Hey guys,

This should be pretty a pretty straight forward question. I'm currently laying out components and wiring a control box for one of my projects in the shop and I'm wondering how safe it is to pull 110v from a 4 wire 220v circuit. The basic idea is the box has multiple components inside, some have switchable inputs but one does not, it requires an 110v input. The box has a dedicated 220 4 wire circuit so would it be safe to pull from one leg of the circuit from within the box? Thanks in advance!

 

Welcome to AAC
4-wire is L1, L2, Com (grounded) and Ground(green). For 110, you need either of the L's, Com (white), and Ground (green). The L's are commonly black, red, or blue, but code allows almost any color except green and white. In a specific area that is wired for 110, I like to use the same L1 or L2 as in the area, if current requirements are not exceeded. I don't believe that is code, and I know of instances when one purposely uses both L's in the same area.

 

I'm wondering how safe it is to pull 110v from a 4 wire 220v circuit.

What is the nature of the 220v circuit and also what demand does the 120v require, usually as long as the current demand does not exceed the 240v supply and it is properly protected, fused etc, then there could be no problem.
Max.

 

What is the nature of the 220v circuit and also what demand does the 120v require, usually as long as the current demand does not exceed the 240v supply and it is properly protected, fused etc, then there could be no problem.
Max.

Thanks for the reply,

The 220v circuit powers two DC power supplies, one with a rated output of 72v 10a and the other with a rated output of 12v 30a. The 110 input is .8a with a rated output of (V1) 5vdc 2.2a and (V2) 24vdc 1.0a. This is a control box for a CNC Machine. I have wired 110 by the control box if needed but I would rather do as much inside the box as possible. The 220 circuit is on 10g wire with a 30 amp beaker.

 

For a single machine with 220 and 110, I would definitely use the same L, i.e., L1 or L2 for all 110's, particularly if there are low voltage circuits. There can be significant voltage differentials between the L's, common, and ground.

I worked in a lab that had split 3-phase for 3-phase (rarely needed), "220," and "110." Fortunately, the 110V sockets were color coded red, black, and blue. It was a disaster to plug an instrument into a blue color socket and the millivolt recorder (circa 1970's) into any other color.

 

For a single machine with 220 and 110, I would definitely use the same L, i.e., L1 or L2 for all 110's, particularly if there are low voltage circuits. There can be significant voltage differentials between the L's, common, and ground.

I worked in a lab that had split 3-phase for 3-phase (rarely needed), "220," and "110." Fortunately, the 110V sockets were color coded red, black, and blue. It was a disaster to plug an instrument into a blue color socket and the millivolt recorder (circa 1970's) into any other color.

Thank you very much! I could see where that would be a nightmare.

 

If you have to ask then you don't know what you are doing. This isn't a project where you can afford to make mistakes. Hire a qualified electrician to make these changes for you.

 

If you have to ask then you don't know what you are doing. This isn't a project where you can afford to make mistakes. Hire a qualified electrician to make these changes for you.

Clearly I don’t want to make any mistakes hence why I wired 110 next to the box in case I couldn’t safely do this. As I don’t claim to be an electrical engineer or anything similar that’s why I asked a group of people who are. I didn’t see any reason why I couldn’t do what I asked as it’s essentially the same as pulling from the breaker box. I don’t believe I will spend who knows how much money to hire someone to run a 12 inch wire for me when I can safely do it myself. I appreciate your advocation of safety as a huge advocate of safety myself, thanks for your response.

 

Don't trust your life or the safety of your home for anonymous advice on the internet that could also be misinterpreted A mistake could easily cost you many, many times whatever the cost to run that wire by a pro would cost.

