Dryer Outlet

[iwire]

isnt that a max load table?

No, Table 210.21(B)(3) is not Table 210.21(B)(2).

Different tables, different goals.

Table 210.21(B)(3) prohibits supplying a 50 amp receptacle from a 30 amp circuit.

Furthermore we cannot decide to use a 50 amp circuit to supply a typical residential dryer. Sections in article 422 will prohibit us from supplying the 24 amp dryer with a 50 amp circuit.

 

[FionaZuppa]

No, Table 210.21(B)(3) is not Table 210.21(B)(2).

Different tables, different goals.

Table 210.21(B)(3) prohibits supplying a 50 amp receptacle from a 30 amp circuit.

Furthermore we cannot decide to use a 50 amp circuit to supply a typical residential dryer. Sections in article 422 will prohibit us from supplying the 24 amp dryer with a 50 amp circuit.

how does 210.21(B)(3) apply ??
two or more receptacles
cord/plug arc welder
electric discharge lighting

isnt dryer outlet a single, and the only one on the bc?

and rather baffling, a 2+ outlet (thats one dual receptacle device btw) bc can have 15A rated devices on 20A ocpd, yet we cant use all 20A rated outlets when ocpd is 15A? that seems like wrong logic to me.

15A rated outlets should be discontinued, since NEC says the ocpd defines the bc rating. all std residential outlets should be the 20A type, whether it can support 20A or not doesnt matter, the ocpd defines the bc rating. 20A outlets that have 20A ocpd might perhaps have a "dot" on them?

(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.


Exception No. 1: Receptacles for one or more cord-andplug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity permitted by 630.11(A) or (B) as applicable for arc welders.


Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to bebased on 410.62(C).

Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits

 

[iwire]

how does 210.21(B)(3) apply ??
two or more receptacles
cord/plug arc welder
electric discharge lighting

isnt dryer outlet a single, and the only one on the bc?

You are correct, I forgot that table only applies to multiple receptacles.

Still a bad design to place a 50 amp outlet at the location for a 30 amp dryer.

15A rated outlets should be discontinued,

Why?

 

[FionaZuppa]

You are correct, I forgot that table only applies to multiple receptacles.

Still a bad design to place a 50 amp outlet at the location for a 30 amp dryer.

Why?

well, dryer just says "30A min". if the outlet device can handle 1000A and the wiring is good for 40A and ocpd is 30A, why is that a issue?

why rid 15A rated?
because having one type of "std" outlet that handles both 15 and 20A ocpd's, just seems easier. we cant police if a 15A ocpd gets replaced by a 20A ocpd w/o regard to the wiring.

would it not just be safer for NEC to say that all residential wiring be #12min, and then dictate in what areas/location should be restricted to 15A ocpd? this way you get safety from the bigger wire while at the same time you control how much energy can get there.

 

[iwire]

well, dryer just says "30A min".

What?

because having one type of "std" outlet that handles both 15 and 20A ocpd's, just seems easier.

We have those, they are caledl 20 amp receptacles and you are free to install them on as many 15 amp circuits as you would like.

However the manufacturers charge more for 20s so 15s are used where allowed.

we cant police if a 15A ocpd gets replaced by a 20A ocpd w/o regard to the wiring.

Ahh, with that argument we might as well shut the grid down as we can never prevent that sort of thing.

would it not just be safer for NEC to say that all residential wiring be #12min, and then dictate in what areas/location should be restricted to 15A ocpd? this way you get safety from the bigger wire while at the same time you control how much energy can get there.

Sure, if money was not a consideration.

 

[FionaZuppa]

hah, i think i am on same boat as you iwire, you the captain and me just the engineer..... a little different speak if you will.

open a dryer install doc, "30A min" is what most say for the supply.

so for OP, just spec a 14-30R with proper wire size and a 30A ocpd. done.

 

[Jraef]

NEMA nomenclature is not random, it is very specific. 14-30R is NOT for 3 phase. The "14" specifically means SINGLE phase, 125/250V 3 pole 4 wire, i.e. as used for a dryer (unless the dryer is rated for 40 or 50A of course). 3 phase would be a 15, not a 14.


Part of the confusion is the word "pole" (I know from experience). "Pole" in NEMA world means "current carrying conductor", and the Neutral is considered a current carrying conductor. So 3 "pole" 4 wire could be applied to a single phase circuit that needs to use the two power lines plus the neutral, but could also apply to a 3 phase Wye, or 3 phase DELTA GROUNDED CENTER TAP circuit device. Hence NEMA's use of the specific nomenclature to (attempt to) prevent that from happening. In the 30A devices (which are more common), they also make the Neutral pin an L shape.

In the NEMA 15-30 it is straight.


Where it gets more confusing is when you get to 50 and 60A devices. They all look the same to the naked eye at first glance, but the spacings and blade orientations are different if you can compare them side by side.