NEC 2014 Section 110.14(C)(1)

[augie47]

The wording has changed slightly over the Code cycles. A t one time, I believe, it said 'for voltage drop' but in the '17 it's' just if increased' so in that Code the answer to your question is "yes".

 

[LarryFine]

As of 2014, the NEC used the language, "the minimum size that has sufficient ampacity for the intended installation" to define the starting point for the 250.122(B) calculation.

Then I would posit that the "intended installation" was a 50a range circuit, and someone decided to go with a gas range later.

The #10 EGC in the 6-3 NM is more than adequate for a 15a breaker. After all, that wasn't the "intended installation".

 

[hhsting]

As of 2014, the NEC used the language, "the minimum size that has sufficient ampacity for the intended installation" to define the starting point for the 250.122(B) calculation. This is an improvement over previous editions, but still has some ambiguity. One particular point of ambiguity it leaves, is how to identify the starting point of the calculation, when your upsizing method involves increasing the number of sets in parallel.

This means that if temperature correction and bundling adjustments were the reason for increasing in size, these increases do not govern an increase in the EGC. The intention of 250.122(B) is to apply when you increase in size for curtailing voltage drop. The underlying physics behind this, is that the EGC needs to have enough conductance to be an effective ground-fault current path. Significant lengths reduce its conductance, and so it was indexed to voltage drop upsizing to specify when and how it has to happen. This way, inspectors can look at the circuit as it was built, without having to Ohm-meter the EGC, measure a length, or try to infer what a designer's/installer's intentions were, as to why they upsized it.

The unintended consequence is that the language also tells you to upsize the EGC, in other examples where you might install larger-than-necessary ungrounded conductors. The following are some examples:
#1: "That's what we had on the truck that day", or "that's what we had left over from a previous job".
#2: Unifying on the larger size, to simplify the material inventory. Such as what you might do, if you have 9x 60A circuits and 1x 40A circuit.
#3: Uncertainty about what the terminal temperature rating is, and assuming 60C for worst-case-scenario. Turns out, the equipment is rated for 75C terminations.

What you say is not so. So lets say you are doing voltage drop and now you have phase conductor size X from voltage drop.

Now in order to increase EGC size per NEC 2014 section 250.122(B) you have to take ratio of areas H = (X/Y)*Z where X is area increase phase conductor from voltage drop, Y is the intended area of conductor Without voltage drop and Z is the intended equipment ground conductor area and size based on breaker size Table 250.122, H is the new EGC size

You see the Y intended size depends on breaker size and ampacity table 310 but in ampacity table there are temperature rating. So then are those temperature rating equipment/terminal ratings? If yes then there you have it depends on temperature rating of terminal/equipment. If no then what are they temperature rating of? In my case Y sizing is question breaker is 50A and temperature rating is Not know but 110.14(C)(1)(a) says to use default 60C but then designer says he also does not know and 75C equipment/terminal rating can be used.

 

[Carultch]

What you say is not so. So lets say you are doing voltage drop and now you have phase conductor size X from voltage drop.

Now in order to increase EGC size per NEC 2014 section 250.122(B) you have to take ratio of areas H = (X/Y)*Z where X is area increase phase conductor from voltage drop, Y is the intended area of conductor Without voltage drop and Z is the intended equipment ground conductor area and size based on breaker size Table 250.122, H is the new EGC size

You see the Y intended size depends on breaker size and ampacity table 310 but in ampacity table there are temperature rating. So then are those temperature rating equipment/terminal ratings? If yes then there you have it depends on temperature rating of terminal/equipment. If no then what are they temperature rating of? In my case Y sizing is question breaker is 50A and temperature rating is Not know but 110.14(C)(1)(a) says to use default 60C but then designer says he also does not know and 75C equipment/terminal rating can be used.

X = installed size of the ungrounded concuctors
Y = minimum size of ungrounded conductors for ampacity reasons alone
Z = minimum size of the EGC, if size Y conductors were installed
H = required EGC

Are you trying to tell me, that Y can be the size of the 60C sizing, even if you end up having 75C terminations?

In your example, Y corresponds to #6 Cu and 26.3 kcmil, until we know otherwise that we can use 75C terminations. My understanding is that 75C terminations on both sides, would then revise the value of Y, so it corresponds to #8 Cu and 16.5 kcmil. What am I missing? Is there a particular language that tells you that Y can continue to correspond to #6 Cu in this example, if it is convenient for your calculation?

 

[hhsting]

X = installed size of the ungrounded concuctors
Y = minimum size of ungrounded conductors for ampacity reasons alone
Z = minimum size of the EGC, if size Y conductors were installed
H = required EGC

Are you trying to tell me, that Y can be the size of the 60C sizing, even if you end up having 75C terminations?

In your example, Y corresponds to #6 Cu and 26.3 kcmil, until we know otherwise that we can use 75C terminations. My understanding is that 75C terminations on both sides, would then revise the value of Y, so it corresponds to #8 Cu and 16.5 kcmil. What am I missing? Is there a particular language that tells you that Y can continue to correspond to #6 Cu in this example, if it is convenient for your calculation?

