Reduced neutral to dryer

[FionaZuppa]

My understanding is the NEC lets you do load calcs without the nameplate known, but I am still unsure how the neutral factors into that.

so how would you apply this, kinda says you need to know the max load to be served, yes? which isn't really an issue if you size (minimum ampacity) all the CCC's to the max amp rating of the receptacle. if its a 30A recept then wire it with #10 for all CCC's.

(b) The minimum branch-circuit conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.

oddly, the 80% rule (125% from the other way) means a 30A OCPD is no good for a GE electric dryer that is plated 25A, yet the install instructions say to use 30A ckt.


but let me ask a more fundamental Q. why pull a #12 CCC ? is the conduit fill an issue? if it were a $$ thing because the project was 20k feet of white wire, then pull #10 white and #12 green <-- which works out to the same $$ btw (20k feet of #10green + 20k feet of #12white = 20k feet of #10white + 20k feet of #12green).

we know these common appliances dont use that much amps on the 120 side, but that doesnt mean an appliance (device, whatever) cant use say 21A on the 120 side.

 

[growler]

Ie, its not uncommon to find a NEMA 14-50 range outlet fed by a 40amp circuit.

Can you have a 30 amp dryer receptacles fed by a 20 amp circuit ? They make a 20 amp 240V receptacle.

I would think that a reduced neutral would not be allowed because the overcurrent protection of the circuit would be at 30 amps and therefore the conductor would have to be #10. The neutral may not normally carry 30 amps but during a fault (motor locking) it may be exposed to a higher current and need to be protected.

 

[jumper]

Can you have a 30 amp dryer receptacles fed by a 20 amp circuit ? They make a 20 amp 240V receptacle.

A receptacle-yes. 210.21(B)(1)

Receptacles-no. 210.21(B)(3)

I would think that a reduced neutral would not be allowed because the overcurrent protection of the circuit would be at 30 amps and therefore the conductor would have to be #10. The neutral may not normally carry 30 amps but during a fault (motor locking) it may be exposed to a higher current and need to be protected.

This idea is somewhat reinforced by 240.4(D) for small conductors. #10 and less.

 

[mbrooke]

so how would you apply this, kinda says you need to know the max load to be served, yes? which isn't really an issue if you size (minimum ampacity) all the CCC's to the max amp rating of the receptacle. if its a 30A recept then wire it with #10 for all CCC's.

There is simply no way of knowing the amount of neutral current any one dryer will contribute just going by the nameplate. And even if you could, whats to say the next dryer in 15 years will be the same?

oddly, the 80% rule (125% from the other way) means a 30A OCPD is no good for a GE electric dryer that is plated 25A, yet the install instructions say to use 30A ckt.


but let me ask a more fundamental Q. why pull a #12 CCC ? is the conduit fill an issue? if it were a $$ thing because the project was 20k feet of white wire, then pull #10 white and #12 green <-- which works out to the same $$ btw (20k feet of #10green + 20k feet of #12white = 20k feet of #10white + 20k feet of #12green).

we know these common appliances dont use that much amps on the 120 side, but that doesnt mean an appliance (device, whatever) cant use say 21A on the 120 side.

In my experience a clothes dryer's heating element(s) does not run for 3 hours straight. My Whirlpool built dryer runs for about the first 15-20 minutes without the heating element shutting off on a full load; as the moisture content drops the exhaust temperature goes up the heater starts to cycle on and off. As the cycle nears to an end the element off time becomes greater and the element on time becomes smaller. My previous GE dryer had 2 heating elements. Both would come on when started and one would drop out about 5-10 minutes latter when the dryer fully warmed up with the other cycling on and off as needed to maintain selected temps.


The OP mentioned using 12 because he ran out of #10.

 

[mbrooke]

Can you have a 30 amp dryer receptacles fed by a 20 amp circuit ? They make a 20 amp 240V receptacle.

I would think that a reduced neutral would not be allowed because the overcurrent protection of the circuit would be at 30 amps and therefore the conductor would have to be #10. The neutral may not normally carry 30 amps but during a fault (motor locking) it may be exposed to a higher current and need to be protected.

Id argue the motor's thermal cutoff would open before the wire was subjected to a continuous current exceeding 20amps. My real life worry would be someone dragging home a kiln that put 24 amps on the neutral.

A receptacle-yes. 210.21(B)(1)

Receptacles-no. 210.21(B)(3)



This idea is somewhat reinforced by 240.4(D) for small conductors. #10 and less.

Yup- single receptacle. In theory a single 5-20r could be placed on a 15 amp circuit... Seen it done where 120 volt power vent gas water heaters were installed in the basement tapping of the lighting circuit.

 

[FionaZuppa]

Ie, its not uncommon to find a NEMA 14-50 range outlet fed by a 40amp circuit.

i lookup a GE range, says its rated 40A, it lists all of the elements totaling 9150watts, which on 240v thats 38.125A, 125% sizing says i should have a 47.6A wire. install instructions say to use a 40A ckt. NEMA 14's are 30 & 50, so you cant use the 30A version, yet the install instructions says:

A 50 amp range cord is not recommended

odd, so if the range rating is above a 14-30 then i need to use a 14-50 recept, so why would a 50A cord not be good?

if i install a NEMA 14-50 then i would wire for 50A (#8 wire for CCC's) and then use 40A OCPD to match the appliance specs.

