Converting 120VAC garage circuit to 240VAC/120VAC "dual" circuit

[Robbie Lee]

I read an old thread here that I thought was going to clarify this issue, but, alas, it managed to lose me at some point.

Please picture a detached garage containing three 120VAC duplex receptacles. The power for these receptacles comes out of the ground, through the exterior wall (into the garage itself), up the wall (through conduit) and into a steel single hub gang box. After disabling both of the garage breakers, the NEMA 5-20 duplex receptacle was removed from said gang box to reveal a maze of wiring; hence, the word "hub." In short, there a (3) 12 AWG solid copper wires and (1) 12 AWG stranded wire running into this box, which I will refer to as REC A – Black (BLK), Brown (BRN), White (COM) and Green (GND) stranded. NOTE: There is no bare ground wire coming into this box.

As one faces REC A, there is a section of conduit coming out of the left side of the box, which runs straight into another steel single gang box. Pulling the NEMA 5-20 duplex receptacle out of this box, which I will refer to as REC B, reveals (2) 12 AWG solid copper wires and (1) 12 AWG stranded wire – BLK, COM & GND.

As one faces REC A, there is a section of conduit coming out of the top of the box, which runs up the wall, into the open trusses in the garage "ceiling" and into a third steel single gang box, which I will refer to as REC C. Pulling the NEMA 5-20 receptacle out of REC C reveals (3) 12 AWG wires – BLK, COM & BARE COPPER. NOTE: All three wires run out of REC C and into an overhead lighting fixture.

At this point, I'd like to point out that REC A & REC B are protected by a 120V/20A breaker, while REC C (and the rest of the overhead circuit) is protected by another 120V/20A breaker – and BOTH breakers are tied together by a metal jumper/link.

As the owner of this garage is low on cash and needs to convert both REC A & REC B to supply 240V NEMA 6-20 receptacles – to facilitate paying carpentry work – the idea is to employ the BLK wire and the BRN wire as HI wires for REC A, and, as REC B is already wired to the hub, the BLK and the COM wires running between REC A (the hub) & REC B will automatically provide 240V for a second NEMA 6-20 receptacle.

At this point, all seems fairly clear to me. The problem comes in when I'm asked about how to best supply the overhead circuit, which supplies the NEMA 5-20 receptacle and the overhead lighting with 120VAC. I've known the owner of the garage in question my whole life and, yes, I gave him all the obligatory warnings and advice about installing a separate 120V circuit for the overhead devices, but he simply doesn't have the cash for it. Despite my advice, I know that he's going to use what he has on hand, so I'd like to make this "economy conversion" as safe as it possibly can be.

My idea was to attach the BLK wire – which is already running up to REC C – to the top screw on the new NEMA 6-20R and into a economical (small) sub breaker panel containing one 120V/20A breaker – which will be installed between REC A (the hub) and REC C (overhead). The COM wire will pass directly through REC A and be attached to the COM bar in said sub panel. Not to state the obvious, but the BLK, the COM and the BARE leads/wires will continue on up to the 120V overhead circuit.

Although I retired from the electrical field, I'm not a licensed electrician. I'm a childhood friend of the guy asking [me] for advice, though, so I thought I'd ask the forum board for constructive thoughts about my idea before offering any final advice. If I could be there myself, I would. I'm out of state, however, so it's nearly impossible right now. By the way, I'm very interested in why the electrician tied the two 120V/20A breakers – presently supplying the garage – together with a metal link/jumper.

Thanks very much for your time,
Rob Lee

[Jim German]

Well, I can't imagine that it would be anywhere close to being to code, but it seems to me like it should work. I don't see the point in the extra breaker though, a short in the overhead circuit should still cause the main panel breaker to trip, and since the breakers are already linked it should trip the whole circuit.
Also probably not the safest thing to do in the world.

[Jeff Ramsey]

Ask Julie Moriarty this, or invite her to respond to your thread. She's an electrician.

[Charles Lent]

It looks to me like 240 volts may already be available at REC A, but you will need a volt meter to know for sure. The black and brown wires would most likely be 240 volts. Either the black or the brown to the white wire should be 120 volts.
If your volt meter shows this to be true you are in business. The breaker with the handles tied together that is feeding the garage is controlling both the brown and the black wire. If either wire experiences an overload this circuit breaker will trip both circuits. This is necessary when protecting a 240 volt circuit, even if part of this circuit is also supplying 120 volts outlets or lighting.

Think of the white wire as the center tap between the black and the brown wire (which it is). 240 volts between black and brown and 120 volts from black to white and 120 volts from brown to white. The white wire is considered as Neutral and the black and brown are the two hot wires. The stranded wire appears to be ground and should be colored with green tape to indicate this. Checking with the volt meter between either black or brown and the stranded wire should show 120 volts if this stranded wire is indeed connected to ground.

Once you have proven that all of the voltage measurements above are correct you can begin rewiring. For the 240 volt circuits you will need the black, the brown, and the green. For the 120 volt circuits you can use either the black or the brown, the white and the green. I strongly recommend that you maintain the correct colored wires and actually remove the white wire from the outlets that will become 240 volt and only have the black, brown and green wires in these boxes. If you leave the white wire do not use it. Put a wire nut over the end to insulate it. Now install the correct 240 volt outlets. There are several versions available. DO NOT use the old 120 volt outlets to supply 240 volt power. If you do somebody will surely make a mistake and plug a 120 volt tool into 240 volt power. It will surely destroy the tool and it might kill them too.

