NECA National Electrical Code Questions - Voltage Drop
Voltage Drop and NECA Question of the Day Response
Back in the early 80s I used to follow a gentleman named Charles Trout. Charlie, as he became known to me as we developed a friendship, was a well-known electrical code expert and author for Electrical Contractor Magazine from 2009 to 2013. However, most folks remember “Charlie” as the face behind the widely popular blog “NECA Question of the Day” found HERE which grew in popularity over the years. While Charlie passed away in 2015, the legacy of his work continues on at NECA as the Question of the Day e-mail subscription and blog have become a staple for most morning coffee lessons.
However, from time to time the questions and answers could use some additional “clarification” for the reader. Here is one case we will discuss.
The question was in regard to the increase in the Equipment Grounding Conductor [EGC] based on the increase in the size of the ungrounded [HOT] conductors. Now, in all fairness, the NECA QOD is not designed to teach a lesson but that is where “WE” come into play. Saying that “Dennis” the author of the question is correct without explaining why he is correct leaves folks wondering “Why Dennis is correct?”.
First, let’s look at what 250.122(B) says from a “Codeologist” point of view.
“(B) Increased in Size.
Equipment grounding conductors shall be permitted to be sized by a qualified person to provide an effective ground-fault current path in accordance with 250.4(A)(5) or (B)(4)
The increase from 12 AWG CU to 6 AWG CU in the question was due to Voltage Drop. Based on 250.122(B) the EGC has to be increased “proportionately” to the increase in circular mil area of the ungrounded [HOT] conductors increase.
To do this you take the newly selected conductor size, in this question, 6 AWG CU, and find its circular mil value which is 26,240 circular mils based on Chapter 9, Table 8.
Taking the newly acquired 26,240 circular mils from Chapter 9, Table 8, the electrician then divides that value into the circular mils of the original conductor size, which is 6,530 circular mils (12 AWG CU) also found in Chapter 9, Table 8.
This results in 26,240 CM / 6.530 CM = 4.01, otherwise known as a 4.01 Ratio.
We all know or should know, that the size of the Equipment Grounding Conductor [EGC] is based on the rating of the “Overcurrent Protective Device” located ahead of the circuit it’s dedicated to protecting. In the original question, Dennis proposed 20 Amps and per Table 250.122 the size of the original EGC would have been 12 AWG CU.
Based on the aforementioned discussion about increasing the EGC proportionally to the increase in the size of the ungrounded [HOT] conductors we use the “Ratio” we created to cover the proportional increase as demanded in 250.122(B).
GIVEN: 6,530 circular mils (the original size of the EGC) x 4.01 (the ratio/proportional increase) equals 26,185.3 circular mils. This is the new minimum size of the EGC based on the rules in 250.122(B), excluding the exception which we will not discuss in this article.
Finally, the code-savvy electrician turns to Chapter 9, Table 8 and now selects a conductor that is equal to or greater than the 26,185.3 circular mils, which results in a 6 AWG CU. This is why the question was stated as “Correct” by NECA.
In conclusion, it should be said that we LOVE the NECA Question of the Day Series and highly recommend everyone who has an interest in the National Electrical Code join the free subscription to their article. Here is a link to get signed up and start learning more about the National Electrical Code- https://neca-neis.org/code-question-of-the-day
I would be remiss if I didn’t inform you that learning how to do “voltage drop” and other electrical calculations is covered in our Fast Trax® Black Course. If any of this was confusing to you then we highly encourage you to join our family and become a Fast Trax® Member today. CLICK HERE to join.