Downsized neutral for dryer circuit

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SceneryDriver

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Code to use #12 for the neutral on a 30A, 4-wire dryer circuit run in conduit? A colleague asked me, and I wasn't actually sure. So many are wired with 10/3 Romex, and so few with conduit that I never gave it a thought. Practically, it's got to be fine - dryers only use the neutral for the motor, but is it code compliant?

I searched for and found a thread on this here, but it just devolved into arguing (who... us?!) with no clear answer.


Thanks,

SceneryDriver
 
210.19 states branch circuit conductors shall have an ampacity based on the load served. In the case of most dyers the neutral load would allow a smaller conductor than the phase conductor.
 
Remember that the neutral must have an ampacity sufficient for the load served and can be no smaller then the required EGC.

A #14 would be sufficient for the neutral load on a dryer, but the EGC on a 30A circuit is a #10, so the smallest allowed neutral is a #10.

Perhaps something that should be revisited given GFCI protection.

Jon
 
winnie said:
Remember that the neutral must have an ampacity sufficient for the load served and can be no smaller then the required EGC.

A #14 would be sufficient for the neutral load on a dryer, but the EGC on a 30A circuit is a #10, so the smallest allowed neutral is a #10.

Perhaps something that should be revisited given GFCI protection.

Jon
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That has been my thinking based primarily on 215.(2)(B) but I fail to find the same wording for branch circuits. Do you have a Code reference ?
 
augie47 said:
That has been my thinking based primarily on 215.(2)(B) but I fail to find the same wording for branch circuits. Do you have a Code reference ?
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At one point I believe I sent a public input for this exact reason-- there is nothing directly stating the same for branch circuits as it does for feeders. I cannot remember- I may have actual forgot to send it in but I remember reading comments about it. They didn't feel it necessary.

I see it basically as Larry put it. The neutral needs to be sized for the circuit as stated in 240.4 and then 240.4(D) states the ampacity of those conductors

240.4 Protection of Conductors. Conductors, other than flexible
cords, flexible cables, and fixture wires, shall be protected
against overcurrent in accordance with their ampacities specified
in 310.15, unless otherwise permitted or required in
240.4(A) through (G).
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Sizing neutrals - a tale. I was asked to look at a problem neutral in a large hotel. It was running hot. and getting hotter as more units were commissioning. The phases and neutrals were the same sizes and that was the usual practice. The problem was harmonics. Up rating all the neutrals would have been a major tasks - all the cabling was already installed. What I did was installed harmonic filters. I have done that for VFDs in industrial applications. This was the first for me for a hotel.
 
Besoeker3 said:
Sizing neutrals - a tale. I was asked to look at a problem neutral in a large hotel. It was running hot. and getting hotter as more units were commissioning. The phases and neutrals were the same sizes and that was the usual practice. The problem was harmonics. Up rating all the neutrals would have been a major tasks - all the cabling was already installed. What I did was installed harmonic filters. I have done that for VFDs in industrial applications. This was the first for me for a hotel.
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Interesting and amazing that harmonics can really get that "bad" to cause the neutral to overheat. But how is that related to the original poster's question on branch circuits? lol I don't want the thread to make a turn in a different direction.
 
Dennis Alwon said:
Interesting and amazing that harmonics can really get that "bad" to cause the neutral to overheat. But how is that related to the original poster's question on branch circuits? lol I don't want the thread to make a turn in a different direction.
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Just that SceneryDriver and others may know that harmonics can be a problem that may require consideration for the neutral ratings.
 
Dennis Alwon said:
At one point I believe I sent a public input for this exact reason-- there is nothing directly stating the same for branch circuits as it does for feeders. I cannot remember- I may have actual forgot to send it in but I remember reading comments about it. They didn't feel it necessary.

I see it basically as Larry put it. The neutral needs to be sized for the circuit as stated in 240.4 and then 240.4(D) states the ampacity of those conductors
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240.21 however says the overcurrent protection goes in each ungrounded conductor.

As mentioned earlier 215.2 has minimum size requirement for neutral conductors in feeders, but there is no similar language in art 210 for branch circuits.

