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Can I have something like this, or does the cable run from the panel to the subpanel need to be dedicated?

Main Panel+Breaker -> 40A dryer box with Outlet -> Subpanel+Breakers -> More circuits?

Note that I'm not plugging the subpanel into the outlet! Everything would be hard-wired, I just want to know if an outlet can exist on the same circuit that also feeds a subpanel.

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  • I don't know ALL the reasons this wont work, but your outlet would have to be protected by a 15-20A breaker rather than the presumably larger breaker for the subpanel. I'm sure there's more code reasons, but thats a practical deal breaker.
    – JPhi1618
    Sep 17 at 20:17
  • @JPhi1618, or it could be a 40A dryer outlet. Lets just assume that the subpanel's breaker is equal to the main panel's breaker that feeds the outlet.
    – KJ7LNW
    Sep 17 at 20:24
  • I think any outlet other than a standard 20A one needs to be on a dedicated circuit. You could run separate wires for the outlet, but run them together to make the job easier.
    – JPhi1618
    Sep 17 at 20:29
  • @JPhi1618, "any outlet other than a standard 20A one needs to be on a dedicated circuit" might answer the question if that is the rule. That would imply that subcircuits >20A must also be dedicated, I would think.
    – KJ7LNW
    Sep 17 at 20:31
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A feeder is breaker and wiring that supplies a subpanel.

A branch circuit is breaker and wiring that supplies various outlets, including receptacle outlets.

"Outlets" does include hardwired loads, or as they like to call them, "utilization equipment".

Wiring can be one or the other, not both. You cannot have outlets on a feeder.

So no.

The only exception I can think is if you have a reason allowed under 400.7 or 400.8 to have the subpanel be fed from an inlet or flexible cord plugged into an outlet. (yes, I know you said you don't mean that). For an example of pretty much this, look at a PDU as found on a computer rack. A PDU is basically a rack mount subpanel. However, your plan would require multiple receptacles - one for the subpanel and one for your load. The largest circuit which allows multiple receptacles is 30A. So that would limit usefulness of your subpanel.

The normal solution is to run a, say, 50A feeder to the subpanel, then have a 50A branch circuit fed off the subpanel. That is legit if the load calculation for the subpanel says that will work. Which it might if the other loads are just incidentals like lights and receptacles (e.g. circuits that allow 180 VA allotment per receptacle). You can't plan to overload a subpanel.

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  • Terminology wise, is a feeder strictly defined as that which feeds a subpanel, or is for feeding anything hard-wired (like a water heater)? (Also, who is Monica?)
    – KJ7LNW
    Sep 17 at 20:36
  • @KJ7LNW Monica info: meta.stackoverflow.com/q/393046/101039, lots to read, not sure if there is a good, short summary anywhere.
    – JPhi1618
    Sep 17 at 20:43
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    @KJ7LNW A feeder is breaker and wiring that supplies a subpanel. "Outlet" is a word that describes any connection to a load, including hardwired loads. A water heater is an outlet.
    – Harper - Reinstate Monica
    Sep 17 at 21:05
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First of all, a dryer receptacle is rated 30 amps, not 40, so if it's on a 40 amp breaker, you're already in violation.

If you truly have a 40 amp circuit (#8 copper wire minimum) the you're ok for the wires being on a 40 amp breaker but not the receptacle. If you have #10 copper on a 40 amp breaker then you are overfused.

Either way, there is nothing wrong with removing that receptacle and replacing it with a sub panel. If you're planning on still using the dryer and you have a 30 amp circuit and not 40 as you stated, then you probably don't have much headroom to additional loads imposed on that circuit as a dryer almost certainly will consume close to 80% of 30 amps. If you truly have a 40 amp circuit (#8 wire) then you could conceivably swap the receptacle for a small panel, then put the dryer receptacle on the new panel (this time on a 30 amp breaker and #10 wire) and add additional circuits to the panel. You wouldn't have much headroom though to add a whole lot. Maybe a few convenience receptacles and/or lighting circuits.

If you have #10 wire and it's in conduit, you could pull larger wire, say #8 or #6 to the new panel. I think you can get 3 #6 in 3/4 EMT with no ground wire (use pipe as ground).

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    Just ran the numbers on 3 #6 THHN in 3/4 EMT and you have plenty of space (137mm2 available, ~100mm2 used)
    – ThreePhaseEel
    Sep 19 at 1:19
  • So if you did that KJ, you could go 60 amps. That's enough for a small apartment! 😀
    – DrSparks
    Sep 19 at 1:24
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If wired the way you suggest the breaker would have to protect the outlet and the entire subpanel. The breaker and the outlet would have to match. There is no useful combination of breaker/outlet/subpanel that could work this way.

You can't run say a 60A subpanel off a 60A breaker and put a 20A outlet on the feeder cable.

If you use a 15A breaker and a 15A outlet, you don't need a subpanel, you could just run more 15A outlets along the same circuit. Same with 20A.

If you use, say, a 50A breaker the outlet must be 50A. Then, if it's allowed you could continue to a 50A subpanel. (I don't think that's allowed anyway). You could only attach a 50A device to the outlet and you could only use it if nothing was running off the subpanel. The whole arrangement would be pointless.

If you use an even bigger breaker the outlet would have to be correspondingly bigger and then there is literally no domestic device you could plug into it.

Instead

You could run the subpanel conduit through a box (it would have to be a larger than usual box) and install an ordinary outlet there but not connected to the feeder cables. Feed the outlet through wires coming back from the subpanel through the same conduit. Would that suit your needs? The need for the box to be larger, and to accommodate the larger conduit meant for the subpanel, might spoil your plans, depending on what they are.

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    I'm trying to understand if subpanel circuits must be home-runs not shared by anything else, or if it is acceptable (NEC) for multiple things like outlets, electric car chargers, etc to share the same circuit that feeds a subpanel.
    – KJ7LNW
    Sep 17 at 20:30
  • I don't think there is any practically useful arrangement that would be compliant. I think you could run a 20A circuit to some outlets and a subpanel with a 20A main, but obviously that would be pointless. Can you describe a specific arrangement that would not be obviously unsafe or obviously pointless? A 20A outlet on a 60A breaker, for example, is obviously unsafe AND obviously non-compliant. Can you be more precise?
    – jay613
    Sep 17 at 20:35
  • Subpanel off the box of the dryer's plug is the best example I can come up with, but @Harper points out that a feeder is not branch circuit which I think answers the question. However, it sounds like I could disconnect the dryer, insert a subpanel, and re-feed the dryer from the sub.
    – KJ7LNW
    Sep 17 at 20:39
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    Yes, exactly, if the objective is to avoid running more conduit, you can feed the outlet back from the sub. Just need to make sure the box is big enough to accommodate the feeder passing through.
    – jay613
    Sep 17 at 20:48
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    @KJ7LNW a single feeder can feed multiple subpanels, it just can't feed utilization loads directly in addition to feeding subpanels
    – ThreePhaseEel
    Sep 18 at 3:19

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