2014 change to 250.122(B)

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Smart $

Esteemed Member
Location
Ohio
Here's what I currently have put together for a proposed revision:

RECOMMEND:
(B) Increased in Size. Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation, wire-type equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of sized according to Table 250.122 based on highest standard overcurrent protection device rating that could be used to protect the ungrounded conductors.

SUBSTANTIATION:
I am uncertain of the premise under which this requirement came into existence, but I see it conflicting with other completely compliant methods.

Consider the following graphic depictions:

Proposed250122Bgraphic.gif


In (A), we have a typical circuit.

In (B), we have ungrounded conductors increased in size to compensate for voltage drop resulting from the circuit length. Under existing requirement, with the overcurrent device rating of 20A, the #12 EGC of the typical circuit must be increased in size proportionately to the increase in size of the ungrounded conductors, resulting in a #6 EGC.

In (C), we used an alternate and compliant method to compensate for the voltage drop, protecting the main run with a 60A overcurrent device, then using an additional 20A overcurrent device at the load end. For this configuration, we are only required to use a #10 EGC.

In (D), we use the proposed revision to size the EGC at #8. Though a #10 is the minimum required in (C), because the ampacity of #6 is 65A@75?C, we could protect the ungrounded conductors with up to a 70A breaker or fuse. This crosses the EGC size threshold in Table 250.122, so a #8 EGC would be required.

In summary, current requirements conflict with the two methods to compensate for voltage drop depicted in (B) and (C) above. If a #10 EGC is sufficient enough to trip a 60A breaker on fault in (C), then a #8 should certainly be sufficient enough to trip a 20A breaker in (D).

Comments...
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
IF we accept that premiss, would a #10 not be sufficient in "D" ?
 

kwired

Electron manager
Location
NE Nebraska
IF we accept that premiss, would a #10 not be sufficient in "D" ?
I say in reality it depends on the available fault current of the source and the total length/size of service/feeders plus the length of the circuit in question, but NEC wants to make it a one size fits all kind of situation, meaning you can have overkill in some instances.

add: I should have thrown in the trip characteristics of the overcurrent device is also an important factor.
 
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Smart $

Esteemed Member
Location
Ohio
IF we accept that premiss, would a #10 not be sufficient in "D" ?
Quite possibly sufficient, but the way I word the revision would require a #8.

An alternative wording would be to use the ampacity of the conductor as the value for determination in Table 250.122... but I'm not quite sure how to word that... and then I think I'd either have to change the table column heading or provide footnotes to clarify. The way I stated the revision was just the easier, less confusing method... and the idea is to get the general idea accepted (or even accepted in principle) by the CMP. If I make the substantiation too hard to comprehend, it'll likely get rejected... good chance it'll get rejected even as is.
 

Smart $

Esteemed Member
Location
Ohio
I say in reality it depends on the available fault current of the source and the total length/size of service/feeders plus the length of the circuit in question, but NEC wants to make it a one size fits all kind of situation, meaning you can have overkill in some instances.

add: I should have thrown in the trip characteristics of the overcurrent device is also an important factor.
Yes, but as you know, Code does not require compensation for voltage drop. And I'm sure you are also aware Code does not require calculation or determination of circuit design falling within the trip characteristics of the OCPD.

So when you look at it from another perspective, you are saying that the circuit depicted in my diagram (C) could be insufficient for the trip characteristics. Ultimately on saying one Code situation may result in overkill, at the same time you are saying another Code situation may result in being insufficient.
 

MasterTheNEC

Host of ElectricianLIVE.com
Location
McKinney, Texas
Occupation
Master Electrician & Director of Codes and Standards
Ok, I am more than sure I am going to ruffle some feathers here but here is my take on this topic.

The proportional increase described in 250.122(B) is clear.

Note that Table 250.122 says "minimum size" and if 250.122(B) increase that size then so be it.

While the general rule of 250.122(A) directs you to T250.66 for the minimum size, if the requirements of 250.122(B) are presented then you will need to increase the size of the EGC accordingly.

The increase is size [given by conditions of 250.122(B)] are based on a reliable return of fault current for the given OCPD.

Just my thoughts on it...
 

MasterTheNEC

Host of ElectricianLIVE.com
Location
McKinney, Texas
Occupation
Master Electrician & Director of Codes and Standards
And I agree with both points. A conductor's ampacity does not change with the length of the run, or with the voltage that is available at the end of the run.


But you do agree that the resistance [impedance] will change based on the length of the run?
 

electricalist

Senior Member
Location
dallas tx
I think it should say it if the egc/ground is good by raceway conduit or any thing else that we can legally use to have a ground.then this circuit or whatever it is must be suplimented with a ground based on ocp. To the last point in which it changes over to something we would have to pull a ground in at that point it shall be size by the ungriunded conductors size until it terminates
 

jap

Senior Member
I think it should say it if the egc/ground is good by raceway conduit or any thing else that we can legally use to have a ground.then this circuit or whatever it is must be suplimented with a ground based on ocp. To the last point in which it changes over to something we would have to pull a ground in at that point it shall be size by the ungriunded conductors size until it terminates

Just my 2 cents, but,

Until someone figures out at what footage the raceway, conduit or anything else, that we legally used as our EGC becomes ineffective,,,, that's going to be a tuff one to figure out where exactly we need to start adding the suplimental Type" EGC to the end.

