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I need to plug in my compressor, which has a NEMA L6-30P plug.

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I currently have a NEMA 10-30R Receptacle enter image description here

How do I do this? It looks like the ground from my dryer plug is grounded in the box. I do have a rod that runs into the ground outside my house. Can I run a separate plug off my dryer plug and attach it right next to the dryer plug for my compressor? They both won't be running at the same time.

Edited in from comments on an answer:

  • The dryer plug is in a metal box that runs through a foot of metal conduit up to the electrical box that runs to a 30 amp breaker.

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  • Despite the edit (well done), it's still a bit difficult to decipher what you're trying to do. At a minimum we need the electrical requirement info on the compressor. Are you flat out of outlets in the house, so you want to share the outlet with the dryer? Do you want to extend the dryer's circuit to add an additional outlet? Feel free to edit to clarify.
    – FreeMan
    Commented Dec 8, 2020 at 16:30
  • Does your dryer plug have a metal box which is connected to a metal electrical cable or conduit? If so, the ground may be fine. You could carefully test it using a VOM or a three-light tester and probes. Commented Dec 8, 2020 at 16:33
  • google.com/search?q=NEMA+L6-30P+to+10-30r
    – isherwood
    Commented Dec 8, 2020 at 17:17
  • Can you post photos of the inside of your dryer receptacle box please? Commented Dec 9, 2020 at 1:00
  • Pics imgur.com/a/rTJu4Zw
    – Mike Dirks
    Commented Dec 11, 2020 at 1:55

3 Answers 3

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Given the proximity of the 10-30R receptacle to the panel, and the presence of conduit connecting the two, you could upgrade the 10-30R to a 14-30R and likewise swap out the power cord on the dryer. That's something like US$25 in parts. This is an upgrade that is just good sense to implement.

If you upgrade to a 14-30R then you could easily make or buy an adapter from the 14-30P to L6-30R. It would deal with the ground-vs-neutral situation correctly.

There's also another option. Since the panel is just right there, get a bit of conduit and a box and install a new L6-30R receptacle. I believe code allows multiple 30A receptacles to be fed from a 30A breaker. If the panel has no room for a new breaker and you don't want to replace existing breakers with a quad breaker solution, you could choose to feed both receptacles from the one existing breaker. The terminal on your breaker might be designed for landing two conductors, but if not, attach a pigtail of wire to the breaker and use a wire nut to join the pigtail with the leads going to the two receptacles (times two: this same arrangement for both poles of the breaker).

The two-receptacles-one-breaker arrangement could be accomplished by putting the junction in the box with the dryer outlet but it might violate box fill rules and definitely would be crowded and hard to work with. It'll be much easier to run the conductors from a new receptacle directly into the breaker box and make the junction there.

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  • 2
    Absolutely! That NEMA 10 connection is a child-killer. For any dryer connected NEMA 10, a single point of failure (loose neutral connection) WILL energize the chassis of the dryer. What are the chances of someone touching that and a grounded thing? The washing machine chassis is grounded. Commented Dec 8, 2020 at 20:24
  • And part of changing the cord on the dryer must be removing the neutral-to-ground bonding strap. Tie it down somewhere safe that isn't the neutral pole :) Commented Dec 8, 2020 at 20:31
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No you can't legally tap wire for wire from the receptacle, the NEMA 6 is two hots and a ground, NEMA 10 is two hots and a neutral that by special exception allows grounding via the neutral conductor (NEC 250.140 exception). If you just even had the compressor plugged in you would be exposing dryer current to the compressor ground.

You could run a ground wire from the panel through the dryer outlet box, but then you no longer satisfy the NEMA 10 exception which specifies "where an equipment grounding conductor is not present", so you would have to replace your dryer receptacle and cord with a safer NEMA 14.

From your description in the comments to other answer I don't think your NEMA 10 is legal at all. The exception allows the metal box to be connected to the neutral, but the section doesn't specify grounding metal raceway, ostensibly since then an equipment ground is present. I realize existing installations are subject to the code at the time of install, but I doubt the 10 was ever legal with grounding raceway.

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  • 1
    It was never illegal to use EMT conduit. And there was a point in time when it was legal to install a NEMA 10 recep in any installation including EMT conduit. However, the NEMA 10 neutral was still neutral and required an insulated white wire. You could not use EMT shell as a neutral substitute. OP should convert the recep and dryer to NEMA 14, and then will be free to use a NEMA 6-NEMA 14 adapter cable; that particular cable is legal. Commented Dec 8, 2020 at 20:30
  • Ok guys sorry been little busy this is what I have going on
    – Mike Dirks
    Commented Dec 11, 2020 at 1:56
  • imgur.com/gallery/fXu6Io2
    – Mike Dirks
    Commented Dec 11, 2020 at 2:02
  • There are some pics of what I have going on. And that strip all the grounds run to isn't that the ground strip on neutral. And the box is grounded to a rod that runs outside and into the ground
    – Mike Dirks
    Commented Dec 11, 2020 at 2:03
  • You got big problems here, bonded neutral is only legal at service, and you have way more than 6 main disconnects allowed in a service panel. And you have breakers not NRTL approved for the panel. Commented Dec 11, 2020 at 2:14
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Simple answer is yes if they are both 240v.

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  • Ok so the dryer plug is in a metal little box that runs through a foot of metal tube up to the electrical box that runs to a 30 amp breaker. The ground is ran to a strip in the breaker box that is in line with all the other grounds. I dont have anymore breakers to run a extra breaker for my compressor.
    – Mike Dirks
    Commented Dec 8, 2020 at 16:53
  • Compressor says 230volt. The plug on compressor says 30a-250v 3prong nema L6-30. Dryer plug is the 3 prong 10-30r
    – Mike Dirks
    Commented Dec 8, 2020 at 17:00
  • 1
    Don't hold discussions via backchannels. Post your images here. You were advised to upload to imgur.com and link here.
    – isherwood
    Commented Dec 8, 2020 at 17:15
  • A TL;DR section is good, however, a little more meat is considered very helpful.
    – FreeMan
    Commented Dec 8, 2020 at 17:45
  • Pics imgur.com/a/rTJu4Zw
    – Mike Dirks
    Commented Dec 11, 2020 at 1:56

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