[rickinnocal]

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

 

[rickinnocal]

...The 120V loads go from either hot to ground...

Don't you mean from either hot to neutral?

...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.

Yes, that was what I was planning.

Richard

 

[rickinnocal]

A MWBC is used to get 2 120 volt circuits, not for both a 120 and a 240. If it is used for a 120/240 volt circuit it is not a MWBC

Electrically it would work but I can't believe it would be compliant.

Since I seemed to be getting conflicting answers, I googled some more, and found a site that discusses the NEC itself. (Thank you AllenJ for providing the proper name for this circuit so I knew 'what' to Google!)

A MWBC can indeed provide both 240 and 120, so long as the fault protection is correct. On a MWBC providing only 'out of phase' 120V service, that can be 'either' a double pole breaker or two single pole breakers with a handle tie. The NEC requires that a double pole breaker be used if the MWBC also provides 240V service.

Additional....
The googling also came up with a number of sites with arguments 'against' MWBC's, some saying that future editions of the Code should ban them completely. However, from reading the logic behind the argument it seemed to me that the objections are met by properly installed fault protection, and that the same potential exists within the panel box itself on 'any' pair of out of phase circuits if one circuit loses neutral continuity. After all, tracing them back, every circuit in the house is on a common neutral in the box.

Richard