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220V & 110V outlets

10K views 21 replies 10 participants last post by  mpoulton 
#1 ·
Hello, everyone.

I'm wiring up some receptacles in my new garage workshop, and have some questions.

I have one tool - a radial arm saw - that is 220V / 7A. All my other power tools are 110V. As a hobbyist, obviously I'd only ever be running one tool at a time, although my dust collector - 110V / 5A - would be running whenever any of my 'dusty' tools was.

In the garage at the moment is one 220V outlet, four prong, for a dryer. It is connected to a 30A double pole breaker. We are buying a gas dryer, so will not be using it for a dryer.

My plan, subject to the opinion of the experts here, is to replace the 220V outlet with a box, and run hard conduit from that around the wall to where I want my outlets. I'm going to drop three or four receptacle boxes from that, each with 2 x 110V & 1 x 220V outlet in it. That will give me flexibility to move tools later as I see what layout works.

Here's the electrical question....

1) Is it acceptable to provide the 110V to the outlets by using one of the two hot legs of the 220V, or do I need to pull a three conductor wire for the 110V in addition to the wire for the 220V outlet?

2) Since the RAS has only a three-pin plug, Hot-A, Hot-B and Ground, is there any reason to even pull 4-conductor wire for the 220V if I pull separate wire for the 110V? Obviously if I can use one of the hot legs of the 220V for my 110V then I have to pull four conductor because I need the common neutral, but if I can'y can I just use three conductor wire for both?

Thanks for your help,

Richard
 
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#3 · (Edited)
You can do this, but you'll need to replace the 30A breaker with a 20A. You can run four wires: two hots, neutral, and ground. The 120V loads go from either hot to neutral, and the 240V receptacles (make sure to use a 240V receptacle type!) go between the two hots. I installed a few circuits like this in my old shop (not re-using an old circuit, though). The way I arranged it, I installed double gang boxes. Each box had one duplex receptacle, and one 240V 20A receptacle. The duplex was split so the top half was on one hot and the bottom was on the other. That way I could run two high-current 120V tools from the same outlet.
 
#6 ·
YOu can run 3 conductors (hot, hot, ground) to an outlet box with nothing but a 240 volt only receptacle in it.

If you run the feed to a new subpanel, you can keep the 30 amp breaker at the main panel. The subpanel would have double wide double breakers for any 240 volt circuits and any circuits where two hots (on opposite sides of the line) share a neutral.
 
#7 ·
Is this garage a detached structure from the house? Or is it attached? The answer to that question makes all the difference in the world.

Assuming it is attached: You can not use a single circuit to provide both 120 & 240 volt receptacles without a sub panel. You cannot use the existing 3 wire dryer circuit to add a sub panel as it requires 4 wires. What you could do is use the existing dryer circuit to provide a 240 volt circuit for your saw. Change the breaker to a 15 or 20 amp double pole. Run a new 12-2 cable from the breaker panel to install the 120 volt receptacles.

If the garage is detached, ignore what I have said above.
 
#8 · (Edited)
You cannot use the existing 3 wire dryer circuit to add a sub panel as it requires 4 wires. What you could do is use the existing dryer circuit to provide a 240 volt circuit for your saw. Change the breaker to a 15 or 20 amp double pole. .
Hmmm. Didn't he say that the original existing dryer receptacle was 4 prong ergo fed with 4 conductor cable?

The saw, meanwhile, was 240 volt only with 3 prong plug (one ground prong).

Hmmm. You mean you can't run a traditional MWBC* (a 120/240 volt circuit) to a box with a 240 volt receptacle and a (or a pair of) 120 volt receptacle in it?

Multiwire branch circuit
 
#11 ·
Here's the electrical question....

1) Is it acceptable to provide the 110V to the outlets by using one of the two hot legs of the 220V, or do I need to pull a three conductor wire for the 110V in addition to the wire for the 220V outlet?

2) Since the RAS has only a three-pin plug, Hot-A, Hot-B and Ground, is there any reason to even pull 4-conductor wire for the 220V if I pull separate wire for the 110V? Obviously if I can use one of the hot legs of the 220V for my 110V then I have to pull four conductor because I need the common neutral, but if I can'y can I just use three conductor wire for both?

Thanks for your help,

Richard
Need a joed or JV or brric or somebody to comment:
The OP whats to feed a two gang box as a MWBC with a split 120 volt receptacle and then tap the two hots for a 240 receptacle.

Electrically it would work but I can't believe it would be compliant.
 
#15 ·
I have reread that exception and exception #1 about 3 or 4 times and do not believe the intent is to allow the use of multiple line to neutral and line to line loads on the same MWBC. Maybe we need input from one or more of the working electricians on this forum.
 
#18 ·
here it is straight from the nec

210.4(C)
Line-to-Neutral Loads. Multiwire branch circuits
shall supply only line-to-neutral loads.

Exception No. 1: A multiwire branch circuit that supplies
only one utilization equipment.

Exception No. 2: Where all ungrounded conductors of the
multiwire branch circuit are opened simultaneously by the
branch-circuit overcurrent device.
 
#19 ·
This section to me has been a topic of confusion more than once, but im leaning in the direction that you MAY do this as long as they are the same amperage, and have a simultaneous disconnecting device, thinking logically, if EITHER of the two legs exceed amperage, it will trip both legs, and on the other end if you need to shut of either of the circuits for service, you will be forced to shut off both to eliminate the hazards of neutrals....
 
#21 ·
I'd opt for a sub-panel to replace the dryer outlet. Then one could run 120 Volt circuits for the standard receptacles, and a separate 240 Volt circuit for the radial arm saw. Separate breakers for each circuit.
 
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