Combine 2 existing 110v circuits for 110/220?

Just bought a lathe that looks like it will require a 1-2 hp 220 VFD. The breaker panel in the shop is full, but not over capacity as I tend to only use one device at a time, plus a few residuals. I have 2 options I can think of to get power to it

1. Tap into existing overhead run to table saw. This is a little complicated as a it involves cutting into conduit, pulling slack and the wire is all phase taped Thhn, so I have to trace each wire (3 hots, 1 neutral, 2 grounds)

2. I have a quad box on the wall that is in a good place and has separated circuits for each side. I did this during installation to have matched numbers of outlets. Either side has 110v outlets on that sides respective circuits.

Can I safely combine the circuits in that box, tie those 2 breakers together and still run the 110v outlets on the rest of the circuit? My logic says yes, it isn't any different than a 4 wire dryer or multi branch setup.

I am probably going to run 4 wire to the lathe anyway and add a plug box for coolant pumps, lights or other accessories

not an electrician here, but when my sparky wired my shop we did several 14/3 circuits that are run to a split duplex receptacle and a 240 receptacle. both legs have to be on a double breaker.
code in your area could be different, but here it was OK to do

The breaker in the panel that serves those two combined circuits for 240V needs to be a double pole common trip breaker because of being used for a Line-to-Line load. Don't use a handle tie on two single pole breakers because that will be independent trip which is okay on a multiwire branch circuit serving just Line-to-Neutral loads.

We do something similar where I work doing Trade show electric. We use 3 phase 120/ 208v power and have boxes with both 3, 120v receptacles and 1, 208v 20a recpt. in the same box. The 208v plug is supplied by 2 of the 3 available phases so it is possible to use both voltage types at the same time as long as you don't overload the panel breaker. You could put a 220v plug on one side of your double box and a 20a duplex next to it with the hot jumper tab removed to get both voltages out of one box as long as your 2 hot phases are not on the same phase at the breaker panel.

Perfect. Just need to pick up a double breaker, unless I have one in the spares box.

Now I just have to figure out everything I need to wire the vfd, but that will wait till the lathe gets here

You cannot use phase tape to mark neutrals & grounding conductors smaller then 4 AWG, and all 120 volt receptacles in shops, garages, & outbuildings require GFCI protection, with no exceptions. Need to check code on some other issues. What NEC edition is GA on?

norcal said:

. What nec edition is ga on?

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2014 nec

alfredeneuman said:

2014 nec

Click to expand...

Thanks, saves me the trouble of looking it up.