Proportional Increase of EGC for VD

[synchro]

It appears that 4 #10's would meet the conduit fill requirement. So if you could use that for a MWBC then you could split the 120V loads between the two hots. Not only would that split the load currents between the hots, but their currents would subtract on the neutral. So the voltage drop would be reduced compared to using 3 #10's for a 2-wire 120V circuit.

 

[david luchini]

I understand your point and for the most part agree. However the note I'm quoting is contained within 250.122(B) immediately following the requirement for a proportional increase of the EGC. I can't imagine they would put a note in a section that was completely irrelevant to the parent section.

I can't help but feel like the example I gave above regarding 75 deg. C versus 90 deg. C would be one example that would make sense of this note, even it's the ONLY one.

The explanatory note is telling you that there may be a way to not have to increase your ungrounded conductor size...

If you don't increase your ungrounded conductor size, you don't increase your EGC size.

 

[Jerramundi]

Reread the part in red. Ampacity adjustment and correction requirements have nothing to do with EGCs.

But the section it is contained in is about the EGC. It makes zero sense to have a note that is completely irrelevant to the parent section.
Maybe I'm exploring a note that refers to 1 in a 1,000,000 of circumstances here, but I'm just trying to make sense of it.

 

[wwhitney]

I understand your point and for the most part agree. However the note I'm quoting is contained within 250.122(B) immediately following the requirement for a proportional increase of the EGC. I can't imagine they would put a note in a section that was completely irrelevant to the parent section.

The note is referring to the situation that Charlie B explained. The reason for the note is likely because it has been ambiguous at times whether or not increasing the ungrounded conductor for "ampacity adjustment and correction" triggers the 250.122(B) increase in EGC size. The sentence may also be a holdover from commentary on an earlier version of 250.122(B), the Handbook is not the Code and is not always updated in sync with the Code.

Cheers, Wayne

 

[Jerramundi]

The note is referring to the situation that Charlie B explained. The reason for the note is likely because it has been ambiguous at times whether or not increasing the ungrounded conductor for "ampacity adjustment and correction" triggers the 250.122(B) increase in EGC size. The sentence may also be a holdover from commentary on an earlier version of 250.122(B), the Handbook is not the Code and is not always updated in sync with the Code.

Cheers, Wayne

I wouldn't go as far as to say "The Handbook is NOT the Code."
Maybe the side commentary within the Handbook isn't "the Code," but yea.
However, that's a fair point. The "note" I'm quoting isn't explicitly a code article, but rather more of "author's side commentary."
That's an important distinction.

 

[wwhitney]

Anything in the Handbook that is not part of the NEC itself is an "author's side commentary." It's just usually on point and reflects the consensus view. Not always.

Cheers, Wayne

 

[charlie b]

I'm not talking about NOT increasing the ungrounded conductors.

But that is exactly what the Handbook statement is talking about. Let me try a different approach, this time taking it backwards.

• Bill says, "I know a way that will make it unnecessary to increase the size of the EGC."
• Debbi asks, "How would you do that?"
• Bill says, "By not increasing the size of the ungrounded conductors."
• Debbi says, "But with the wire size we picked, and the insulation system that wire has, and with the adjustment factors applied, the wire does not have enough ampacity to handle the load."
• Bill replies, "So let's pick a wire with a higher-rated insulation system, one rated at 90C. That will allow us to apply the adjustment factor to the larger number in the 90C column. That, in turn, will give us the ampacity we need. So we won't have to increase the ungrounded conductor, and as a result will not need to increase the EGC."
• Debbi says, "Well done my young apprentice."

 

[charlie b]

But the section it is contained in is about the EGC. It makes zero sense to have a note that is completely irrelevant to the parent section.

This is what you are getting wrong. The section is not about the EGC. It's about the ungrounded conductors. It is about making them bigger. If we do that, then we have to do something else. What that something else is need not be discussed right now. You have been asking about the Handbook's note. That note alerts us to the possibility that we might not need to make the ungrounded conductors bigger. That, in turn, would mean that we would not need to do that something else (whatever that something might have been).

 

[Jamesco]

//

But that is exactly what the Handbook statement is talking about. Let me try a different approach, this time taking it backwards.

