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I would like to connect a jointer to my dryer receptacle but I am concerned about proper grounding. The jointer draws 8.5 amps at 230V and has a NEMA 6-15 plug. The dryer is plugged into a pre-1996 NEC circuit with three wires (red, black and white) and a NEMA 10-30 receptacle. Can I connect the jointer, which uses a green equipment grounding wire, to the dryer circuit which grounds the frame (equipment grounding) to the neutral circuit conductor (white wire)? In other words will the white wire properly ground my jointer if I connect the jointer’s green wire to the dryer’s white wire? I have made a (3 wire) extension cord with a NEMA 6-16 receptacle on one end and a NEMA 10-30 plug on the other end. I have no confusion about where the 2 hot wires go and which is the grounded or grounding blades on the plugs.

  • Is this circuit fed directly from the main panel, or from a subpanel? Also, do you still care about being able to plug in a dryer here? – ThreePhaseEel Dec 27 '16 at 23:14
  • If it is fed from the main panel the neutral and ground will be bonded (I believe that is what ThreePhaseEl is suggesting). – Ed Beal Dec 27 '16 at 23:49
  • Yes, I want to be able to alternate using the receptacle for the dryer and jointer. The dryer's circuit is from the main service panel. There's NM 10/3 with ground from the NEMA10-30 receptacle halfway back to the panel where it enters a metal junction box. There is MC from there back to the service panel. Inside the box the NM's ground wire is fastened to the green screw and the MC is fastened to the box with a connector. Does this constitute a good ground path if all connections are solid? – Tyler Dec 28 '16 at 12:59
  • I believe the Joiner will be safer than the dryer. The joiner is a 240v load and the neutral going back to the main panel is grounded so the only use it will see is a short to ground. Most driers have 120V motors and sometimes controls that use the neutral as a return path with the dryer frame bonded this can create a hazard and that is why code was changed to the 4 wire system. If you change the outlet make sure to run a new wire back to the panel a 3 wire system connected is no safer and possibly more hazardous when connected to a 4 wire outlet without the correct conductors. – Ed Beal Dec 28 '16 at 14:17
  • "If you change the outlet make sure to run a new wire back to the panel..." do you mean run a new ground wire back to the panel? – Tyler Dec 28 '16 at 16:34
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First, remove that NEMA 10 from the wall with great authority and conviction, and strike it many times with a sledge. Set the resulting fragments on fire. Spread the ashes on the pitch of your town's rival football team while screaming "Demons begone!!"

Convert to NEMA 6

Now here's the illegal part. Get some green tape and wrap it around the white wire, on the insulation near the end. Do this on both ends. (it is illegal to mark colored wires as grounds, with an exception for very large wires).

While you're in the service panel, move the wire from the neutral to the ground bus. (On a MAIN panel, they may be the same thing). You have now redesignated the white wire as ground.

You are now wired for NEMA 6. Put a 6-20 receptacle on the wall and replace the 30A breaker with 20A. Done.

Or, convert to NEMA 14 by adding a ground wire

This is 100% legal. Get some 10 AWG bare or green wire (single conductor, solid or stranded). Run it from the connector site back to either:

  • the panel from which this circuit is served, or
  • any junction box that has a 10 AWG or larger ground wire running back to that same panel. I.E. your water heater, stove, A/C etc. This has to be a ground wire, not a neutral wire.

If you pull your NEMA 10 off the wall and discover there's already an honest-to-gosh actual ground wire tucked back unused, awesome! Just pop the cover off the service panel and make sure it's actually connected.

Neutral is not ground

All of my advice will fail you if you believe that Neutral and Ground are just two flavors of the same thing. They are not. They serve completely different purposes. Crossing those purposes gets people electrocuted, which is why NEMA 10 is a bad connector. In the 1950s when they wanted to start grounding things, NFPA very foolishly made a compromise with appliance manufacturers, who were afraid appliance sales would go ice-cold if NEMA 14 upgrade was required everytime you bought a new dryer. They compromised at allowing NEMA 10 to continue in service, and use the neutral as ground. The reasoning was an appliance failure (hot-chassis fault electrifying chassis) was more likely than a connector failure (neutral failure guaranteeing chassis is electrified even on a good appliance). Their reasoning was that NEMA 10 circuits serve large appliances which are rarely ever moved or unplugged. Didya catch that part?

