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In my garage I ran two separate 20 amp 120v lines, each to its own receptacle, each coming from one leg of my breaker box. I did this so I can run my table saw and dust collector at the same time. They are next to each other in the wall. I have a third unused 15A in the garage as well, where a refrigerator used to be.

I just received a free $1400 table saw that's 240v 12A. Am I able to make an adapter for the NEMA power cord (15A) that will split the 3 wires into two 120v plugs? For one plug, I will run a hot and a neutral and the other plug just the hot. This will give me 2 hots, one from each side of the breaker box, and a single neutral.

I know this isn't ideal, and ideally you would have a single breaker that would trip, killing both legs. But, if it did pull too much current from one leg, that would trip the overloaded breaker.

Please tell me how crazy I am. breaker panel

enter image description here

manassehkatz-Moving 2 Codidact
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Steve Warton
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  • You can't do exactly as you're thinking, but you probably have some options. What's the wiring method here? Conduit, NM, or something else? And do the two circuits in question share a neutral (making it an MWBC)? A picture of your breaker panel would be helpful too. – Nate S. Nov 12 '19 at 00:21
  • This is an attached garage, so I just ran the two 12/2 wires through the wall into the garage. The big problem is I did this over 10 years ago, and a few years ago finished our basement with drywall on the walls and ceilings, including the room that has the breaker panel. I have no way of running new wiring out there, which would have been easy (maybe a small subpanel with then 240v and 120v off of it). It looks to be a single neutral. There's one "metallic" braided line coming into the panel, but two neutral "poles", one on each side. – Steve Warton Nov 12 '19 at 00:32
  • Well, that's a bit of a problem since you can't have the two hots be in two different cables for 240V use. How would you feel about converting one of your existing 120V-only circuits to instead be 240V-only? – Nate S. Nov 12 '19 at 00:41
  • Consider using your former fridge circuit for this -- you'd only need to swap the current 1 pole breaker for a 15A 2 pole, and swap the NEMA 5-15 receptacle with a NEMA 6-15, and mark the white wire with some colored tape on both ends -- perfectly standard, safe, and code legal. – Nate S. Nov 12 '19 at 00:44
  • Ah, well the full breaker box is a completely different problem, which you should probably have included in your question. There are probably ways to solve that, but you'll definitely need to post a pic of your panel in that case. – Nate S. Nov 12 '19 at 00:47
  • Since you want 240V in the location of the two 20A circuits, would it work for you to convert one of those two to 240V-only? So you'd have 1 20A 240 circuit + 1 20A 120V circuit in that location? If that works, it's the same procedure as above, except use a two-pole 20A breaker, and a NEMA 6-20. – Nate S. Nov 12 '19 at 00:49
  • https://i.ibb.co/WPZtv1L/breaker.jpg – Steve Warton Nov 12 '19 at 00:58
  • I goofed. That 15 amp dedicated isn't dedicated. I just remembered. That would have been too easy. The arrows show the location of the two 20A I ran into the garage. Yeah, as far apart as possible! I guess what I could do is in the top left where there are two old-school large 240v breakers, is buy two smaller 240v breakers. Put the well pump (dual 20A) back into a newer, smaller dual, and then remove the bottom left 20A breaker, move the wire up top and use that with another new 20A dual 240v breaker. Hmmmm...Whatcha think? – Steve Warton Nov 12 '19 at 01:00
  • Yes, that could work, though note that you need 'quad' breakers for this. See here for more details: https://diy.stackexchange.com/questions/110151/what-is-a-tandem-breaker-aka-duplex-cheater-twin-double-stuff-etc/110152#110152 – Nate S. Nov 12 '19 at 01:04
  • Do you need GFCI breakers for this? If your location has adopted the latest NEC code, you probably do, and they don't come in double-stuff size, so that may force you to rearrange things further, and/or install a subpanel (which I'd recommend doing anyway -- your panel is overfull already). – Nate S. Nov 12 '19 at 01:06
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    Just how averse are you to having to rework some drywall? Also, can you post more detailed photos of your breaker box please? – ThreePhaseEel Nov 12 '19 at 01:09
  • For a really off-the-wall solution, consider transformers. Take 240 v at the main panel, step it up to 480, send it down one of those dedicated 12/2 cables, and step back down to 240 in the garage. Feed it into a subpanel there. (That table saw wasn't really free, was it? ;-) ) – Greg Hill Nov 12 '19 at 01:14
  • https://i.ibb.co/QX4m9cP/breaker.jpg – Steve Warton Nov 12 '19 at 01:38
  • So is the reason for a quad breaker so that each leg of the 240v gets power from each side of the box? – Steve Warton Nov 12 '19 at 01:40
  • @SteveWarton both circuits need access to both legs of power, yes. Can you post a photo of the big label on the inside of the door to your breaker box, please? That would help us confirm that your panel can indeed use double-stuff/quad breakers in all positions, and a few other things as well – ThreePhaseEel Nov 13 '19 at 01:34

1 Answers1

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Don't hokey-doke this thing when it's so easy to do it right.

You already have the right wires in the wall

You already have a dedicated circuit for your table saw. I presume you don't plan on running both saws at the same time. So we'll simply convert the dedicated table saw line to 240V and we're done.

Let's talk about the difference between a 240V circuit and a 120/240V circuit. A 240V circuit has 2 hots and a safety ground. A 120/240V circuit has 2 hots, neutral and a safety ground, and is able to power both 240V and 120V parts of the machine - such as a dryer's motor/timer or an oven's light.

A table saw will need 240V power. It has no use for neutral.

Convert the 120V saw circuit to 240V

The cable is converted from hot-neutral to hot-hot simply by marking the white wire with black tape to redesignate it a hot.

Now, it must be punched down onto a circuit breaker.

We could do some very difficult rearranging of panel space. However there's an easier way. There is a 20A 2-pole breaker in the left side center. We'll replace that with a 20/20 tied quadplex. Possibly a Siemens (ITE) Q22020CT2, which provides two tied 2-pole 20A breakers.

  • The inner breakers are tied and also are common-trip. I don't know what that existing 20A breaker serves, but it might need common trip. So we place that on the inner.
  • The outer breakers are tied, but do not guarantee common trip (they do promise common maintenance shutoff). They are suitable for this saw.

So for this saw circuit, remove the hot from the old saw breaker, and its partner former neutral (the one now marked with black tape). Both those go on the two (outer) hots on the new breaker.

By the way, whoever runted all your hots and neutrals to barely enough length to reach the breakers they're on now.... don't invite them back. Every hot and neutral should be long enough to reach every breaker space in the panel.

Harper - Reinstate Monica
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  • Harper, I REALLY appreciate you taking your free time to answer this and help me out. You made it very clear. Thanks! Also, so I don't have to go downstairs and rip the cover off and take a breaker out, is that the exact quadplex I need for my box? Thanks again! – Steve Warton Nov 12 '19 at 04:32
  • @SteveWarton your breaker box is a Siemens I take it? (the label on the inside of the door will say) – ThreePhaseEel Nov 12 '19 at 04:53
  • @SteveWarton ThreePhaseEel will know exactly what you need for sure, just put up the info off your panel door label (A photo will do). Mine was only a guess based on your breakers and ignoring CTL. – Harper - Reinstate Monica Nov 12 '19 at 15:54