branching a 110 off of a 220 20 amp circuit

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Old 09-30-16, 07:47 AM
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branching a 110 off of a 220 20 amp circuit

I'm wiring a large woodworking shop. Panel is a Homeline 200 amp 40/80 fed by the outside meter with a main circuit shut off. I've installed the panel inside the basement, removed the green ground screw and added grounding bars bonded to the box. Neutral is now floating. Most of my machines are 220 20 amp. I'm running separate circuits to each machine.

Questions:
If I run 12/3 to the 220 outlet can I branch a 110 outlet by taking one hot and the neutral? I would be using a table saw on the 220 and an area light on the 110. Would this create the light flicker?
If this isn't advisable can the 220 outlet be wired with 12/2? In the panel white becomes hot and the ground goes to the bonded ground bar or the floating neutral? Or do I need to use 12/3? If so how do I wire?
 
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Old 09-30-16, 08:44 AM
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Use the 12/3. That is referred to as a multiwire branch circuit. It can provide line to line loads and also line to neutral loads. Be sure to use a double pole common trip breaker because of the 240V line to line loads. The startup of the saw will most likely cause the light to dim momentarily.
 
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Old 09-30-16, 11:14 AM
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I don't think you can pull 120V for other use off of a 240V circuit, the circuit is dedicated to the machine.
A MWBC to me is sharing a neutral for Two 120V circuits, not a 240 plus 120.
 
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Old 09-30-16, 11:46 AM
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I don't think you can pull 120V for other use off of a 240V circuit, the circuit is dedicated to the machine.
A MWBC to me is sharing a neutral for Two 120V circuits, not a 240 plus 120.
Not a problem if circuit is 20A or less with using a common trip 2P breaker. OP stated 20A circuit.

See NEC 210.4(C) Exception #2. This is why I said the need to use a common trip 2P breaker.

Above 20A you run into outlet amp size restrictions, ie. can't put 20A outlet on a 30A circuit.
 
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Old 09-30-16, 11:48 AM
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You can use the 12/3 method to power the light if you want, however there could be a couple problems. If the saw trips the breaker, the light will go out and generally you don't want to lose lighting when a blade is spinning. The light will dim when the saw starts up or bogs down.

I'd consider an upgrade to #10 for the table saw, even if it only requires 20A. TS motors usually benefit from a bit of extra copper during startup, and with the #12 you're limited practically to about 2-3HP.
 
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Old 09-30-16, 02:34 PM
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Thanks for the education guys.
It'd be a dream come true if you could pull 120V off of a Range circuit to power a microwave hood, but I can see the difference in this situation.
 
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Old 10-01-16, 06:55 AM
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Thanks for the sound advice. I've decided to run separate 220 circuits to each machine and two 110 circuits with 6 outlets each.

Questions :

Can I use 12/2 for the 220 outlets making both the black and white wire hot? Since the oulet boxes will be exposed I'm using metal boxes secured to an 8x10 post. Do I attached the ground wire to the metal box and the bonded ground bar in the panel?

I'm a newbie to electral work and this forum. Apologies for bad terminology or simple questions.
 
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Old 10-01-16, 08:23 AM
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Terminology: It is 120v and 240v not 110 and 220v.
Can I use 12/2 for the 220 outlets making both the black and white wire hot?
This is why it is important to fill out your location in your profile. Please do that. if you are in the U.S. yes. The white can be relabeled any color but green or gray. bands of black tape are okay. If you are in Canada no. You must use Red Romex.
Do I attached the ground wire to the metal box and the bonded ground bar in the panel?
Yes.
 
 

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