MCA and EGC sizing

[infinity]

Looked at this today. AC unit with MCA=43.9 amps, MaxOCPD=60 amps. Engineer specified #6 THHN in EMT with a #10 EGC. Since #8 THHN is a 50 amp conductor my first assumption was that the EGC has to be up-sized to a #8 when installed with the #6 ungrounded conductors. Thoughts?

 

[stickboy1375]

Looked at this today. AC unit with MCA=43.9 amps, MaxOCPD=60 amps. Engineer specified #6 THHN in EMT with a #10 EGC. Since #8 THHN is a 50 amp conductor my first assumption was that the EGC has to be up-sized to a #8 when installed with the #6 ungrounded conductors. Thoughts?

Yeah, lose the #10 EGC altogether and use the EMT as a grounding conductor. :lol::lol::lol::lol:

 

[curt swartz]

What if some of the terminals in this circuit are only rated for 60C? #6 would be required so the #10 EGC would be ok. If they are all rated for 75C, I agree that the EGC would need to be #8. Makes a lot of sense doesn't it???

 

[Dennis Alwon]

I also agree the EGC needs to be increased but that is the exact issue with this rule. Suppose this was a residence. I would like to use #8 but I can't because #8 NM is rated 60C so I have to go up to #6 NM and I could use the #10 EGC in the cable using a 60 amp OCPD. Now if instead I want to run pvc I would have to upsize the egc to #8 because the specs say I need more than a #8. The current doesn't change but the egc would have to because we would use the 75C rating. :? :thumbsdown:

 

[ptonsparky]

Boils down to the same issues discussed and cussed many times. Sounds like a change order...

 

[suemarkp]

For things rated under 100A, I think you could argue that 60C wiring is the "normal" size (does the circuit breaker know if the insulation is 75C or 60C?). Anything larger than that is upsizing.

 

[Sierrasparky]

For things rated under 100A, I think you could argue that 60C wiring is the "normal" size (does the circuit breaker know if the insulation is 75C or 60C?). Anything larger than that is upsizing.

Unfortunately that is one's interpetation of the rule.
A cost saving contractor would say " the breaker is rated for 75c and the Disco is rated at 75c so anything more expensive is a upgrade." That being said the EGC would need to be upsezed.
As I said in prior rants. This rule is silly. it has a purpose and a place but not in many circumstances. Many - being MOST!

I looked at a 2002 illustrated NEC and it clearly states the intention is for Increase in size due to voltage drop. It is my belief this rule is all about voltage drop and never thoght to impact what we here are dealing with.

 

[infinity]

I found this from the 2014. Maybe some clarification is coming:

5-197 Log #8 NEC-P05
Final Action: Accept
(250.122(B))
________________________________________________________________
Note: This Proposal appeared as Comment 5-181 (Log #2235) which was
held from the A2010 ROC on Proposal 5-290. The Recommendation on
Proposal 5-290 was: Revise text to read as follows:
(B) Increased in Size. Where ungrounded conductors are increased in
size from the minimum size that has sufficient ampacity for the intended
installation, grounding conductors, where installed, shall be increased in
size proportionally according to the circular mil area of the ungrounded
conductors.
Submitter: Technical Correlating Committee on National Electrical Code?,
Recommendation: The Technical Correlating Committee directs that the
action on the comment be reported as ?Hold? consistent with 3.3.1 of the NEC
Style Manual in that it is not written in clear and concise language.
Substantiation: This is a direction from the Technical Correlating Committee
on National Electrical Code Correlating Committee in accordance with 3.4.2
and 3.4.3 of the Regulations Governing Committee Projects.
Panel Meeting Action: Accept
Panel Statement: The panel accepts the direction from the TCC. See Panel
action and statement on Proposal 5-199.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 16
__________________________________

 

[Dennis Alwon]

For things rated under 100A, I think you could argue that 60C wiring is the "normal" size (does the circuit breaker know if the insulation is 75C or 60C?). Anything larger than that is upsizing.

That was what I was saying-- sorta kinda

 

[Dennis Alwon]

I found this from the 2014. Maybe some clarification is coming:

This seems to support what was stated above. Now you would have to use the 60C rating as the minimum. This makes sense since the insulation has no affect on the ability of the conductor to carry the fault, at least not enough to be an issue.

Personally I would like to see an exception that reads-- where a raceway is used that can also be used as a grounding means then no increase is necessary. Why does one have to increase the size of the EGC if they are using emt.

 

[don_resqcapt19]

The best way to fix this code problem would be to make T250.122 work like T250.66. The EGC size would be based only on the size of the largest ungrounded conductor in the circuit. This would eliminate any need for proportional calculations and would get away from the cases where you can upsize the OCPD and use a smaller EGC.

 

[Dennis Alwon]

The best way to fix this code problem would be to make T250.122 work like T250.66. The EGC size would be based only on the size of the largest ungrounded conductor in the circuit. This would eliminate any need for proportional calculations and would get away from the cases where you can upsize the OCPD and use a smaller EGC.

Have you proposed that?

 

[don_resqcapt19]

Have you proposed that?

I haven't but it has been proposed and CMP 5 rejected it.

 

[Sierrasparky]

This seems to support what was stated above. Now you would have to use the 60C rating as the minimum. This makes sense since the insulation has no affect on the ability of the conductor to carry the fault, at least not enough to be an issue.

Personally I would like to see an exception that reads-- where a raceway is used that can also be used as a grounding means then no increase is necessary. Why does one have to increase the size of the EGC if they are using emt.