Plugging a 15A appliance into a 30A receptacle

You're not allowed to. The issue is overcurrent protection (fusing).

NEMA 6 follows the exact same rules as the old familiar NEMA 5, because the rules do not specify voltage. Any number of NEMA 5-15 receptacles can go on a 15A breaker. Due to a special exception, any number of 5-15 or 5-20 receptacles can go on a 20A breaker. Same rules apply to NEMA 6-15 and 6-20.

A 30A breaker can only feed a 30A receptacle.

So, changing the appliance cord to 30A is right out.

If you must build a 6-30/14-30 to 6-15 cheater cord, it needs to include overcurrent protection (fusing) at 15A or 20A. If you use 20A, you might as well use a 6-20 receptacle, since 6-15 plugs go into it. All the wiring up to the fuse must be 10AWG.

Or, convert the dryer to NEMA 6

You heard right. The trick is, they probably sell this dryer in the Philippines and other east Asian countries that have 240V power. And so they probably make a 240V-only version of this dryer. They designed the dryer from the ground up for this to be possible, and the difference is adding a small step-up/down transformer to power the internal 120V loads.

Don't want to plug/unplug? Sub-panel!

You need a real ground for this.

Remember that bit how those fat 30A connectors are not made for frequent plug/unplug? There's a way around this.

Install a sub-panel at the old dryer plug site. Use one with a main-breaker, any size over 30A will do since it's there to be a switch not a breaker. Don't scrimp on the breaker spaces. 20-30 is not too many. The neutral bus must be separate/isolated from the ground bus, because say it with me, neutral is not ground.

Then install a 30A breaker and bring it out to a 14-30 for the dryer.

Then install a 15A GFCI breaker and bring it out to a 6-15 for the jointer. The 5/6-15/20 receptacles are made for frequent unplug.

This setup has some sizing problems obviously - you can't run dryer and jointer at once for instance. Your local inspector may have an issue with that. But this is certainly the safest of available options. Also the most expense and work.

  • I'm feeling you think the NEMA 10-30 receptacle should be replaced? The NM 10/3 w/ ground that supplies said demon is connected (through a junction box and MC) to the main service panel. Since the dryer wants 2 hots and a white and the jointer wants two hots and a green, what if I replace the dryer receptacle with a NEMA 14-30 (2 hots, a white and a green), disconnect the grounding strap on the dryer, replace the pigtail on the dryer with a 4 wire 14-30 plug and replace the plug on my jointer extension cable with a 14-30 plug and not connect the white wire at the jointer end of that extension? – Tyler Dec 28 '16 at 13:23
  • NEMA 10 is deadly because a neutral failure in the cable electrifies the chassis of good equipment. I said convert to NEMA 6. On fitting a NEMA 14: yes IF you retrofit a ground wire back from the NEMA 14 to the panel it's served out of. You don't even need to go all the way if you can reach another junction box which has a 10AWG ground back to that same panel. You said earlier that there's no green wire in the supply cable going to the NEMA 10-30. Don't even think about attaching the white wire to BOTH neutral and ground on a NEMA 14. – Harper Dec 28 '16 at 16:34
  • I had no idea you still had an electric dryer and wanted to frequently swap connectors. Those fat 30A receptacles are not made for frequent use, and that stress on the receptacle will exacerbate exactly the failure that makes NEMA 10 kill people. In light of that, I revised above with an array of options. – Harper Dec 28 '16 at 17:29
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    Thanks, Harper for taking the time explain everything very clearly! You've answered all my questions including some I didn't know I should ask. I thought plugging the jointer into the dryer socket would save me work, but I see it isn't safe in the long term and won't save me work. I think that the best thing to do is to run a new 20 amp circuit from the panel with a 6-20R for the jointer and be done with it. Neutral is not ground! (I never thought it was which is why I started asking questions in the first place!) – Tyler Dec 28 '16 at 22:16
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Will it work? Yes.

Will an inspector not like it? Probably.

Since you were smart enough to understand how to create an adapter cord, I'm wondering why you just didn't go the distance and change the receptacle? The best thing to do is change the breaker to a 15 amp breaker, and change the receptacle to an NEMA 6-15 receptacle.

  • My plan is to alternate using the outlet for the jointer and dryer so replacing the receptacle with a NEMA 6-15 wont work. – Tyler Dec 28 '16 at 13:05

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