Questions About 110V Circuits Off Of 220V Circuit

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Old 12-31-11, 02:49 AM
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Questions About 110V Circuits Off Of 220V Circuit

I tried posting this message once and it appeared not to work. So I am trying again. If two such messages eventually appear, my apologies.

I have done a fair amount of DIY residential wiring, but there are still things I do not know.

Many years ago my father-in-law, now gone, who was an electrician, put in for me a 20A two-pole breaker in the service panel to establish a 220V circuit for a 220V outlet for a radial saw. He also split off of the black hot wire in the 4 conductor wire (hot black, hot red, neutral white, bare ground) which he used for the 220V circuit to establish 2 - 110V circuits. One goes to a switched light above the saw and one goes to an electrical outlet now used for TV, phone, vacuum cleaner, etc. I recently added a second electrical outlet to the circuit by simply taking off from the first outlet. The second outlet is being used for a jointer/planer which draws up to 15 amps. The switched light circuit and the branch circuit supplying the two outlets both come off the black hot wire of the 220V circuit, but at separate splice points. The red hot wire in the 220V circuit is not currently being used for 110V lines. The 110V circuits have ground wires and use the white neutral in the 4 conductor wire used for the 220V circuit. They use 12-2/g Romex.

I now have reason to want to establish yet another 110V branch circuit off this 220V line to create a separate outlet for a 15A table saw. And I wonder if I can do that by using the red hot wire.

The radial saw and the jointer-planer can actually be on at the same time now without tripping the 20A two-pole breaker. Even though the jointer-planer uses up to 15A the radial saw on 220V uses, I believe, only 6A (actually 5.5A; 11A if it were wired for 110V). The table saw also uses up to 15A. So I wonder if I could actually have all three pieces of equipment running at the same time without tripping the 20A two-pole breaker.

Is there any problem with establishing another 110V circuit off the red hot wire in the 220V line and using the same white neutral and bare ground wire as the current 110V circuits branched from the black hot wire do? I assume it would NOT be wise to try to establish another outlet for a 15A table saw using the black hot wire again.
 

Last edited by bob821; 12-31-11 at 05:12 AM.
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Old 12-31-11, 05:08 AM
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Welcome to the forums! Although you didn't specifically say, I am assuming this is in an attached garage set up in a sub panel. If so, you can replace the subpanel with one that has the capacity of introducing 120 volt breakers for your 120 volt circuits. Can you open the box up and take a picture of the inside so we can see what you have? http://www.doityourself.com/forum/el...your-post.html
 
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Old 12-31-11, 05:35 AM
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Larry, I think the OP is just dealing with a MWBC, and not a 240 circuit based on the circuit descriptions.

To Op, are any of the receptacles different than a regular receptacle in your house?
 
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Old 12-31-11, 05:41 AM
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Actually, no. This is all in a basement where the main electrical service panel for the house is located. The 220V circuit comes off that. There is an unused 15A single pole breaker in this panel, and there are other sources of 110V circuits in the basement that are not overused and could be added to. It is 200A service. But the 220V 4-conductor wire passes through a junction box where the 2-outlet-110V-circuit branches off the black hot wire of the 220V circuit). This junction box is attached to a floor joist (Romex is run through floor joist) very near the stud/plaster board wall in the basement in which I wish to have another 110V outlet for the table saw. In other words, if I can take off the red hot wire in the 220 circuit the run would be short and easy to do. I would take off of this junction box. I also think, perhaps wrongly that this 20A 220V circuit, which for years supplied only a radial saw drawing 6A, a 100W light bulb above it drawing less than 1A, and an outlet facing the "rathskeller" side of the basement, mainly used for a cordless phone and for a TV, has been underutilized. I have added one 110V outlet for a 15A jointer. I now wonder whether I can get another 110V outlet for a 15A table saw off the other hot wire.
 
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Old 12-31-11, 06:02 AM
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I believe what you have is a multi-wire branch circuit. This is where two hot legs share a common neutral. A 240 volt circuit would share the black and red on the same receptacle.
 
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Old 12-31-11, 06:16 AM
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The receptacle for the radial arm saw (RAS) is a 220V receptacle, very different from an ordinary 110V outlet. The white neutral wire in the 4-conductor cable going to this outlet is simply capped with a wire nut and not used for this outlet. Of course it is used for the 110V branch circuits that come off the black hot wire of the 4-conductor cable. Both the red and black hot wires are attached to the 220V outlet (receptacle). And the bare copper ground wire is also attached to this receptacle, of course. The plug on the original cord coming from the RAS was changed also, by my father-in-law, and the saw motor itself is rigged to run on 220V based on the operating manual for the saw. It can be rigged to run on either 110 or 220. I do not know what the acronym "MWBC" stands for.
 
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Old 12-31-11, 06:29 AM
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MWBC = multi-wire branch circuit. I explained this in post #5.

Thank you for confirming the circuit identity as a true 240 volt circuit. In essence you are using the circuit as a 240 and as a MWBC.