Dennis where do you read that you must use the 60C rating. If you are using THHN and both ends support 70C connections then the minimum size for a 50 amp circuit would be #8 and if you used # 6 as proposed by the OP then an upsize EGC would be necessary. This would be a legitimate argument.
Why the Code panel can't move away from this type of nonsense is beyond me. If this rule was intended to add safety for long runs then say so in the rule. Make a minimum distance. Also make a starting point from what size EGC you start the upsize from. Not all cables have the same size EGC as others do for the same size CCC as I found in my reading yesterday.

SER cable seems to have larger EGC than necessary. In my opinion SER already has larger EGC.

What is real intent of the authors of this rule. Are they backed by cable manufactures? Wht is the motivation. The corrected language is absurd. The code making body needs to put down on paper what the mean.

Again in the 2002 hanbook ( I don't know who approves it's interpetation) explains this rule as to be applied to Voltage drop conditions.

This rule is getting more nonsense as the days go by. Hear I am complaining about a rule that if corrected will not help me or affect me for 6 years!

Some would say that is insane!

 

[suemarkp]

I'm with Sierra on how he's reading the proposed 2014 language. I interpret the "minimum size" as being the smallest conductor of the highest temperature rating you can use to be the baseline. That could hose a lot of installs forcing you to rip out perfectly good oversized wiring when a more efficient appliance gets replaced. This is totally stupid on things like AC unit whips.

The code in 250.122 used to specifically say "due to voltage drop" and may also have had "or other reasons". So the original intent was on the excessive length and voltage drop idea, but in later versions of the code that has been disappearing.

I'd like to see Don's solution (size by wire size and not breaker size), or put a 200' length minimum on the affected wiring. This still won't prevent stupid, since we have no Vd requirements in the code. Someone could run 1000' of 14-2 and be perfectly compliant and have a circuit that won't trip a breaker on a fault.

 

[Sierrasparky]

I'm with Sierra on how he's reading the proposed 2014 language.
...............
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Someone could run 1000' of 14-2 and be perfectly compliant and have a circuit that won't trip a breaker on a fault.

Yes I think you are correct. You above scenario is what the rule has intended to cure, but has diverged and morphed into something that will make perfectly great jobs illegal. I would bet this is done to:
1) Either force the EC to using that absolute minimum size wire no matter what.
or
2) to create more wire sales.

This rule is nonsense as written. There is a place for proper language as has been offered above although apparently refused.
I think it is time to Flogg those on the panel.

i will quote this that I have read many time from many folks recently.

" It is difficult to get a man to understand something when his salery ( Compensation) depends on his not understaanding it!"
UPTON SINCLAIR..

 

[don_resqcapt19]

...Again in the 2002 hanbook ( I don't know who approves it's interpetation) explains this rule as to be applied to Voltage drop conditions. ...

When this code rule first appeared in the code, it only applied when the conductor was upsized for voltage drop. That proved to be un-enforcable as the inspector had no way of proving that it was upsized because of voltage drop, so that part of the rule was dropped making it apply any time an "oversized" ungrounded conductor is used.
That being said the rule is a mess and needs major work.
As far as the handbook comments they are no more valid than any comment that you would read here. They are not offical comments of the NFPA. They are written by the NFPA paid staff.

 

[Sierrasparky]

When this code rule first appeared in the code, it only applied when the conductor was upsized for voltage drop. That proved to be un-enforcable as the inspector had no way of proving that it was upsized because of voltage drop, so that part of the rule was dropped making it apply any time an "oversized" ungrounded conductor is used.
That being said the rule is a mess and needs major work..

Obsurd, If the run is 100' or 500' then the wire is upsized. Walks like a duck , quacks like a duck, looks like a duck.!!!!!

As far as the handbook comments they are no more valid than any comment that you would read here. They are not offical comments of the NFPA. They are written by the NFPA paid staff.

That may be true, however it is more obsurd than the last statement. The book is put out by the NEC, it is written by the NEC, it ha is NEC stamped all over the cover and inside. Someone needs to take responsibility for their actions. There is a reason the logo is all over the book ,THAT's Because the NEC ENDORSES IT!... We keep playing these games, things are going to get out of hand and someone is going to get hurt!

Sorry for the rant this ridiculousness is going too far. What about the combination AFCI fiasco. Engle has lost his steam.

 

[Dennis Alwon]

Dennis where do you read that you must use the 60C rating.

I did not read that you must use the 60C rating, I inferred it based on this

increased in size from the minimum size that has sufficient ampacity for the intended installation

60C is the minimum size required-- a #4 wire does not care if it has 60C or 90C temp rating for a fault. The capacity of the #4 is really limited because of the temp of the insulation. In theory we should always use the 90C rating but the statement above says the minimum size. I think the changes creates more trouble then it will fix.

I assume the reason we can use smaller conductors for the egc is because the conductors themselves can carry the faults and the insulation should not come into play. Just a thought.

 

[don_resqcapt19]

...That may be true, however it is more obsurd than the last statement. The book is put out by the NEC, it is written by the NEC, it ha is NEC stamped all over the cover and inside. Someone needs to take responsibility for their actions. There is a reason the logo is all over the book ,THAT's Because the NEC ENDORSES IT!... We keep playing these games, things are going to get out of hand and someone is going to get hurt!

Sorry for the rant this ridiculousness is going too far. What about the combination AFCI fiasco. Engle has lost his steam.

There is a specific way to get a formal interpretation and it is processed just like a code change proposal. While the NEC publishes the NEC, the NFPA does not have the authority to issue a formal ruling. That can only be done by the code making panels. As far as I know, no one who is paid by the NFPA, sits on any code making panel.