• Bill says, "I know a way that will make it unnecessary to increase the size of the EGC."
• Debbi asks, "How would you do that?"
• Bill says, "By not increasing the size of the ungrounded conductors."
• Debbi says, "But with the wire size we picked, and the insulation system that wire has, and with the adjustment factors applied, the wire does not have enough ampacity to handle the load."
• Bill replies, "So let's pick a wire with a higher-rated insulation system, one rated at 90C. That will allow us to apply the adjustment factor to the larger number in the 90C column. That, in turn, will give us the ampacity we need. So we won't have to increase the ungrounded conductor, and as a result will not need to increase the EGC."
• Debbi says, "Well done my young apprentice."

Won't do anything for correcting voltage drop though.

.

 

[charlie b]

Won't do anything for correcting voltage drop though.

There was a time when the NEC required an increase in the EGC only when the ungrounded were increased because of voltage drop. Then it was changed to say no matter why you increased the ungrounded. That caused some confusion, in that it didn't say what the starting point was, when you determined whether an increase had taken place. I think the 2020 version finally has this cleared up. If a wire size had to be increased because of a temperature correction factor or because of an adjustment factor (i.e., for too many conductors in a conduit), then you don't have to increase the EGC.

For my part, I can only think of two reasons (other than correction or adjustment factors) for increasing the ungrounded conductor size. One is voltage drop considerations. Then other is, "well, that is all I had in the truck."

 

[wwhitney]

Unusual idea: on a 120V circuit, upsize only the neutral conductor. That helps with voltage drop and doesn't require increasing the size of the EGC. Of course, if the voltage drop on just the ungrounded conductor is already too much, that approach won't work.

Cheers, Wayne

 

[synchro]

Unusual idea: on a 120V circuit, upsize only the neutral conductor. That helps with voltage drop and doesn't require increasing the size of the EGC. Of course, if the voltage drop on just the ungrounded conductor is already too much, that approach won't work.

Cheers, Wayne

The ungrounded conductor and EGC could both be upsized to #10, and the neutral increased to #8 and it would still be lower than 40% conduit fill.
Interesting idea, Wayne.

 

[suemarkp]

The note about not having to increase because of temp requirements may have been an attempt to clarify this situation, but it still muddies the waters:

If you have a 50A branch circuit, and run #6 cu for it, most would think that is normal.
But if the source and destination terminations are rated 75C, you could use 75C rated #8 cu for that 50A circuit.
So if #8 cu is acceptable, is #6 oversized and therefore requires a larger EGC? That would be a pain if using NM or MC cable.

So this whole section of 250.122 does not tell you what is the baseline when determining when a wire is oversized. Makes it hard to know if you have upsized or not. I would argue the 60C column is the baseline when under 100 amps. Going larger than that requires upsizing the EGC unless the larger conductors were chosen because of bundling or ambient temp derating.

Charlie's explanation makes sense -- that upsizes due to bundling/ambient conditions don't trigger the upsizing of the EGC. And that is logical because impedance of the EGC (and ungrounded conductor) will be what throttles how quickly the breaker opens on a fault. Circuit length is typically what affects that (and also affects voltage drop). If a circuit in a cold area will trip the breaker quickly enough, so will the same size conductors in a hot area. Oversized conductors because of ambient heat only should not cause the EGC to need to be upsized since the cold circuit with smaller wires would work fine from tripping a breaker. Only length (which causes voltage drop) should matter, and possibly the number of splices.

 

[Jamesco]

So this whole section of 250.122 does not tell you what is the baseline when determining when a wire is oversized. Makes it hard to know if you have upsized or not. I would argue the 60C column is the baseline when under 100 amps. Going larger than that requires upsizing the EGC unless the larger conductors were chosen because of bundling or ambient temp derating.

250.122 (B) Increased in size.

 

[Jerramundi]

But that is exactly what the Handbook statement is talking about. Let me try a different approach, this time taking it backwards.

