Adding a 3/4-wire 220v receptacle

Question

I've got two 220V appliances I'm trying to add a receptacle for. I've got a dual-pole 25A breaker, and am completely replacing the existing outlet.

My issue is that one appliance has a standard NEMA 6-15 plug, and the other just has a four-wire pigtail. I'm trying to figure out how to wire them both up.

For the four-wire appliance, it looks like the NEMA 14-20 is the correct plug to attach to it. It should only draw 6 amps-- is there a lower-rated four-conductor plug I should use?

As for the receptacle, my understanding is the 6-15 doesn't use the neutral wire. Can I run 4 wires to a junction box and then have two outlets-- a 6-15 and a 14-20-- with the neutral only going to the 14-20?

Am I doing something terribly wrong or dangerous? This doesn't seem too complicated, but I've heard enough horror stories to be cautious.

EDIT:

The appliances are a table saw (13 amp draw) and a dust collector (6 amp draw). There's not room in the breaker box for another set of breakers, so I was hoping to get both on the same circuit. But it sounds like it's a better option to separate them?

The wiring diagram for the dust collector doesn't help me much-- it can be wired for 230V or 460V operation and details how to change that, but never specifies what the four leads are for. They're standard colors (black, red, white, green).

The existing breaker is two 25A breakers with their handles attached. Each connects between neutral and a different hot side in the box. I went with 25A over 20A just because the draw from both appliances is 19A and that didn't seem like a lot of room in case one draws a bit more on startup.

Answer 1

Because you selected a 25A breaker, you will need to use 10AWG wire for the branch circuit.

NEC has a table of which receptacles are permitted on which sizes (amperages) of circuit. Nothing in the NEC authorizes any kind of receptacle on a 25A breaker. It will exceed the capacity of a 20A receptacle. A 30A receptacle will allow plugging in things which draw more than 25A. No receptacle will work. As such, all loads will need to be hard-wired.

An additional rule says that if the sum of all hard-wired loads exceed 50% of the total circuit ampacity, then no receptacles are allowed on that circuit.

I have no earthly idea why you bought a 25A breaker. But when I was first learning, I bought a stack of 30A 1-pole breakers reasoning that surely they must have a use - and then I never found one, except for a TT30 RV connector. So welcome to the club.

Normally on a circuit of ampacity X, all sockets on that circuit must be of ampacity X.

On a 30A circuit, there can be any number of receptacles, but they all must be 30A.

A 20A circuit can have any mix of 15A or 20A receptacles, unless there is only one socket, and then it must be 20A. This is due to a special exception in Code, you cannot mix-and-match socket sizes otherwise.

If I were you, I would take back the 25A breaker and get a 30, then 10AWG wire to (daisy chained) a 14-30 and 6-30 receptacle, modify both cords to have a -30 socket on it, and done.

I wouldn't try to make it work on a 20A receptacle, you're overamped - the dust collector is a continuous load so 6A * 1.25 derate = 7.5A + 13A saw = 20.5A -- too much for a 20A breaker.

Actually, if I were you...

I would take back the 25A breaker... and get the gear to put a subpanel in the wood shop. My motivating factor would be the shortage of space in your main panel.

• a 60A breaker
• 4AWG Al wire /3 with ground
• A subpanel of good quality, e.g. Siemens, CH, QO etc. with 20 or more spaces. I don't care the ampacity of the subpanel as long as it's >=60. It needs a main breaker if it's in an outbuilding.
• Ground bar accessory kit (any respectable panel will come with this)
• two 20A/240V breakers for that subpanel type
• 20A/120V breakers as desired
• A bit of 12/2 and 12/3 wire (or THHN if in conduit)
• A NEMA 6-20 duplex socket (can be 6-15 if duplex)
• A NEMA 14-20 socket
• NEMA 5-15 or 5-20 sockets as desired
• Necessary boxes, conduit, etc.

The 6-15/20 duplex receptacle is for the saw and whatever else. The 14-20 single (they don't come in duplex) is for the dust collector. 14-20 is a common receptacle type, 14-15 exists but nobody stocks it. The common-as-dirt 5-15s or 5-20s are for all your 120V tools. I assume you already have a circuit coming in to supply those, serve it out of this subpanel. Pro tip: leave the lighting served out of the main panel, that way if you trip the subpanel breaker the lights do not go out.