I like Larrys idea of the subpanel with proper 120 volt circuits, not sharing a 240.
 
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Old 12-31-11, 06:55 AM
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Wouldn't it be cheaper and easier just to use a different 110V circuit in the basement than to establish a sub panel for one additional 110V outlet? I know I could get this additional 110V outlet from another 110V circuit, or even establish a new 110V circuit from an unused 15A breaker in the service panel. It would just be cheaper and easier to make the short run from the nearby 4 conductor cable that supplies the 220V outlet.

Is there anything theoretically wrong with doing this, i.e., with taking off of the red hot wire for another 110V circuit when 110V circuits already exist off the black hot wire? I wonder if the white neutral wire serves only as a neutral for the black wire based on how it is attached to the 20A two-pole breaker, or whether it can serve as a neutral for the red hot wire as well. I haven't looked inside the service panel yet. I suppose I could just check with a volt-ammeter or a simple circuit testing light to see if the red hot wire will make a circuit with the white neutral, right?
 

Last edited by bob821; 12-31-11 at 07:23 AM.
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Old 12-31-11, 07:30 AM
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I also like Larry's idea of a small panel. A six circuit panel would only cost about $30

While not ideal, taping off one leg of the 240 volt circuit is acceptable as long as the same wire size is used. Your circuit breaker will protect the branch circuit.

If possible, I suggest wiring the lights on a separate circuit then the Multiwire circuit running your machines. That way if you do trip the breaker you will not be left in the dark with spinning blades winding down.
 
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Old 12-31-11, 07:37 AM
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I can't see anything wrong with your plan but it certainly would not be my first choice. I would have run a new circuit for the 12o circuits and left the 240 circuit alone.
 
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Old 12-31-11, 08:56 AM
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Fortunately there are 3 other overhead lights on 2 other circuits in the workshop area. The light directly above the RAS is just the closest. So, even if the 220 circuit breaker tripped I would not be in the dark.

The wiring, including that in the 110V lines is all at least 12 gauge based on the 20A breakers.
 
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Old 12-31-11, 10:50 AM
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Based on what I’m reading, I believe you should establish a new circuit, or stop using all equipment at the same time. If you are running a shop—where all equipment is being used consecutively, then you should think about installing a small sub-panel to handle the demand loads. Seems to me, you are trying to do too much on one circuit. Just my one cents
 
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Old 12-31-11, 12:51 PM
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I am a hobbyist "woodworker" only. Retired. Former biology professor, teacher, research scientist. No commercial enterprise involved here. No employees using multiple machines at the same time. No professional woodworking shop. The truth is that I typically only use one machine at a time. But I found it interesting that if a neighbor or friend came over and wanted to use the radial saw while I was using the jointer it apparently would not trip the breaker. Besides the jointer, radial saw, and newer table saw, I also have other machines, such as a router table, a scroll saw, and a thickness planer. Also hand-held power tools, like drills, sanders, etc. They all use other circuitry than this 220V line.
 
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Old 12-31-11, 01:37 PM
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The OP is in the basement with the main service panel. I don't see a reason to add another sub panel unless the distance from the main was quite far. I would go for adding another circuit from the panel. I think I would just run 12/2 over to your radial arm saw and remove it from the circuit with the two 120v circuits. That way your 240v is off on its own.

You never know what will happen in your home shop. I don't plan on having anyone else in my shop, but I put all my machines on their own circuits. Very unlikely I will operate them at the same time, but you never know! It's good to be prepared.
 
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Old 01-01-12, 02:43 AM
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I believed/still believe that the 220V line was being underutilized. It is, in some sense at least, equivalent to 2 - 20A 110V circuits, at least it takes up the space in the main panel of such circuits. That means to me that it has roughly as much potential to drive machines as the two actual other 110V circuits (one is 20A, one is 15A) that supply other machines in this "shop" area. Yet for years the 220V circuit powered only the RAS (5.5A on 220V) and a single light bulb, a cordless phone, and a TV set (on the 110V lines derived from the 220V line). So I wanted to use the potential.

I do not want to have to rewire the RAS to work on 110V. So I do not want to eliminate the 220V outlet. But the RAS is the only machine in the "shop" that uses 220V. By adding a 110V outlet for the 15A jointer I felt that I used some of the otherwise unused potential of this 220V line. But it seems to me that there is more potential yet to be tapped.

I have read this thread involving MWBCs:

How Many Circuits on One Neutral - Page 2

It seems that the common white neutral in this case would work with a new red-hot-wire-based 110V circuit. It is a neutral after all and should work with either hot wire. And it seems it would NOT carry additional current and become overloaded. Because of the 180 degree difference in AC phase of the red and black hot wires which are part of the 220V line (to the best of my knowledge they must be this way for the 220V outlet to work at all, and they come from adjacent breaker sites in the panel because they arise from a two-pole breaker), a red-wire-based 110V circuit using the same white neutral would sum with the always-cyclically-opposite-in-charge black-wire-based 110V circuit and the common white neutral would never carry more current than either the black or red 110V circuit was using. Putting it another way, the currents in the red-wire-based and the black-wire-based 110V circuits would tend to cancel each other, not add up to a greater current in the neutral white. That is what the thread cited above seems to indicate. Is that in fact correct? If so, it sounds safe to me.