If the raceway or conduit or whatever we had was an acceptable means of an EGC to begin with,,,,, then there would actually be no need for the supliment.

But then again, most decisions of having to increase the size of the EGC are needed to be made prior to a new installations, more so than an existing one.

<Jap>
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Just my 2 cents, but,

Until someone figures out at what footage the raceway, conduit or anything else, that we legally used as our EGC becomes ineffective,,,, that's going to be a tuff one to figure out where exactly we need to start adding the suplimental Type" EGC to the end.

If the raceway or conduit or whatever we had was an acceptable means of an EGC to begin with,,,,, then there would actually be no need for the supliment.

But then again, most decisions of having to increase the size of the EGC are needed to be made prior to a new installations, more so than an existing one.

<Jap>
When you run the numbers you will find out that steel conduit is suitable for use as an effective EGC in longer lengths than is a code sized EGC of the wire type.
 

Smart $

Esteemed Member
Location
Ohio
When you run the numbers you will find out that steel conduit is suitable for use as an effective EGC in longer lengths than is a code sized EGC of the wire type.
But not necessarily an upsized EGC...

Perhaps electricalist has a point on the conduit being a suitable EGC. Under current code, if you run a wire-type EGC even though not required because the conduit serves as an adequate EGC by itself, we are 'penalized' by having to increase the wire EGC size anyway.
 

Smart $

Esteemed Member
Location
Ohio
...Perhaps electricalist has a point on the conduit being a suitable EGC. ...
Perhaps an easier approach to revision is to just add an exceptionfor a wire-type EGC size as determined with GEMI software analysis (provided to and approved by the AHJ?), but not smaller than in accordance with Table 250.122.

Here's some links on GEMI...

http://steeltubeinstitute.org/steel-conduit/resources/gemi-analysis-research/
https://www.nema.org/Technical/Documents/Bull_97_SteelConduitandEMT-ProventoMeettheNECReg_03_09.pdf
https://www.google.com/search?q=GEMI+grounding+analysis

Any suggestions on Exception wording...???
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
But not necessarily an upsized EGC...

Perhaps electricalist has a point on the conduit being a suitable EGC. Under current code, if you run a wire-type EGC even though not required because the conduit serves as an adequate EGC by itself, we are 'penalized' by having to increase the wire EGC size anyway.

I agree that the installed is penalized but might it not be better to say that if the raceway qualifies as an EGC then we don't really care what size EGC is pulled into the raceway?
 

Smart $

Esteemed Member
Location
Ohio
I agree that the installed is penalized but might it not be better to say that if the raceway qualifies as an EGC then we don't really care what size EGC is pulled into the raceway?
That's why my last post refers to a GEMI analysis approach. Even from what I've read about GEMI analysis, there is a limit to the length of raceway which provides an adequate EGC.

I have not downloaded/installed the GEMI application because I wouldn't use it on my personal computers for anything other than posting here on the forum... which amounts to never installing it on my personal computers. That said, does anyone know if the program provides a grounding analysis for where both raceway and wire-type EGC are used in combination?

PS: I have not yet submitted any proposed revision in this regard. I did submit one regarding the upsizing determination where only AWG sized conductors are involved... amounts to using difference in gauge number rather than actually performing a proportionate cmil cal'.
 
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kwired

Electron manager
Location
NE Nebraska
Ultimately on saying one Code situation may result in overkill, at the same time you are saying another Code situation may result in being insufficient.
Exactly the way it has been for a long time - and other then the presence of a very long run it does provide a safety factor to life and property though it sometimes is overkill.

I have seen many circumstances with long runs on irrigation equipment where overcurrent protection fails to open - most of the time the length of the circuit is likely the reason why, as the same fuse with same fault would open on shorter circuit lengths. Now a bolted fault probably just takes longer but will open overcurrent device eventually, but the fact that 277 volts plus can sustain an arc better then 120 volts, those non bolted faults are also kept from getting too high of a current level just because of the length of the circuit, and often burn out some component instead of blowing fuses.
 

electricalist

Senior Member
Location
dallas tx
That's why my last post refers to a GEMI analysis approach. Even from what I've read about GEMI analysis, there is a limit to the length of raceway which provides an adequate EGC.

I have not downloaded/installed the GEMI application because I wouldn't use it on my personal computers for anything other than posting here on the forum... which amounts to never installing it on my personal computers. That said, does anyone know if the program provides a grounding analysis for where both raceway and wire-type EGC are used in combination?

PS: I have not yet submitted any proposed revision in this regard. I did submit one regarding the upsizing determination where only AWG sized conductors are involved... amounts to using difference in gauge number rather than actually performing a proportionate cmil cal'.
I would think that if a raceway is so long it no longer qualifies as egc someone will have already set another panel sub panel fused disc. Or something. Its not cost effect to run voltage drop wire that far
 

kwired

Electron manager
Location
NE Nebraska
I would think that if a raceway is so long it no longer qualifies as egc someone will have already set another panel sub panel fused disc. Or something. Its not cost effect to run voltage drop wire that far
Sub panel or not the load still draws the same current, so I'm not sure where you want to go with that, you can transform to a higher voltage and then back on the load end, but in many instances cost is less to run larger conductors then it is for a pair of transformers and additional gear necessary to utilize the transformers.

Now if you increase size of your circuit conductors for voltage drop and are using raceway as EGC, you only increase so much and you also will be increasing raceway size as well.
 
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