mshields
Senior Member
- Location
- Boston, MA
If you are going a substantial distance with a feeder such that you have to increase phase conductors for voltage drop, you would never have to increase the Equipment Ground accordingly would you?
250-122 for long feeders
- Thread starter mshields
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shortcircuit2
Senior Member
- Location
- South of Bawstin
Wire Type EGC need to be increased in size proportionately...2020 NEC 250.122(B)
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Yes, and for the same basic reason: impedance, especially under fault conditions.
powerpete69
Senior Member
- Location
- Northeast, Ohio
- Occupation
- Professional Electrical Engineer
If even states that in 250.122(B) 2014 NEC book . Outstanding.
mshields
Senior Member
- Location
- Boston, MA
Ah - true dat yo
RodneyMcDonald
Member
- Location
- Texas
- Occupation
- Electrician
Man, I just typed this same very question! Thank y’all for the answer... great job gentlemen
shortcircuit2
Senior Member
- Location
- South of Bawstin
Well...there is a new twist for 2020...ungrounded conductor increases in size for 310.15(B) ambient correction or 310.15(C) more than 3 current carrying conductors are excluded from the rule. But, increase for voltage drop on long runs would need EGC up-sizing proportionately...well unless (new exception) some qualified person (smaht enginear) can prove otherwise in accordance with 250.4(A)(5) or (B)(4)
Yeah, I got burnt on that one in an inspection years ago.
Wasn’t this already (possibly) the case? Or at least debatably so? Perhaps it is just clarified now. The wording has been something like “...increased in size from the minimum size that has sufficient ampacity for the intended installation...”
I’ve heard reasonable arguments that this means that the ungrounded conductor size you start with are AFTER temp corrections and CCCs in a raceway considerations. Because THAT is the minimum size for the intended installation (or at least that’s what the argument is). Any increase after that adjusted size, such as for VD, would mean an increase in EGC is needed.
Carultch
Senior Member
- Location
- Massachusetts
It was already the case. 2014 and 2017 both specified "minimum size that has sufficient ampacity for the intended installation". I call this the "minimum local size" when working with this rule, the starting point for this calculation. I.e. the size you need, if length were not significant. Bundling adjustment and ambient temperature correction are already factors that apply independent of length.
It helps that it is more directly specified what the calculation is supposed to be, so that the user doesn't need to infer it from several other rules.
Yes, that was my thinking also. Correction factors didn’t need upsizing EGC.
upsizing for VD does.
that’s where the inspector got me..
- Location
- New Jersey
- Occupation
- Journeyman Electrician
That makes sense. If I have 100' run with three #12 (H,N,EGC) conductors or the same 100' run with 30 CCC's the size of the EGC does not need to be increased for the 30 CCC's because it will function the same in either case. This section is revamped just about every code cycle because it's poorly written and difficult to understand, it would be better to just size the EGC according to the ungrounded conductor size. I believe that Don has been pushing that code change for a while and it makes sense. No calcuation required just look at the ungrounded conductor size and size the EGC accordingly.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Seems like with parallel conductors 250.122(B) is not well defined under either the 2017 or 2020 wording. Example:
190A feeder, one conduit, no temperature correction. You could use (3) 250 kcmil Al conductors for a 75C ampacity of 205A. Or you could use (6) 1/0 Al conductors for a 75C ampacity of 192A after the 0.8 adjustment factor. (2) 1/0 conductors have an area of 211.2 kcmil.
So if you choose to use 250 kcmil Al conductors, have the ungrounded conductors been "increased in size"?
Cheers, Wayne
190A feeder, one conduit, no temperature correction. You could use (3) 250 kcmil Al conductors for a 75C ampacity of 205A. Or you could use (6) 1/0 Al conductors for a 75C ampacity of 192A after the 0.8 adjustment factor. (2) 1/0 conductors have an area of 211.2 kcmil.
So if you choose to use 250 kcmil Al conductors, have the ungrounded conductors been "increased in size"?
Cheers, Wayne
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I would say that the 250's have not been increased in size. You chose to run one set (a design choice) and 250's are the minimum size for the 200 amp feeder. Another example of the unneeded complexity of the dumb calculations required. Just size the ungrounded conductors for the feeder and then look on the table for the corresponding EGC. Oh yeah we still can't do that.
Carultch
Senior Member
- Location
- Massachusetts
You likely couldn't parallel in that example, without going out of your way to terminate them in the first place, since most 200A and less equipment is built with the expectation that you'll only use one set. So it would make sense that if you end up using only one set, your starting point in this calculation, is just one set. It would be unreasonable for you to calculate all possibilities of parallel sets, just to find the absolute minimum KCMIL of wire you could use for the amps.
Where it is ambiguous, is in the event that upsizing causes you to increase the number of parallel sets. Consider a 400A circuit with 1x 600 kcmil Cu as your default size. Then you desire to upsize to 2x400 kcmil Cu, to curtail voltage drop. The default size would be 2x3/0 Cu, when you use two sets. So what becomes the upsize ratio? (2*400)/600 = 1.33? Or 2*400/(2*168) = 2.38?
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