Adding two 120v outlets to 20amp 240v circuit
I want to add two 120v/20amp outlets (separate circuits) on the outside of my house. I have some code questions.
The closest circuits/panel are my workshop circuits that are fed from a sub-panel in my basement workshop. Presently, my bandsaw is supplied by a 240v/20amp breaker (i.e. both pole switches tied together) using a 12/3 wire (black, red, white with ground) to a box on a first floor joist (in the basement overhead) before going to another box with the bandsaw’s 240v/20amp outlet.
I can put a larger box in the overhead (to prevent an overfill violation) and run a new, additional 12/3 wire to feed a new outside box with two 20amp GFCI outlets (using two separate pigtails to the common neutral/white wire). I would also keep the 240v/20amp breaker (that has the two pole switches tied together) and the 240v outlet that powers the bandsaw.
Alternatively, I have two 120v/20amp breakers adjacent and on separate poles (in the same sub-panel as the bandsaw circuit) that also feed a box in the overhead before going to the two GFCI outlets by the workbench. These also use a 12/3 wire using the black to one outlet, the red to the other (separate circuits) and two pigtails from the single neutral to both GFCI outlets. These separate breakers do NOT have their switches tied together. I’d rather not use this circuit to ensure I can use the full power to the workbench outlets while also using the new outside outlets.
The question is what does code say about using a 240v/20amp circuit powering a single tool outlet and connecting that circuit to two additional 120v/20amp GFCI outlets on the separate poles/circuits? Additionally, does the present code require the three wire/two 120v circuit (separate breakers/poles) to my workbench have their switches connected so the power to the whole circuit (12/3 wire) is shut off when either one is tripped or turned off? Or, is just marking the labels on these two circuits in the load center as sharing a common neutral (white) wire acceptable? This was what was signed off by the county inspector when first done around 2004.
Thanks in advance!
Replies
This is fine as long as the two poles of the breaker are ganged together.
Sounds fine as long as it uses the ganged 2-pole breaker, as you describe, so that if either load trips the breaker both are disconnected. It's call a multiwire branch circuit (MWBC). The GFCI doesn't make a difference from that perspective.
On the load side of the GFI the circuits need separate neutrals.
Roger that. I'm not going to have any outlets downstream from the two I install. There will be no wires on the load side of the GFCI outlets.
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jayohaetchenn: Appreciate your answer. Should I replace the other breakers with two-pole (240v/20A) breaker on the other MWBCs or am I grandfathered since the sub-panel was already inspected and passed?
If it were mine, I would put a double-pole breaker on any existing MWBC that doesn't already have it. It's a pretty slim chance, but theoretically one leg could trip and the other could stay on, which could then pass current back through the common neutral and present a hazard. Hardly something to drop everything and go fix, but next time you're at the store a $12 breaker seems a fair price to do it right. Also watch out for aftermarket handle ties, which aren't a great alternative to internal "common trip" breakers: https://inspectapedia.com/electric/Circuit-Breaker-Handle-Ties.php
Thanks and stay well and safe!