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I have a garage subpanel with 6 spaces. They are currently consumed by the following circuits:

  • One for lighting.
  • One for a few 120V outlets.
  • Two for a 20A 240V circuit for a well pump.
  • Two for a 20A 240V circuit for a saw.

Now I just acquired a 4800W shop heater with a 6-30P plug, so apparently I now need a 30A 240V circuit.

Am I practically able to avoid running another circuit? The options I can imagine off the top of my head are:

  • Wire up a new single circuit outlet for the heater. However, I'd like to avoid installing a new panel if at all practically possible.
  • Tear out the 20A circuit I ran (not a big deal) and run a new 30A circuit. Install an identical plug on my saw so that I can use the outlet for either the saw or the heater.
  • Get ride of the heater and buy something that works with what I've currently got. However, it appears to me that all heaters of this type use the same plug, so I'm not sure if this is possible.
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    You're asking "is something wrong with the design" — but what is the design? How many spaces does your current subpanel have, and what are the circuits currently used for? Please edit your question to give more details, and people will then be able to give more detailed recommendations in the answers. – Kevin Reid Dec 14 '20 at 20:23
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    This appears to be a 4000W version of the style of heater you linked, and it comes with a NEMA 6-20 plug, which should be compatible with your saw circuit. amazon.com/Dimplex-DGWH4031-Shop-Heater-Almond/dp/B00064NURU – Nate S. Dec 14 '20 at 21:16
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    It would be a code violation to connect your 20 amp rates saw to a 30 amp circuit. – Ed Beal Dec 14 '20 at 21:25
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    ^ not just a code violation, but a Bad Idea™. – FreeMan Dec 14 '20 at 23:43
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    You don't have too many things, you have too few panel spaces. Given that it's only 4 circuits, shut the supply breaker off, tear the 6-space panel off the wall, and replace with a 30-space. Our slogan around here is "go BIG or go home" on panel spaces, we're not out to waste your money, we're out to make sure THIS never happens because it's a PITA and it's unnecessary. – Harper - Reinstate Monica Dec 15 '20 at 2:23
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There is one way you could do this without a panel replacement that would be safe - whether or not it would be "to code" I'll leave up to the peanut gallery. (who I am sure will not like this answer at all)

Tear out your 20A circuit and replace it with a 30A with a 30A receptacle. Not only replace the plug on the saw - but replace the entire CORD on the saw with a 30A cord and terminate the cord in a "motor controller switch" mounted on the saw that has properly rated overload heaters in it that are sized for the current draw of the motor at 240v (which is likely to be around 6-7 amps if it's a table saw like I'm thinking) Then run the regular cord from the motor controller/switch to the motor.

Building codes don't cover internal appliance wiring and of course the moment you modify the saw (by replacing the cord) you are no longer covered by UL or any of the other certifications and you are letting the manufacturer off the hook should the saw burn the place to the ground. But, it is "safe" (as safe as any saw can be - which isn't much) since the motor controller switch protection is no worse than a breaker (and probably better) And considering the number of tool manufacturers who have bit the dust over the last 2 decades there's a good chance your saws manufacturer isn't around to sue anyway even if you didn't modify it and it burned the place to the ground.

I have a shop full of older metal woodworking tools made in an era where the prevailing wisdom was something along the lines of "we don't need no steenking ground wires" and were all, in their day "to code" so I tend to take "code" with a bit of suspicion.

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    As a licensed electrician from the peanut gallery you have described yet another code violation, since you are unaware of the code do not make statements that you have no clue about! NEC article 400 is all about flexible cords! There are rules for appliances and cord connected devices, motor driven devices do have different rules but those only apply to startup. Advising someone to do something in direct violation of code is not what we are about. – Ed Beal Dec 15 '20 at 15:06
  • Just because 50 year old tools were built to the best knowledge available 50 years ago doesn't mean new things haven't been learned since that makes a more modern tool safer. Taking "code" with a bit of suspicion means you don't value your life all that much. Don't advise others to devalue their lives because of your poor judgement. – FreeMan Dec 15 '20 at 19:59
  • The NEC article does not cover building codes you don't use flexible cords as permanent building wiring. I did not say that there is no NEC code for appliance wiring, you are the one who claimed I said that. I said NEC building wiring codes don't specify appliance wiring. Telling him what kind of cord to use per 400 is pointless. It will be safe as long as he maintains 30A capacity to a protective device on the saw and as I said I wasn't going to address the "codeliness" because the second he touches the cord he's on his own. – Ted Mittelstaedt Dec 16 '20 at 12:04
  • FreeMan, code still allows opportunities to be unsafe. Such as multiple outlets on a single circuit. The NEC is faced with the fact that nobody is going to buy a panel with 300 slots and home run every outlet in a residential house to it's own breaker so they allow that. Nothing prevents a homeowner from plugging 2-3 1500watt space heaters into the same circuit and if the breaker is bad burning the place down. Unless you fully understand the intent of code you can create unsafe wiring. I trust 50 year old code much less than todays code but only fools blindly trust code without question. – Ted Mittelstaedt Dec 16 '20 at 12:17

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