Residential Dryer circuit

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s.degidio

New member
Location
Minneapolis
I have a HOA requesting validation that a cloths dryer 30 amp outlet would have had to been wired with #10 conductor during 1985 construction of the building.

The issue is, I had #12 feeding a 30A dryer outlet on 30A breaker and aware of this violation had it rewired correctly.

I need a validation that in 1985 this circuit conductor had to be #10 and that #12 would under no circumstance be proper for this 30A circuit.
 

magoo5150

Member
Location
Mississippi
I thought code restricted it to 20amps?
The only thing restricted to 20A is the laundry branch circuit. This has nothing to do with the dryer outlet. I suppose if you wanted to put a industrial 100A dryer in, there would be no issue as long as the install was code compliant.
 

iwire

Moderator
Staff member
Location
Massachusetts
Out of curiosity, in what shape are those conductors in? :eek:

24 amps of load is no problem at all for 12 AWG.

I thought code restricted it to 20amps?

Yes for this application it is restricted.

Luckily copper can not read the NEC and handles more than allowed fine.:cool:


Not suggesting in the least I would wire a dryer outlet with 12 AWG just that I would not expect any conductor damage at all due to it.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Yes for this application it is restricted.

Luckily copper can not read the NEC and handles more than allowed fine.:cool:


Not suggesting in the least I would wire a dryer outlet with 12 AWG just that I would not expect any conductor damage at all due to it.

The copper might not melt, but wont the insulation break down over time? #12 is listed at 60*C at 20 amps.

EDIT: Ok you probably are right, looking at table 310 a second time 12 is listed for 30amps at 90*C, so in theory it might pull through I guess.
 
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al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
I have a HOA requesting validation that a cloths dryer 30 amp outlet would have had to been wired with #10 conductor during 1985 construction of the building.

The issue is, I had #12 feeding a 30A dryer outlet on 30A breaker and aware of this violation had it rewired correctly.

I need a validation that in 1985 this circuit conductor had to be #10 and that #12 would under no circumstance be proper for this 30A circuit.
OK. So you are fielding a question from a HOA (home owners association?).

If this clothes dryer is in the same jurisdiction that your signature is, 1985 would have been a transition year from the 1981 to the 1984 NEC. There was a local history of an "all-metal code" that had been relaxed around 1975.

To actually give a reasonable answer to your question, I need to know the wiring method for the clothes dryer branch circuit. Is it nonmetallic sheathed cable, an armored cable or inside a conduit or flex?

As a teaser: The ampacity table 310.16 in the 1981 NEC has the notation:
The load current rating and the overcurrent protection for conductor types marked with an obelisk shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; . . .
 

kwired

Electron manager
Location
NE Nebraska
The copper might not melt, but wont the insulation break down over time? #12 is listed at 60*C at 20 amps.

EDIT: Ok you probably are right, looking at table 310 a second time 12 is listed for 30amps at 90*C, so in theory it might pull through I guess.
NM Cable at that time may not have been "NM-B". I don't know when it was introduced but if not then it wasn't too much later.

Bottom line is NEC restrictions are below what the actual insulation can take to build in a certain safety factor. That plus if this conductor were continuously loaded 24/7 vs the occasional 20-45 minutes it likely sees, or if it were bundled with a bunch of other conductors that also contribute heat the the bundle you may see a difference in degradation - but that is also part of why NEC does require ampacity adjustments for some situations.

Also take notice that values in table 310.15(16) are for ambient of 30C (86F) so operation at lower temp actually would mean it can take more current, but 240.4(D) still trumps this when it comes to a minimum size.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Only some circuits require restricting 12 AWG to 20 amps.

Items like motors and welders can ignore 240.4(D)


Ive never understood that. I could understand welders because they are intermittent (duty cycle), but why are motors allowed to load conductors to the max?
 
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