 

It is unfortunate to live in such fear as to be paralyzed!!
The simple approach is to use a volt meter to first verify which wire is the neutral line, and then find which wire is a 110 volt line. "4-wires could be 240+neutral + ground, OR it could be three-phase plus neutral, or it could be that strange system that I have come across, 3-phase with two lines at 120 volts and a teaser phase at 220 above neutral, with 220 between each of three phase legs. So without doing a meter observation or looking in the distribution panel it is quite poorly advised to make any pronouncements, given that there is NO Statement that it is wired to any particular standard.
Careful probing with a voltmeter is the simple way to discover the answer as to which setup it is.

 

It is unfortunate to live in such fear as to be paralyzed!!
The simple approach is to use a volt meter to first verify which wire is the neutral line, and then find which wire is a 110 volt line. "4-wires could be 240+neutral + ground, OR it could be three-phase plus neutral, or it could be that strange system that I have come across, 3-phase with two lines at 120 volts and a teaser phase at 220 above neutral, with 220 between each of three phase legs. So without doing a meter observation or looking in the distribution panel it is quite poorly advised to make any pronouncements, given that there is NO Statement that it is wired to any particular standard.
Careful probing with a voltmeter is the simple way to discover the answer as to which setup it is.

Thanks for your reply,
Given as I wired the entire building myself, I know for certain the circuit is wired as two 110s a neutral and ground. Both legs have been measured with a multimeter and are within 4 volts of each other.

 

I don't see any reason why you can't do that inside the equipment box - its pretty common.
I'd balance the load by running each power supply off separate 120V legs hot-neutral. Fuse or add a circuit breaker the 120V input of each supply appropriately so that you don't have to rely on the double pole 220V breaker to trip. The result is no different than pulling a 120V single pole circuit through a breaker in a distribution panel if I understand your question.

Good luck and welcome to AAC.

PS It sounds like you know what you're about. We do have to be careful sometimes in the advice we give if it seems like the member could hurt himself - or others.

 

This is a control box for a CNC Machine. I have wired 110 by the control box if needed but I would rather do as much inside the box as possible. The 220 circuit is on 10g wire with a 30 amp beaker.

Normally you would take the four conductors to the machine (CNC) enclosure which would have a local disconnect switch and all the necessary fusing.
For some more info on enclosure wiring, the NFPA79 is useful, a copy is out there in PDF I believe, if not I could send one.
Max.

 

I don't see any reason why you can't do that inside the equipment box - its pretty common.
I'd balance the load by running each power supply off separate 120V legs hot-neutral. Fuse or add a circuit breaker the 120V input of each supply appropriately so that you don't have to rely on the double pole 220V breaker to trip. The result is no different than pulling a 120V single pole circuit through a breaker in a distribution panel if I understand your question.

Good luck and welcome to AAC.

PS It sounds like you know what you're about. We do have to be careful sometimes in the advice we give if it seems like the member could hurt himself - or others.

Thanks, that’s the kind of information I was looking for! I was wondering about imbalance issues. I understand completely some people don’t have any business with anything electrical and you guys need to be very cautious with your answers.

 

Also If you have a 120v-N -120v supply and two separate 120v loads from each of the L1 and L2 conductors to a single N conductor, the current in the neutral is the Difference Between the loads and not the Sum.
Max.

 

Normally you would take the four conductors to the machine (CNC) enclosure which would have a local disconnect switch and all the necessary fusing.
For some more info on enclosure wiring, the NFPA79 is useful, a copy is out there in PDF I believe, if not I could send one.
Max.

That’s exactly how I have this configured, the disconnect is on the enclosure. That’s the biggest reason I wanted to convert inside the enclosure instead of adding a second disconnect for the 110. I’ll see if I can find a pdf of NFPA79. Thanks or the information!

 

Thanks for your reply,
Given as I wired the entire building myself, I know for certain the circuit is wired as two 110s a neutral and ground. Both legs have been measured with a multimeter and are within 4 volts of each other.

OK, I had not realized that you had that big advantage of knowing how the place was wired, I never have that benefit, making my efforts a lot more interesting. The only potential issue might possibly be if you were using both at the same time. But probably that should not be a big concern.