Sizing equipment grounding conductors for voltage drop (and other increases). NEC section 250.122(B)

[@timothyruben6621]

I love this channel and the way you break things down very understandably. One thing I recommend though is timestamps in your description so viewers can navigate longer videos like this one to find specific info they may be looking for. Great video! Thanks for your help!

[@ssl3546]

These videos are so interesting. I don't even work in construction and I love watching them.

[@bitsandpeace]

Hi Ryan - I am a new subscriber and I love your channel. I am a retired product design engineer and worked with the UL standard 117. Anyway I do a lot of electrical repair and diagnosis for friends and family on their homes and RVs and solar power systems. I have downloaded the gemi app and love how quick and simple and useful it is. I greatly appreciate your thoroughness and careful approach in all of your videos. I will be promoting you Everywhere! Thank you so much for all you do and I do hope you keep up your great work. Thank You Again!

[@RyanJacksonElectrical]

Thank you!

[@felixsandoval486]

Awesome teaching Ryan, great video, clearer is imposible, excelent content and resources.

[@thomasdupre7882]

Thanks Mr. Ryan Jackson For Your Time.,

[@atomicdmt8763]

outstanding! I appreciate the ATTEMPT to reconcile the (theory) behind the code changes.....

[@porfiriomagana7166]

Phenomenal job on breaking this down buddy, love your channel!!!!!

[@robertochavez8196]

God bless you for sharing your knowledge!

[@davidjackson4112]

Greetings Ryan, Thanks for introducing this software. It sure will be a valuable help. Have a great day.

[@D.Hozzie]

Great explanation Ryan. Thank you.

[@Als4259]

you are very professional Ryan than you so much for your videos .

[@lando6634]

Excellent video!

[@ronaldramirez3256]

Great video, thank you.

[@chicagoflipsters6772]

Thanks for your work . I appreciate . Blessings

[@elc2k385]

Thank you, thank you, thank you.

[@birth23ful]

Can you please do an example of 250.122(B) with parallel circuits? Supposedly FLA=396 BKR=500A By default these could be used: (1)900kcmil | (2)250kcmil | (3)2/0 If due to voltage drop I used (2)350kcmil. Wouldn't all the following be considered minimum size 1*900k=900k or 2*250k=500k or 3*133100=399,300? So can I argue that since circular mil didn't increase 900k>(2*350k=700k) I don't have to proportionally increase my EGC?

[@carultch]

The AWG size scale is defined as a negative logarithmic scale of the cross sectional area in kcmil. This means that an incremental change in AWG is the same thing as a multiplicative change in cross-sectional area. So if you increase your phase conductors by subtracting 4 from the minimum AWG size, you also subtract 4 from the EGC size, and this makes it so you don't even need to look up the KCMIL. Every 3 steps on the AWG scale corresponds to a doubling in kcmil. You will find the occasional rounding errors in the KCMIL-to-AWG tables, that may seem to indicate a larger size than needed when the output of this calculation is just a hair above the nearest standard size. If you use the AWG-to-KCMIL formula instead of the tables, you'll see that you don't need to upsize beyond that.

[@trope5105]

can u xplain this a little bit different.>>/? i dnt know if i get what you were saying

[@carultch]

@@trope5105 Go to en.wikipedia.org/wiki/American_wire_gauge, to get your data. Pick a size, and look for the area in kcmil. I'll use #6 gauge as an example. The area is 26.3 kcmil. Now pick a size that is 3 gauge sizes larger than it. In other words, subtract 3 from the gauge size number above, and look up the corresponding kcmil. For my example, that would be #3 gauge, which is 52.6 kcmil. Compare the two kcmil numbers. Notice that 52.6 kcmil is twice the area of 26.3 kcmil? That's what I mean by "every 3 steps on the AWG scale corresponds to a doubling in kcmil." The unit of kcmil is a unit of cross-sectional area. I'll leave it to you to look up its definition. Try it with other examples, and see if you get the same pattern. Subtracting and adding on the AWG scale, corresponds to multiplying and dividing the kcmil respectively. This is what I mean by "incremental change in AWG is the same thing as multiplicative change in cross-sectional area".

[@carultch]

@@trope5105 Now let's unpack what I mean by negative logarithmic scale. Take the data from the American Wire Gauge table, and paste it into a spreadsheet. Keep only the first column, and the kcmil column. Replace "the aughts" as follows. This is what numbers they would be, if the pattern continued with numbers, instead of renaming them as aught values. 1/0 becomes 0 2/0 becomes -1 3/0 becomes -2 4/0 becomes -3 Make a graph with the kcmil on the horizontal, and the AWG size on the vertical. Compare this with the shape of the graph of the logarithmic function. You'll notice that it looks just like a logarithmic function, except it is negated. Now set the horizontal axis to logarithmic scale. Instead of seeing linear increments between tickmarks, you'll see powers of ten. 1, 10, 100, etc, and on the opposite side, 0.1, 0.01, 0.001 etc (instead of the negative numbers). You also see the logarithmic curve has become a straight line. This shows you that the logarithmic curve, really is a logarithmic function. You've simply compressed the scale on the kcmil, in a format called a logarithmic scale.