• Bill says, "I know a way that will make it unnecessary to increase the size of the EGC."
• Debbi asks, "How would you do that?"
• Bill says, "By not increasing the size of the ungrounded conductors."
• Debbi says, "But with the wire size we picked, and the insulation system that wire has, and with the adjustment factors applied, the wire does not have enough ampacity to handle the load."
• Bill replies, "So let's pick a wire with a higher-rated insulation system, one rated at 90C. That will allow us to apply the adjustment factor to the larger number in the 90C column. That, in turn, will give us the ampacity we need. So we won't have to increase the ungrounded conductor, and as a result will not need to increase the EGC."
• Debbi says, "Well done my young apprentice."

I'm not in disagreement with the logic you're using here. If I'm interpreting what you're saying correctly, it's the same logic I'm using for my interpretation of the Handbook Note.

I'm basically saying the same thing you are here - That if you start with 75C ungrounded conductors, upsize them due to voltage drop, but instead of proportionately increasing the EGC as required by 250.122(B) Increased Size, you simply use an EGC of a higher temperate rating (i.e. 90C column).

Where we seem to be in disagreement is whether or not this particular note and the above logic applies to the EGC.

 

[Jerramundi]

This is what you are getting wrong. The section is not about the EGC. It's about the ungrounded conductors. It is about making them bigger. If we do that, then we have to do something else. What that something else is need not be discussed right now. You have been asking about the Handbook's note. That note alerts us to the possibility that we might not need to make the ungrounded conductors bigger. That, in turn, would mean that we would not need to do that something else (whatever that something might have been).

I'm having a hard time agreeing with this. I'm not saying I'm definitively correct. I came to you all for help and I do appreciate all the input. However, to say that a note contained with 250.122(B) is "about the ungrounded conductors" and not about the EGC seems iffy to me. Given the parent section it is contained in, I would argue it's about the EGC, but premised/conditional upon circumstances regarding the ungrounded conductors.

For example, if I go to a 600 section about Disconnect Location that makes certain requirements premised on the existence of an external controller such as a timer, that section isn't about the timer. It's about Disconnect Location. It's just premised on the circumstance of there being an external controller.

 

[david luchini]

proportionately increasing the EGC as required by 250.122(B) Increased Size,

The Code requires this.

you simply use an EGC of a higher temperate rating (i.e. 90C column).

The Code does not permit this.

 

[Carultch]

For my part, I can only think of two reasons (other than correction or adjustment factors) for increasing the ungrounded conductor size. One is voltage drop considerations. Then other is, "well, that is all I had in the truck."

Other examples:
1. Equipment has a minimum lug capacity that requires you to use a larger wire than otherwise necessary for NEC ampacity.
2. You sized for the 60C rating, unaware that the equipment on both sides was listed otherwise for 75C.
3. You didn't bother to take credit for the next size up rule, 240.4(B). Maybe your conductors are in-series with transformer secondaries, where 240.4(B) isn't allowed to apply, and it makes more sense to standardize.
4. You've sized with future use in mind (e.g. full 300A, but are only using 225A at the time of construction). #4 Cu would be good as the EGC for when you do come back later and use the full 300A. But you are currently building with 300A of wire on a 225A circuit, so it appears to be an upsizing.

 

[Jerramundi]

The Code does not permit this.

As pointed out by WWhiteny that these notes are not explicitly part of the actual code, I'm inclined to agree, but for that reason and that reason alone.

I do however appreciate the input and the attempt to make the conclusion concise for both myself and future readers of the thread.

 

[kwired]

//


Won't do anything for correcting voltage drop though.

.

Which is what the topic of discussion is about. The commentary is mostly pointing out there can be occasions where the "normal" size conductor before considering voltage drop may be different sized depending on conductor insulation, but voltage drop has nothing to do with insulation and a lot to do with amount of cross sectional area of the conductor.

Take a 6 AWG NM cable that must use 60C ampacity table - it can only be used for 55 amps but can be protected at 60. 60 amps OCPD means 10 AWG minimum EGC

Now use THHN/TWWN-2 that can be used at 65 amps for 75C and you still have same size conductor but higher ampacity. Could be on a 70 amp breaker but that would mean minimum EGC is now #8.

If you increase conductor size in either situation because of voltage drop you will be increasing EGC proportionally.