Does not NEC 2014 Section 110.14(C)(1)(a) say default would be 60C if not know less 100A circuits? Am I missing something?

 

[Carultch]

You see the Y intended size depends on breaker size and ampacity table 310 but in ampacity table there are temperature rating. So then are those temperature rating equipment/terminal ratings? If yes then there you have it depends on temperature rating of terminal/equipment. If no then what are they temperature rating of? In my case Y sizing is question breaker is 50A and temperature rating is Not know but 110.14(C)(1)(a) says to use default 60C but then designer says he also does not know and 75C equipment/terminal rating can be used.

Y depends on several different factors. Think of it as the size that the circuit could be, if its length were negligible that you didn't need to think about voltage drop. OCPD can govern the size of Y, conditions of use factors can govern the size of Y, terminations can govern the size of Y.

 

[hhsting]

Y depends on several different factors. Think of it as the size that the circuit could be, if its length were negligible that you didn't need to think about voltage drop. OCPD can govern the size of Y, conditions of use factors can govern the size of Y, terminations can govern the size of Y.

I have voltage drop and I get new size X. Ok so you agree size of Y depends on terminations.

Now since I have voltage drop I do NEC 2014 Section 250.122(B) New EGC: H = (X/Y)*Z

What I am saying is size of new EGC second sentence above depends on Y which then does depend on terminations. So as a result in the end 250.122(B) size DOES depend on temperature rating

 

[Carultch]

I have voltage drop and I get new size X. Ok so you agree size of Y depends on terminations.

Now since I have voltage drop I do NEC 2014 Section 250.122(B) New EGC: H = (X/Y)*Z

What I am saying is size of new EGC second sentence above depends on Y which then does depend on terminations. So as a result in the end 250.122(B) size DOES depend on temperature rating

So help me understand. Where is it that we disagree? My post #19 acknowledged all of that.

 

[hhsting]

This means that if temperature correction and bundling adjustments were the reason for increasing in size, these increases do not govern an increase in the EGC.

Please see above post #19 when you say temperature correction and bundling adjustment you also mean temperature rating/terminations/equipment or not?

 

[Carultch]

Does not NEC 2014 Section 110.14(C)(1)(a) say default would be 60C if not know less 100A circuits? Am I missing something?

It does. But this rule is more academic, than practical.

It applies when you are taking an exam, and it is a formality that always technically applies without proof otherwise. But it rarely governs a design, unless you are using 60C wire, or you are using a type of cable that specifically requires 60C terminations (e.g. NM cable). In practice, more often than not, equipment carries a 75C listing that overrides the default 60C. If 100A and less, the manufacturer has a "burden of proof" to document the product listing to show this, and to label the equipment. If over 100A, 75C is the default.

 

[Carultch]

Please see above post #19 when you say temperature correction and bundling adjustment you also mean temperature rating/terminations/equipment or not?

Different concept.

"Temperature correction and bundling adjustment" refers to Article 310 calculations, that were formerly called derate factors. This is ambient temperature corrections, rooftop temperature adders, and adjustments for qty of wires in a raceway, all of which are applied to the wire temperature rating, as opposed to the equipment terminal rating. If these factors govern an increase in size, this increase doesn't impact the size of the EGC. That increase, also increases the value of Y, in your terminology.

Temperature rating/terminations/equipment, refers to 110.14(C).

 

[Carultch]

So in your one example of just using larger conductors for a circuit because “that’s what the good ol boys had on the truck bed that day” would also govern the EGC to be proportional due to the increase size on UNGROUNDED conductors correct?

Yes, that is my understanding.

 

[hhsting]

Different concept.

"Temperature correction and bundling adjustment" refers to Article 310 calculations, that were formerly called derate factors. This is ambient temperature corrections, rooftop temperature adders, and adjustments for qty of wires in a raceway, all of which are applied to the wire temperature rating, as opposed to the equipment terminal rating. If these factors govern an increase in size, this increase doesn't impact the size of the EGC. That increase, also increases the value of Y, in your terminology.

Temperature rating/terminations/equipment, refers to 110.14(C).

Ok I misunderstood two different concept. No I dont have increase in size from temp correction or bundling.

So are you saying you have to know temperature rating of terminations or equipment. One cannot use default 110.14(C)(1)(a) says if one does not know?

 

[Carultch]

Ok I misunderstood two different concept. No I dont have increase in size from temp correction or bundling.

So are you saying you have to know temperature rating of terminations or equipment. One cannot use default 110.14(C)(1)(a) says if one does not know?

As an unintended consequence to the wording of 250.122(B), and its interaction with 110.14(C), yes, that is what I am saying. That is the conservative/strictest-possible interpretation of this rule. Because replacing 60C eqpt with 75C eqpt, will reduce the "minimum size that has sufficient ampacity" as you take credit for the higher termination temperature. If anyone has information to the contrary of this interpretation, please enlighten us.