[@J-Jim]

After reading the comments... no wonder people have been arguing about 250.122.B for decades! Thank you Ryan, for your insight.

[@chrisf3875]

I must say it is beautifully explained with all sorts of extras.. I'm glad you're not a plumber!! That would have been such a loss to our trade .😉

[@chadgerman8173]

This video was amazing!

[@saidajanane2146]

Love it

[@danilong4353]

Hi sir Ryan. I just happened to see your video today (October 1,2023). It was indeed an I opener for me.. So thankful In deed. Your examples were mainly on residential sizes of circuit breakers.. My question: Is this also applicable for bigger sizes like in switchgear where the size is 1,000 to 2000 ampere? Shall we size our equipment grounding wire at 1000 to 2000 ampere? Would appreciate very much for your kind help.. Thank you..

[@htownelectrican]

👏🏽👏🏽👏🏽

[@paolalicari4439]

Hey Ryan, i follow you on KZbin , great work. You really explain the code great. I have a question on article table 250. 102 C 1 table. The main bonding and system bonding jumpers. How do you size the grounded conductor when all of the largest ungrounded conductor are over 1100 KCmil. Looking forward to seeing your video. Thank you for all that you do.

[@solidus1010]

How do we fit a larger conductor in a 20a breaker for say when we upsize wire size for voltage drop?

[@stevemoore4195]

If I run 2/0 wire from my solar array 400 feet under ground to an 80 amp OCPD and the conductors don’t fit into the OCPD,. Can I downsize the wire to 4AWG using a connector in the panel. And in doing so, can I run a 4AWG ground from the array in the conduit with the 2/0 wires?

[@Tyletoful]

TAKE EVERYTHING IM ABOUT TO SAY WITH A GRAIN OF SALT. THIS IS NOT ELECTRICAL ADVICE PROCEED WITH CAUTION. So first we need to calculate the voltage dropoff of your system, assuming you're running it in copper. The formula 2kil/cma applies here. I chose the k value of 12.9 for copper. With that being calculated. The volts dropped according to my calculations is about 6.2 volts. So if we plug that into ohm's law that tells us that what might come in as 80 amps on one side gets dropped to 75.866 amps on the other. So if I check the ampacity chart located at 310.16 we have a few different categories depending on wire type. If I assume you're in the 90 degree category then we take the number 95 for for the #4 wire's ampacity. However we need to adjust this because it is a constant load. So if I remember correctly we need to multiply this number by .8 because it is a consistent load and that number is 76 amps, which is the ampacity of #4 wire. Which is just slightly higher than the 75.866 amps that would be possible from that OCPD and therefore to code? There could be other rules that I'm just unaware of. Also, I don't know about the rules of a connection of those sorts in a panel, but that's what my math got me to haha, good luck. REMEMBER THIS IS NOT ADVICE, I AM JUST GUESSING IF I WAS IN YOUR SITUATION, HOW ID CALCULATE IT. PLEASE CONSULT A PROFESSIONAL.

[@RyanJacksonElectrical]

You'd have to do the math.

[@JesusCruz-wt2zp]

Nice video.. thanks

[@workct4102]

Let's say I only have a # 8 conductor in my van, for a 30 amp circuit. Do I HAVE to upsize the EGC because I upsized my current carriers? (NEC should say "current carriers instead of ungrounded conductors, because if I increase size for voltage drop I will increase the neutral/grounded conductor as well)

[@RyanJacksonElectrical]

Yes. The argument has long been that increasing the size of the ungrounded conductor yields higher fault current and, therefore, could damage the EGC. So it isn't just a voltage drop issue. Although I'm not convinced, personally.

[@workct4102]

@@RyanJacksonElectrical yeah...it makes no sense seeing as the code specifically states there is NO need to increase EGC for conductor fill or temperature adjustments. Then the EGC is good enough. This code needs to be changed....otherwise I will omit the EGC and use the conduit and be compliant.

[@leodelgado6273]

Ryan, I am up sizing my ground for a 225amp circuit 4/0 to 500MCM do to voltage drop and came up with 1/0? Per table 250.122 the ground size for 500MCM is only #3? Should I use #3?

[@ronaldkovacs7080]

If EMT is used as and EGC, how is the cma of the conduit determined?