Furthermore, if one ever did want 3 machines running at the same time (RAS - 11A on 110V but only 5.5A on 220V, plus jointer - 15A on 110V, plus table saw - 15A on 110V) then it seems to me that it would not be possible on two separate 20A - 110V circuits. But, to the best of my knowledge, using the 220V outlet for the RAS would likely make it possible.

I reason that the 5.5A on 220V for the RAS is shared between the two breakers, so that 15A for one of the other two machines plus 5.5/2=2.75A on each breaker for the RAS means less than 20A total on each breaker with all three machines running. Is this reasoning incorrect? Should I be counting 5.5A on *each* breaker? I know already that the RAS and the jointer (used with a 110V outlet tied into the black hot wire in the 220V line) will run at the same time without tripping the 20A two-pole breaker for the 220V line. If there is then 15A from the jointer and 5.5A from the RAS on one 20A breaker then one might have expected it to trip. No?

My local code is the same as NEC. To the best of my knowledge this would still be up to NEC code and safe. Is that incorrect?

In short, I don't see how this would potentially overload the 220V circuit, only tap its unused potential. I suppose I am miserly by nature and hate to "waste" the unused potential. But perhaps I am wrong about the amount of unused potential available. I am open to explanation.
 

Last edited by bob821; 01-01-12 at 04:17 AM.
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Old 01-01-12, 06:03 AM
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Sounds like you now have a good understanding of both your setup and how MWBCs are used.
 
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Old 01-02-12, 05:21 AM
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I have communicated by e-mail with a local electrician, one who some years ago upgraded my electrical service to 200A. He finds no problem with establishing a new 110V line off the red wire in the 220V line and using the common neutral. He also confirmed that the neutral will only carry the balance of the loads on the red and black 110V circuits. He also implied that it will not violate local code since he offered to do it, at a price of course. The one thing about which he cautions is that any loose connection to the common neutral might result in something he calls "wild-phasing," which could potentially destroy machines. However, I don't anticipate any problems with loose connections in the rather simple connections involved. It simply means tying into an existing nearby junction box in which 2 red wires (one from the breaker and one going to the 220V receptacle) and 3 white wires (an unused one from the 220V receptacle, one going to the main panel, and one for the black-wire-based 110V branch circuit), are already connected with wire nuts. I will be sure to use a red wire nut on the four 12g white wires that will be connected, and a red wire nut also for the 2 red/1 black wires involved. I believe that would be an acceptable size in both cases. No? And I will be sure to twist the wires tightly together first. And I will even add electrical tape to help to keep the wire nuts in place, something my father-in-law believed was a total waste of time. The only other connections are on the 20A-rated duplex 110V receptacle itself and I have wired many receptacles in the past without any loose connections I can remember. And the bare grounds on each end, of course.

So I feel that I can do this myself and I think I may be doing it soon unless I hear back with any dire warnings.
 

Last edited by bob821; 01-02-12 at 05:45 AM.
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Old 01-02-12, 01:23 PM
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Thanks very much for all the input. I put the new outlet in today. It seems to be working fine. I twice tried turning on all three machines, with overhead light on, with cordless phone plugged in, and with TV on. No tripping of the 2-pole breaker. I am now going to push my luck by adding another overhead light to be located directly over the table saw. This will just be added to the existing overhead light over the RAS and both will be switched on together. The run is only about 6-7 feet. This will be on the black-wire 110V circuit.

I suppose it may very well be that the breaker would trip if one or more machines were actually being used for sawing or planing while other motors were running. I presume motors might draw more amps under those circumstances. And I haven't tested that. Also if they were simultaneously started by three people. But I do not anticipate that latter circumstance ever happening.
 
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Old 01-03-12, 07:45 PM
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I don't see any code problem with what you installed. Glad to hear the project turned out well.

The motors will draw more current as they bog down under load, so there's a good chance the breaker would trip in the middle of the cut when you have multiple machines running.

Just because the breaker doesn't trip isn't necessarily a good indication of the circuit being within safe capacity. Breakers are mechanical devices and they have a fair amount of variability in when they actually trip, so you have to consider the breaker tripping as one factor in determining whether a circuit is overloaded. You should also add up the amps of the tools, lights, etc running at the same time to make sure it's a reasonable amount for a 20A circuit.

Your description of a one-man shop leads me to believe it won't ever be a problem, but you don't want to push it with the neighbor coming over and possibly tripping the lights out during a cut. I run a dust collector and a similar lineup of tools to yours in my own shop on a 20A MWBC, but my lighting is separate.

Enjoy the sawdust.
 
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