If you had a branch circuit to a single 208 or 240 motor load that had 120 volt controller and had 50 amp plus ungrounded conductors, there is nothing wrong with running a 14 AWG neutral for those controls, presuming only neutral load is contactor coil or control relays and timers or such in the branch circuit portion of the supply. If there is a feeder portion, technically that must comply with 215.2 and would need to be same size as minimum required EGC.
 
So Article 220 Part III "Feeder and Service Load Calculations" has section 220.61 on "Feeder or Service Neutral Load." Whereas Article 220 Part II "Branch-Circuit Load Calculations" has nothing comparable.

Therefore the branch circuit neutral load is always considered to be equal to the ungrounded conductor load, and is protected from overload by the OCPD, just like the ungrounded conductors. While a feeder or service neutral may be smaller than the ungrounded conductors, and is protected from overload only by the section 220.61 computation.

Correct?

Cheers, Wayne
 
kwired said:
If you had a branch circuit to a single 208 or 240 motor load that had 120 volt controller and had 50 amp plus ungrounded conductors, there is nothing wrong with running a 14 AWG neutral for those controls, presuming only neutral load is contactor coil or control relays and timers or such in the branch circuit portion of the supply.
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The control wiring may be allowed to be smaller, but the branch circuit's grounded conductor must be able to be protected from overload by the same OCPD as that which protects the 50-amp conductors.
 
wwhitney said:
So Article 220 Part III "Feeder and Service Load Calculations" has section 220.61 on "Feeder or Service Neutral Load." Whereas Article 220 Part II "Branch-Circuit Load Calculations" has nothing comparable.

Therefore the branch circuit neutral load is always considered to be equal to the ungrounded conductor load, and is protected from overload by the OCPD, just like the ungrounded conductors. While a feeder or service neutral may be smaller than the ungrounded conductors, and is protected from overload only by the section 220.61 computation.

Correct?

Cheers, Wayne
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210.19(A)(3) Exception somewhat shoots that in the foot..... it does not apply to dryers but does show the neutral ona branch circuit does not always have to be sized by the ungrounded conductors.
 
I stand corrected; the downsized neutral is not currently acceptable for a branch circuit.

In no case could a neutral smaller than #10 be used for a 30A dryer, because of the requirement of the #10 EGC.

But consider a 50A circuit that has a 20A neutral load.

You could not run a 50A branch circuit using two #8 hots a #10 EGC and #10 neutral. (Some 75C wiring method)

But you could run a 50A _feeder_ with 2x8-2x10.

What happens if this 50A feeder goes to a panel with a single double pole breaker in it?

-Jon
 
LarryFine said:
The control wiring may be allowed to be smaller, but the branch circuit's grounded conductor must be able to be protected from overload by the same OCPD as that which protects the 50-amp conductors.
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What is going to overload it when the only load is a contactor coil and maybe limited number of control relays or timers that also part of the circuit controlling the contactor coil?

Minimum size for a feeder makes some sense, particularly if supplying a panelboard where it might be pretty easy to add more branch circuits. with a fixed load I suppose one could even run say 16, 18, 20 AWG neutral for that contactor coil, though I likely run 14 AWG 99+% of the time. If totally my design I probably use same voltage as motor voltage for said contactor coil, but sometimes I have to deal with whatever equipment vendors supply things with. Some agriculture equipment sadly still comes with that contactor neutral landed in a lug bolted to the enclosure where they expect you to land an EGC. :poop: I remove that and run a neutral directly to the controller.
 
augie47 said:
210.19(A)(3) Exception somewhat shoots that in the foot..... it does not apply to dryers but does show the neutral ona branch circuit does not always have to be sized by the ungrounded conductors.
Click to expand...

Yes that is the exception for a range but notice that the neutral is still sized for the required equipment grounding conductor which is #10
 
augie47 said:
210.19(A)(3) Exception somewhat shoots that in the foot..... it does not apply to dryers but does show the neutral ona branch circuit does not always have to be sized by the ungrounded conductors.
Click to expand...
Which kinda supports what I said in post #14.
 
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