Charley

[Robbie Lee]

Thanks for the kind replies, folks ...

Charley: The black (HI) lead/wire I wrote about presently passes directly through REC A (the hub receptacle), passes through a section of conduit and ends up supplying the NEMA 5-20 (120V) receptacle mounted to the roof trusses. In other words, it's presently the sole HI wire for the overhead circuit. My idea was to use the black (HI) I just described and the brown (HI) that's presently supplying 120V to REC A and REC B to provide 240V to the same boxes (REC A & REC B). As the black wire will, obviously, have to supply half of the 240V, the black wire would have to be connected to the both the bottom and the top of one side of the new NEMA 6-20 (240V) receptacle in REC A. The black wire connected to the top of the new 240V receptacle will continue up, through the conduit, until it reaches the proposed sub breaker panel. In other words, the black lead/wire will supply half of the 240V circuit and all of the voltage for the 120V (overhead) circuit. By the way, I've been very careful about which receptacles to install. The NEMA 5-20R (120V) and the NEMA 6-20R (240V) have distinct differences that will not allow erroneous "cross use."

[David L Morse]

It sounds like what you have is a multiwire branch circuit. Google it. I think you will find that having both 240V and 120V loads is NEC compliant. Ganged breakers (or preferably a dual breaker) is a code requirement for a MWBC

You do not need the extra breaker.

I assume that your wiring description is meant to be a diagram and not a wiring method and that you will make all connections inside REC A with wirenuts and pigtail to the 6-20 in REC A.

Two issues are the lack of GFCI and the lights going out with a tool caused overload but you have that now so adding the 240V connections has no impact on the already existing safety situation.

I think your plan, minus the extra breaker, should be fine.

[Robbie Lee]

It sounds like what you have is a multiwire branch circuit. Google it. I think you will find that having both 240V and 120V loads is NEC compliant. Ganged breakers (or preferably a dual breaker) is a code requirement for a MWBC

You do not need the extra breaker.

I assume that your wiring description is meant to be a diagram and not a wiring method and that you will make all connections inside REC A with wirenuts and pigtail to the 6-20 in REC A.

Two issues are the lack of GFCI and the lights going out with a tool caused overload but you have that now so adding the 240V connections has no impact on the already existing safety situation.

I think your plan, minus the extra breaker, should be fine.

Yes, David, I was thinking that the shared common in the existing garage circuit was the reason for the link/jumper. In other words, if there's a short at one receptacle, both breakers must "trip" open to prevent return current flow. Thank you for confirming this.

Your thoughts about my description are right on, as well. Any splicing will be done via wire nuts and tape, but I was thinking about simply using the screws/terminals on the receptacles themselves for powering additional items. For example, I was going to advise removing the white (COM) lead/wire between REC A and REC B, pulling a piece of brown (HI) wire through the conduit and connecting the ends of this new lead to the same end and side of both NEMA 6-20 receptacles. As for the overhead "truss circuit," I was thinking that connecting the black (HI) that already supplies that circuit to the top screw/terminal of the new NEMA 6-20 receptacle in REC A -- on the side being supplied by the black phase. In short, I'm assuming that the receptacles are still designed to be installed in "series," so to speak, with other electrical devices, if needed and/or desired.

Thanks again for your thoughtful post.

[David L Morse]

Most 6-20 receptacles have a single outlet and one screw each side. 6-20r in duplex format with two screws per side is available but you won't find it at a BORG and wouldn't like the price if you did.

Even if you do use a duplex receptacle you'll still need to pigtail what you call the "Black" side since there are three wires that need to connect there: the feed from the main panel, the send to REC B and the send to REC C.

Also, unless you already have the replacement wire, there's no need to pull out the white wire connecting REC A and REC B. Just use paint or electrical tape to clearly indicate that it is no longer a grounded conductor. Any color other than White or Green will do.

[Robbie Lee]

Most 6-20 receptacles have a single outlet and one screw each side. 6-20r in duplex format with two screws per side is available but you won't find it at a BORG and wouldn't like the price if you did.

Even if you do use a duplex receptacle you'll still need to pigtail what you call the "Black" side since there are three wires that need to connect there: the feed from the main panel, the send to REC B and the send to REC C.

Also, unless you already have the replacement wire, there's no need to pull out the white wire connecting REC A and REC B. Just use paint or electrical tape to clearly indicate that it is no longer a grounded conductor. Any color other than White or Green will do.

As I previously mentioned, David, I can't be there to help with this particular project. As a way of contributing, I've already sent a pair of Leviton 6-20 (16462-HI) receptacles back home. Your words about replacing the wire are well taken and, yes, any necessary splicing will be done with wire nuts and tape. Coming from an electronics background, I prefer the use of ferrule rings, solder and heat shrink, but the "perfectionist" won't be there, once again ... so the project environment should be relatively calm and peaceful. ;) Thanks, once again.

[Robbie Lee]

....but you won't find it at a BORG and wouldn't like the price if you did.

I took me a while to piece it together, David, but I really like it ... BORG = Big Orange Retail Giant.

Very Nice,
Rob