[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

 

[Saturday Cowboy]

u must have/use 4 wire.

 

[mpoulton]

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.

 

[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

 

[mpoulton]

Don't you mean from either hot to neutral?

Yeah, I can't believe I wrote that. Edited.

 

[AllanJ]

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.

 

[rjniles]

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.

 

[AllanJ]

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

 

[a7ecorsair]

You cannot use the existing 3 wire dryer circuit to add a sub panel as it requires 4 wires.

In the opening post:

In the garage at the moment is one 220V outlet, four prong, for a dryer.

 

[rjniles]

My answers in red

Hmmm. Didn't he say that the original existing dryer receptacle was 4 prong ergo fed with 4 conductor cable?

Missed that Allan.With a 4 wire he can add a sub- panel to replace the existing dryer receptacle.

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?

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 MWNC

 

[a7ecorsair]

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.

 

[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

 

[rjniles]

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.



Richard

I would like to see the reference where you found this.

 

[HouseHelper]

Section 210.4 (C) Exception 2. Basically says you may use a MWBC for line to line loads IF you protect the circuit with a common trip double pole breaker.

 

[rjniles]

Section 210.4 (C) Exception 2. Basically says you may use a MWBC for line to line loads IF you protect the circuit with a common trip double pole breaker.

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.

 

[mpoulton]

I would like to see the reference where you found this.

The NEC is generally restrictive, not permissive. If something is not prohibited by the code, it is allowed. Note that HouseHelper did find a provision that specifically addresses this, though.

 

[HouseHelper]

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.

I am a "working electrician" and this is definitely allowed... this is no different than a dryer or range circuit, which is a 120/240V MWBC!

 

[The Deez]

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.

 

[Scott3229]

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.

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....

 

[The Deez]

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....

Agreed, I've only been a licensed electrician for about 10 years. All i have to go by is past experience, and i can honestly say that I haven't done this, nor would i do it and I can think of LOTS of times I had the opportunity to do this wiring method. If it was me and in my opinion i would just run a 12/2 for the 120v stuff and leave the 240v stuff on a dedicated circuit. This is an interesting topic though, I have a meeting with a state inspector tomorrow in Boston for a job, I'm gonna run this by him and see what his opinion is. Maybe he can reveal a secret code article.