Minimum Size Grounded Conductor for a Branch Circuit

[Dennis Alwon]

I think Charlie may have the answer.

Bob I couldn;t think of a real life situation but let's look at a dryer. The neutral conductor is used for a motor that is rated under 20 amps at 120V. The dryer calls for 240V 30 amps so the egc is #10. I was told that the neutral could be sized for the 20 amps. I didn't believe it could be but that was my question--

There is also section 210.19(A)(3) that allows the neutral to be smaller than the range, wall oven, etc but never smaller than #10 which would be the EGC size for a 60 amp circuit.

Thanks again Charlie-- I believe that clears it up.

 

[charlie b]

Am I understanding that right? Just an example above.

I think you would need a #8 EGC for your example, since the extra 25% would require the breaker to be "biggie sized." But still, the neutral would be bigger than the EGC.

 

[Dennis Alwon]

Hypothetically I am running a continuous lighting load of 14 amps to a yard light. My run is pvc and my ungrounded conductor must be sized to 14 * 1.25 = 17.5 amps. Now I need a 20 amp breaker with #12 wire. According to article 210.19(A)(1) exception #2 I can size my grounded conductor at 100% of the load. This means I could have a #14 neutral with a #12 egc on a 20 amp breaker. Yes? Sounds wrong but it looks like it is code compliant.

 

[charlie b]

Yes? Sounds wrong but it looks like it is code compliant.

Yes. Good example. But I would observe that the ampacity of the #14 neutral is actually 25 amps (presuming you used THHN). So I would not be concerned about its ability to conduct enough fault current, in the event of a L-N fault, to cause the breaker to trip.

 

[Dennis Alwon]

Yes. Good example. But I would observe that the ampacity of the #14 neutral is actually 25 amps (presuming you used THHN). So I would not be concerned about its ability to conduct enough fault current, in the event of a L-N fault, to cause the breaker to trip.

Geez Charlie, so why do we have a #12 EGC in 12/2 NM cable and not #14? At some point it must make a difference. Anyway my point was that I was surprised there wasn't a code section for branch circuits that specifies the grounded conductor cannot be smaller than the egc.

 

[iwire]

Hypothetically I am running a continuous lighting load of 14 amps to a yard light. My run is pvc and my ungrounded conductor must be sized to 14 * 1.25 = 17.5 amps. Now I need a 20 amp breaker with #12 wire. According to article 210.19(A)(1) exception #2 I can size my grounded conductor at 100% of the load. This means I could have a #14 neutral with a #12 egc on a 20 amp breaker. Yes? Sounds wrong but it looks like it is code compliant.

IMO 240.4(D) prevents the use of a 14 AWG with a 20 amp breaker in this example.

 

[iwire]

my point was that I was surprised there wasn't a code section for branch circuits that specifies the grounded conductor cannot be smaller than the egc.

I am pretty sure Chris, Charlie and I got your point.


My point, and I think Chris's as well is that you do not need a rule like that for branch circuits as it is not an issue that cam come up.

 

[Dennis Alwon]

IMO 240.4(D) prevents the use of a 14 AWG with a 20 amp breaker in this example.

You may have a point there.

 

[iwire]

If that is the case what purpose does 210.19 except. 2 have?

Maybe nothing.

That is why I was asking if you could give an example as I could not come up with any on my own,

 

[raider1]

I am pretty sure Chris, Charlie and I got your point.


My point, and I think Chris's as well is that you do not need a rule like that for branch circuits as it is not an issue that cam come up.

That is exactly my point.

Chris

 

[Dennis Alwon]

Maybe nothing.

That is why I was asking if you could give an example as I could not come up with any on my own,

Bob I gave an example and on second thought I think 240.4(D) does not apply since that is talking about OCP. The neutral does not directly have OCP on it.

 

[LarryFine]

According to article 210.19(A)(1) exception #2 I can size my grounded conductor at 100% of the load. This means I could have a #14 neutral with a #12 egc on a 20 amp breaker. Yes?

No. It's not a neutral.

 

[iwire]

Bob I gave an example and on second thought I think 240.4(D) does not apply since that is talking about OCP. The neutral does not directly have OCP on it.

But the neutral is protected by the breaker, that is the entire point of the thread is it not?

 

[Dennis Alwon]

But the neutral is protected by the breaker, that is the entire point of the thread is it not?

Yes but with that logic then a feeder neutral would be limit also because of 310.16 and the breaker. No?

 

[Dennis Alwon]

No. It's not a neutral.

Sometimes typing neutral is easier than typing grounded conductor. Sorry you will have to live with my non compliant verbiage.

 

[LarryFine]

Sometimes typing neutral is easier than typing grounded conductor. Sorry you will have to live with my non compliant verbiage.

No slur intended. I meant that a MWBC's shared neutral could be reduced, whereas the grounded conductor of a 2-wire circuit could not.

 

[Dennis Alwon]

No slur intended. I meant that a MWBC's shared neutral could be reduced, whereas the grounded conductor of a 2-wire circuit could not.

Can you help me with that. Where does the code allow that. I also disagree with your last part as I already gave a situation where the grounded conductor of a 2 wire circuit could be reduced--the outdoor lights at 14 amps continuous.

 

[Buck Parrish]

I know that article 215.2(A)(1) states the minimum size grounded conductor for a feeder cannot be smaller than the egc-- next to last paragraph.

My question is where does the NEC state the same for a branch circuit? Logic tells me the grounded conductor must not be smaller than the egc but I cannot find it. Thus if you have a range- can the grounded conductor be a #12 if the egc is #10? I say no but I am being challenged on it and I cannot support my claim. For this situation we will assume a #12 is sufficient for the load.

I was trying to follow along. Thought I would throw out a different perspective.

But (if )14 was okay with 12. But for sure any thing smaller then that is subject to break.
In theory isn't the EGC the most important conductor when considering safety.

 

[Dennis Alwon]

I was trying to follow along. Thought I would throw out a different perspective.

But (if )14 was okay with 12. But for sure any thing smaller then that is subject to break.
In theory isn't the EGC the most important conductor when considering safety.

What I was trying to say was that with a feeder the grounded conductor cannot be smaller than the egc. Why? Because in case of L-G fault or L-N fault the breaker would trip safely. Apparently, there is no rule for that in a branch circuit.

The reality is it would probably never come into play, however, I could see where the could be a piece of equip. that would need a 100 amp breaker but also needs a neutral for a control circuit. In this case we would have to run a full size neutral even though that would be overkill. So why can't we run a calculated neutral for a branch circuit as long as it isn't less than the egc. In this example the neutral could be #8 instead of #3. I am not sure there is any equipment like this example out there.

From there I notice that it was possible, ever so remotely that one might be able to run a smaller grounded conductor then the egc. That sort of defeats the protection of the circuit.

It really isn't a big issue but I thought it was an interesting find. Others didn't think so....

 

[Smart $]

Glancing through the thread I didn't notice anyone mentioned 210.19(A)(4) specifically. It permits conductors to be sized at an ampacity sufficient for the loads served, and does not correlate that permission with any OCP sizing requirements. 240.4(D) would prevent a grounded conductor from being sized smaller than the required circuit OCP, but once above #10 in wire size I do not see any restriction to reducing the grounded conductor which has a lower load than the circuit's ungrounded conductors [except loads listed in 210.2, which have their own conductor sizing requirements, and 210.19(A)(3) mentioned previously].

As you mentioned, and I agree, it is likely a rare situation where one could reduce a neutral conductor's size, but under 210.19(A)(4) it is possible that the neutral conductor could be smaller than the circuit's ungrounded conductors and EGC.