rating must be printed on the wire.
As a general rule minimize areas where DC and AC wires lay together and do not place AC/DC in the same conduit.
I like DC to be 18Gg MTW. MTW is much more flexible than THHN. The 18 ga is not for ampacity, it is for mechanical strength.

UL508 does govern panel layout and include requirements for wire radius, spacing and cooling. Required in many industrial installations.
Do not place any control devices in a home/commercial circuit breaker panel. They are not rated for this.
Include a disconnecting means (a circuit break counts) upstream of the contactor panel. This allows you to remove all live voltages when you work on the panel.
While there are rules, I prefer to think of it as common sense.

If this is near dust, use a NEMA12 panel, and keep it closed. Dust buildup in a panel like this can be hazardous as it is the wood flour that gets through the smallest of cracks.
Spend time laying out the panel and pay attention to adequate wire space. Use wire duct to help keep everything neat. Inadequate wire radius and space is the most common issue I see in panels.

You may want to consider solid state relays (SSR) as they do not spark.
Use MOV's for arc suppression to make the contactors/SSR last longer (Look up flyback protection on the web)
Disconnect both poles for 220V and just one pole (hot side) for 120V.

I will often include 24VDC LED's as indicators for what is turned on.
If you are feeling flush consider using a current switch to automatically turn on the dust collector anytime you turn on a power tool.

Create a schematic, use wire numbers and build to print.
Workmanship counts. Give each connection a firm tug after you tighten the screw.
This is not rocket science, but it does need planning and some knowledge.

I often use automationdirect.com for many of my projects and have never had a problem. You will save quite a bit of money.

I have also been considering using Solid state relay's for remote on/off control of a dust collector as most of the commercial stuff is light duty.

These are just guidelines and every application is different. Your mileage may vary and so on. Have fun.

Andy

[Curt Harms]

The "complete" wireless DC controllers are fine for small dust collection units, but fail early and often for those of us who have larger systems. That's why I chose to go the contactor route with mine...safety and reliability. That said, one can combine the two, using the low cost wireless controls to actuate a 120v control circuit for the heavy contactor that in turn supplies power to the DC. Me...I chose a single, centrally located standard wall switch to control my contactor. It never breaks and never needs batteries...can't lose it in a pocket or in some sawdust, either, since it's mounted "in" the wall. D

I did about the same. I have a single D.C. switch centrally located. If someone wanted to get fancy, it's not too hard to have multiple low voltage start/stop switches. People have used inexpensive remotes to switch the control circuit of a contactor. The advantage over the all-in-one dust collector wireless controllers is that one can use a more substantial contactor. I'm happy with a 'real' switch. No stray RF activating the dust collector when we're not home, never lose the remote, the heavy duty contactor is very unlikely to fail.

[Lee Schierer]

I cannot answer the NEC question, although I suspect you are right about LV and HV not being permitted to "cohabitate". I wired up the contactor I use to turn my cyclone on and off using 120v to avoid this.

Jim, where I used to work we built machines and also their control panels. We often had low voltage and high voltage in the same cabinet. If the low voltage is coing in from a separate source then you would have a dual power situation and would need to label the box as having two power sources. But if the low voltage is coming off the same power input, then there shouldn't be a problem.

[Jim Becker]

Lee, didn't the LV and HV have to still be "separated" in that cabinet? Perhaps the rules are different "within" the machines as opposed to in the wall.