[@carultch]

Since the EMT is a different metal entirely than copper, it isn't a 1-for-1 match of cross sectional area to a wire EGC. The Steel Tube Institute has data applicable to the limitations on using conduit as the EGC, in terms of what maximum circuit size they recommend for each trade size, and what maximum length you can effectively count upon the conduit to be the EGC.

[@poolsdoc9178]

I have some doubts with kind of the same issue Ryan, but related with 250.66. We installed a 200 amps service for a barn and we used 350 kcm wire because of the voltage drop. Can you explain to me how would you size the EGC (250.66) . They told me to use #4 solid awg ( I don’t agree) BUT....

[@RyanJacksonElectrical]

We are speaking two different languages here. The EGC is never sized using 250.66. Can you elaborate?

[@poolsdoc9178]

@@RyanJacksonElectrical sorry, I’m talking about the electrode grounding conductor

[@RyanJacksonElectrical]

@@poolsdoc9178 Voltage drop doesn't matter for that, just use 250.66. Don't forget to read (A), (B), and (C) though.

[@poolsdoc9178]

@@RyanJacksonElectrical THANKS! I’ll check it out.

[@wilvenlee2328]

Will the size of EGC reduce also in parallel raceway? what code rule? thanks for your time.

[@RyanJacksonElectrical]

250.122(F) for parallel raceways.

[@wilvenlee2328]

@@RyanJacksonElectrical thank you.

[@jlugolok]

Am I missing something or shouldn’t an increase 402% of 10,380 circular mils equal 52,107.6 and not 41,740?

[@RyanJacksonElectrical]

10.380 x 4.02 = 41,740.

[@jlugolok]

But if your starting value is 10380 and your final value is 41740 then that’s an increase of about 302% 🤔 (41740-10380)/10380 X 100 = 302.12%

[@RyanJacksonElectrical]

@@jlugolok If you increase 10,380 by 100 percent, what do you get?

[@jlugolok]

@@RyanJacksonElectrical Normally I would very confidently say 20,760 but now I’m not too sure 😂

[@jlugolok]

Ah I think I know what happened, 100% increase of 10,380 is 20,760 because you are increasing 10,380 by 10,380. So if we go back to the Initial problem, you would be increasing 10,380 by 41,740 which gives you 52,107.6. If you use 41,740 you would not be taking into consideration that your starting number was 10 awg (10,380). Or am I way off here? Thank you for taking the time to respond by the way.

[@robertgblues5863]

Is the GEMI download for Windows only? Getting nothing but gibberish on my iPad

[@RyanJacksonElectrical]

Not sure, sorry.

[@SuperVstech]

In your HVAC #8 situation, the solution is a fused disconnect... 40A breaker on he #8 wiring at the panel, and a 30A fused disconnect set by the HVAC tech. I do it all the time.

[@RyanJacksonElectrical]

That is debatable. In the 2017 it would not have worked be a use it specifically mentioned the load. Now it doesn't give a starting point (an increase from what??), but one could argue that if the conductors exceed the minimum required for the load they have been increased. This is one of the many problems with this rule.

[@HouRocket713]

May I use the 10 as hot, 8's as neutral/ground?

[@ronaldkovacs7080]

My take on this is the EGC should be large enough should it carry a fault current, the voltage drop along the EGC does not result is a significant voltage above ground on a current carrying exposed part of the unit it is protecting, such as resulting in a stove chassis having a voltage significantly higher that the metal water tap in the kitchen (assuming the plumbing can carry electric current) if somebody should touch both, there is potential for a shock in this conditionl

[@trope5105]

i think youre math was wrong on the second example, unless i forgot how to do math. 10380 Cmills, *402% is 41,727, not 41,740>?? am i wrong? the answer doesnt change, just makin sure im not stupid, im goin through your vids studying for my masters!! thanks a bunch if you reply

[@carultch]

There's rounding errors in the way the table is transcribed. Some numbers round the logarithmic formula for KCMIL up, some numbers round down. If you use the logarithmic formula for AWG instead of the look-up tables, you'll find that the 402% number really "should be" 400%. Until you cross over to sizes above #4/0, where the AWG scale is no longer used, the same number of gauge size increments of the ungrounded wire size, is the same number of gauge size increments of the EGC wire size. You aren't required to let rounding errors govern a design decision on this issue.

[@nhzxboi]

Fun. stuff. The parking lot example. Voltage drop becomes negligible with LED lights. I love real power. Motors!. So abstract...I understand the concept but don't experience the situation at all in design of industrial power circuits. Interesting though. Making me think. Getting tired of thinking. Need a vacation.

[@robertm.2762]

only God makes easy low ,people always make it so complicated