 

[mbrooke]

i lookup a GE range, says its rated 40A, it lists all of the elements totaling 9150watts, which on 240v thats 38.125A, 125% sizing says i should have a 47.6A wire. install instructions say to use a 40A ckt. NEMA 14's are 30 & 50, so you cant use the 30A version, yet the install instructions says:

odd, so if the range rating is above a 14-30 then i need to use a 14-50 recept, so why would a 50A cord not be good?

if i install a NEMA 14-50 then i would wire for 50A and then use 40A OCPD to match the appliance specs.

Look at it like this:

1. A range is not a continuous load

2. Not all burners and elements will be on at once- on high.

You can use a 50amp cord, nothing will harm the circuit, range or safety of the occupants. "not recommended" is there way of saying 'not mandatory' FWIW, never take the instructions word for word, you will find a lack of technical proof reading.

 

[FionaZuppa]

Look at it like this:

1. A range is not a continuous load

2. Not all burners and elements will be on at once- on high.

You can use a 50amp cord, nothing will harm the circuit, range or safety of the occupants. "not recommended" is there way of saying 'not mandatory' FWIW, never take the instructions word for word, you will find a lack of technical proof reading.

thanks for catching my-bad there (my bad --> my post #46 & #41 was not correct, sorry...... i did mean to highlight that at 100% non-cont you still need #8 wire and 14-50 recept for the ~38A range, or #10 14-30 for a 25A dryer)
a range has potential to run full amps in non-cont mode, yes?
so you size the wire how? #10 is still not enough to cover rated amps, #8 covers it, which means the use of a 14-50 recept. a 40A ocpd is fine, but at least the recept has wire to match, etc. as for the 50A cord not recommended, instructions say something about the cord being marked for use in 13/8 inch opening, i guess the punchout in back of range is limited in size, so maybe a safety issue there by using the larger cord?

 

[mbrooke]

100% cont + 125% non-cont, yes ??
a range has potential to run full amps in non-cont mode, yes?
so you size the wire how? #10 is still not enough to cover rated amps, #8 covers it, which means the use of a 14-50 recept. a 40A ocpd is fine, but at least the recept has wire to match, etc. as for the 50A cord not recommended, instructions say something about the cord being marked for use in 13/8 inch opening, i guess the punchout in back of range is limited in size, so maybe a safety issue there by using the larger cord?

There is no continuous. Full amps if one deliberately set all the burners on high and the broiler on high- such has no practical application in the real world for cooking and does not happen- other than a 1 minute test during a home inspection verifying your new investment has a working stove.

The manufactures know that and so do the CMPs. They let stoves go by a different set of rules. In fact you can do this:

(3) Household Ranges and Cooking Appliances. Branchcircuit
conductors supplying household ranges, wall-mounted
ovens, counter-mounted cooking units, and other household
cooking appliances shall have an ampacity not less than the
rating of the branch circuit and not less than the maximum
load to be served. For ranges of 83⁄4 kW or more rating, the
minimum branch-circuit rating shall be 40 amperes.

Exception No. 1: Conductors tapped from a 50-ampere
branch circuit supplying electric ranges, wall-mounted
electric ovens, and counter-mounted electric cooking units
shall have an ampacity of not less than 20 amperes and
shall be suffıcient for the load to be served. These tap conductors
include any conductors that are a part of the leads
supplied with the appliance that are smaller than the
branch-circuit conductors. The taps shall not be longer
than necessary for servicing the appliance.

Exception No. 2: The neutral conductor of a 3-wire
branch circuit supplying a household electric range, a
wall-mounted oven, or a counter-mounted cooking unit
shall be permitted to be smaller than the ungrounded conductors
where the maximum demand of a range of 83⁄4-kW
or more rating has been calculated according to Column C
of Table 220.55, but such conductor shall have an ampacity
of not less than 70 percent of the branch-circuit rating and
shall not be smaller than 10 AWG.

 

[FionaZuppa]

There is no continuous.

understood, i made my noted corrections.
but non-cont doesnt mean "not full rated load", which is reflected in the install instructions, so you end up with #8 to the range, or #8 to a 14-50 (#10 or #10 to a 14-30 for ~25A dryer).

post #29, ok, for a range. for the dryer Q, that rule does not apply. all CCC's to a dryer should be of same ampacity.
why are 2-pole (3 CCC) dryers excluded ??

 

[mbrooke]

understood, i made my noted corrections.
but non-cont doesnt mean "not full rated load", which is reflected in the install instructions, so you end up with #8 to the range, or #8 to a 14-50 (#10 or #10 to a 14-30 for ~25A dryer).

post #29, ok, for a range. for the dryer Q, that rule does not apply. all CCC's to a dryer should be of same ampacity.

Its ok

In all honesty you could end up with a range that pulls 45 amps with everything on full blast connected to a 40amp circuit while still being code; but still, its not something that will ever take place for any significant amount of time- if ever.

 

[FionaZuppa]

Its ok

In all honesty you could end up with a range that pulls 45 amps with everything on full blast connected to a 40amp circuit while still being code; but still, its not something that will ever take place for any significant amount of time- if ever.

Exception No. 2: The neutral conductor of a 3-wire
branch circuit supplying a household electric range, a
wall-mounted oven, or a counter-mounted cooking unit
shall be permitted to be smaller than the ungrounded conductors
where the maximum demand of a range of 83⁄4-kW
or more rating has been calculated according to Column C
of Table 220.55, but such conductor shall have an ampacity
of not less than 70 percent of the branch-circuit rating and
shall not be smaller than 10 AWG.

whats to say a fault in range does not put ~36A of amps onto the neutral? i have 50A ocpd with #8 THHN but a #10 neutral. i guess the NEC just sees this as low probability of occurrence, yet just one occurrence could mean possible injury or worse?

 

[mbrooke]

whats to say a fault in range does not put ~36A of amps onto the neutral? i have 50A ocpd with #8 THHN but a #10 neutral.

The bulk of the loads are L-L connected. The largest element shorting to ground (near one end) will not put that much current on the neutral, and if it did it would not hold up very long. Anything else would be a direct short circuit which would trip the OCPD very fast.

 

[FionaZuppa]

The bulk of the loads are L-L connected. The largest element shorting to ground (near one end) will not put that much current on the neutral, and if it did it would not hold up very long. Anything else would be a direct short circuit which would trip the OCPD very fast.

this thought though is way different than a dryer? not that it would matter even if the downgrade exception applied to dryers as it says #10 min.

 

[Smart $]

Well, IMHO no since its saying other than receptacle outlets. A receptacle is an outlet, but not all outlets are receptacles. Here is the definition of outlet:

I could be very wrong though.

your view of outlet is correct. but perhaps "receptacles" are excluded by that 18" verbiage?

That's the question. Where it says "other than receptacle outlets," does that mean no receptacle outlets permitted on taps or individual receptacle outlets are permitted with taps over 18"? :angel:

 

[FionaZuppa]

That's the question. Where it says "other than receptacle outlets," does that mean no receptacle outlets permitted on taps or individual receptacle outlets are permitted with taps over 18"? :angel:

considering the verbiage and context, i think NEC intends to mean that receptacles "not permitted". it reads/written very legal like, the verbiage applies to, as stated, except to receptacles.

mark that section as an area needing new verbiage for clarity.

 

[kwired]

215.2(A)(2) says the grounded conductor of a feeder circuit can't be any smaller then the required equipment grounding conductor.

For minimum size of grounded service conductot 230.42.(C) sends you to 250.24(C) which sends you to Table 250.102(C)(1).

There is no similar section stating minimum grounded conductor size for branch circuits.

In all cases the conductor must be sized at least for the load it is intended to carry, so even if in the feeder situation the minimum EGC size were 10 AWG, if you had a calculated neutral load of 40 amps you still would need at least 8 AWG.

Personally I wouldn't have much concern even if the dryer had a 14 AWG neutral ran to it. I bet it never sees more then 5-6 amps, worst case efficiency maybe up to 10 amps.

 

[Smart $]

considering the verbiage and context, i think NEC intends to mean that receptacles "not permitted". it reads/written very legal like, the verbiage applies to, as stated, except to receptacles.

mark that section as an area needing new verbiage for clarity.

I agree it is intended to exclude a receptacle outlet being powered by a circuit conductor tap. But we should not have to assume CMP intentions, so also agree the verbiage needs clarification.

 

[FionaZuppa]

In all cases the conductor must be sized at least for the load it is intended to carry, so even if in the feeder situation the minimum EGC size were 10 AWG, if you had a calculated neutral load of 40 amps you still would need at least 8 AWG.

a 2-pole 3 CCC dryer, you calculate neutral amps how exactly? for that matter, a 2-pole 3 CCC NEMA 14-, the neutral calc is what ??
this is why i am saying just match the wire to the recept accordingly. 14-50 needs #6 NM, or #8 THHN in conduit. i dont see where NEC stops #8 NM to a 14-50 as long as OCPD is no more than 40A, there is no 14-40 to use, etc. but i see where folks may see a 14-50 and think the ckt is good for 50 if they swap out the 40 to a 50 ocpd.

this falls into same argument of running #14 to 20A rated recepts using 15A ocpd. seems plausible, very possible that someone uses a real 20A device and keeps tripping breaker, but then they decided to swap the breaker to a 20A = bad.

with a dryer on a 14-30, #10 will be min wire size, so if the ocpd was for some reason a 25a ocpd and i swapped that to a 30a, no issue.

 

[JFletcher]

I'm sure the nameplate of the dryer, instructions, or the terminal block will specify minimum #10 copper conductors, so a #12 neutral will be a 110.3(B) violation.