EGC

[don_resqcapt19]

In the case of the EGC it's required to be larger than the ungrounded parallel conductors when situations like the one in this thread is encountered. I agree with you that when using a SSBJ the conductor is typically smaller than the a similarly required EGC which makes no sense. Until the NEC comes up with a better rule for EGC's we're stuck with what we have.

Yes, the smaller size is not code compliant, but based on Table 250.102(C)(1) should be an effective fault clearing path.

 

[kwired]

But it is. The fault is being feed from both ends of that 1/0 because of its parallel connection to the rest of that phase.

and the return path on EGC is likely going both ways as well. Plus potentially via another path like the metal raceway or some foreign object that was the reason for the fault in the first place.

 

[steve66]

CMP-5's opinion is that the phase conductor for parallel sets is the sum of the areas of all of the conductors that are connected in parallel, so the EGC for a single set of parallel conductors may be larger than the ungrounded conductors in each raceway.

Ok, but now that I read 250.122 again it says: "but in no case shall they be required to be larger than the circuit conductors supplying the equipment."

If circuit conductors means the sum of the areas, wouldn't "they" mean the sum of the areas of the grounding conductors? If that's the case, we are essentially back to the same thing: each ground wire doesn't have to be any larger than it's corresponding phase conductor.

If that's not what it means, and "they" means each individual grounding conductor, then each grounding conductor doesn't have to be larger than the sum of all the phase conductors. That would be useless exception that would never come into play, and it would be a waste of ink.

Using our example of 10 sets of 3/0 for a 2000 amp service, that would be saying each ground conductor doesn't have to be larger than 10* 3/0 which is 1678 KCM. When we only need a 250 KCM.

Using the other example, 24 sets of 600 KCM for a 4000 amp service, we basically need 10 sets for a 4000 ampacity. We have 24 sets, so we have (more or less) made the phase conductors 2.4 times as larger as they need to be - 24*600 = 14400 KCM. So the exception is saying our ground wires doesn't have to be larger than 14400 KCM, while the calculation basically gives a 500 KCM * 2.4 = 1200 KCM.

It doesn't take long to figure out the ground wire always starts smaller, and we increase it by the same amount as the phase conductors, there just isn't any way for the ground wire to get larger than the sum of the areas of all the conductors connected in parallel.

So it has to be one or the other: Either the ground wire doesn't have to be larger than any individual phase conductor, or we have an exception that might as well be deleted from the code.

 

[ggunn]

Well, right about 6 min and 30 sec, Mike says the equipment grounding conductor doesn't have to be larger than the phase conductor. But right about the end, someone else says the grounding conductor may have to be large than the phase conductors, then there seems to be some discussion about what actually got put in the code right as the video ends.

So I don't think its cut and dry by any means. To me it says what it says, and it says it doesn't have to be larger than the phase conductors "in any case".

I think you guys are confusing the case where the phase conductors are for different circuits with the case where they are parallel sets. When they are parallel sets there is a single OCPD on all of them that has to be able to clear a fault, so when there are many sets the grounding conductor can be required to be larger than the individual phase conductors.

 

[wwhitney]

Ok, but now that I read 250.122 again it says: "but in no case shall they be required to be larger than the circuit conductors supplying the equipment."

That's the 2017 text. The corresponding 2020 text is "The equipment grounding conductor shall not be required to be larger than the circuit conductors supplying the equipment."

If that's not what it means, and "they" means each individual grounding conductor, then each grounding conductor doesn't have to be larger than the sum of all the phase conductors. That would be useless exception that would never come into play, and it would be a waste of ink.

It does come into play with tap conductors, where the EGC is still sized with respect to the OCPD ahead of the taps.

Cheers, Wayne

 

[kwired]

I think you guys are confusing the case where the phase conductors are for different circuits with the case where they are parallel sets. When they are parallel sets there is a single OCPD on all of them that has to be able to clear a fault, so when there are many sets the grounding conductor can be required to be larger than the individual phase conductors.

But until you have more than maybe 3 or 4 conductors in parallel, the minimum required EGC likely isn't larger than the individual parallel conductors, which IIRC this is what the situation was for OP.

 

[steve66]

That's the 2017 text. The corresponding 2020 text is "The equipment grounding conductor shall not be required to be larger than the circuit conductors supplying the equipment."


It does come into play with tap conductors, where the EGC is still sized with respect to the OCPD ahead of the taps.

Cheers, Wayne

Actually, I was on the 2011, but the 2017 is probably the same.

In 2020, they also got rid of the "in any case" phrase.

I was thinking about this some more after reading the 2020 text, and I came to the same conclusion you mentioned. The exception comes into play for tap conductors where the phase conductor size is smaller than usual for the OCP size in table 250.122. For example, a #8 tap on a 400A circuit only needs a #8 equipment grounding conductor.

 

[ggunn]

But until you have more than maybe 3 or 4 conductors in parallel, the minimum required EGC likely isn't larger than the individual parallel conductors, which IIRC this is what the situation was for OP.

I get that, but someone was saying that the grounding conductor will never have to be larger than the phase conductors, which is not true for parallel sets if he was talking about the individual phase conductors in a set. That language is referring to single (as in not part of a parallel set) phase conductors upsized for voltage drop.

 

[don_resqcapt19]

Ok, but now that I read 250.122 again it says: "but in no case shall they be required to be larger than the circuit conductors supplying the equipment."

If circuit conductors means the sum of the areas, wouldn't "they" mean the sum of the areas of the grounding conductors? If that's the case, we are essentially back to the same thing: each ground wire doesn't have to be any larger than it's corresponding phase conductor.

If that's not what it means, and "they" means each individual grounding conductor, then each grounding conductor doesn't have to be larger than the sum of all the phase conductors. That would be useless exception that would never come into play, and it would be a waste of ink.

Using our example of 10 sets of 3/0 for a 2000 amp service, that would be saying each ground conductor doesn't have to be larger than 10* 3/0 which is 1678 KCM. When we only need a 250 KCM.

Using the other example, 24 sets of 600 KCM for a 4000 amp service, we basically need 10 sets for a 4000 ampacity. We have 24 sets, so we have (more or less) made the phase conductors 2.4 times as larger as they need to be - 24*600 = 14400 KCM. So the exception is saying our ground wires doesn't have to be larger than 14400 KCM, while the calculation basically gives a 500 KCM * 2.4 = 1200 KCM.

It doesn't take long to figure out the ground wire always starts smaller, and we increase it by the same amount as the phase conductors, there just isn't any way for the ground wire to get larger than the sum of the areas of all the conductors connected in parallel.

So it has to be one or the other: Either the ground wire doesn't have to be larger than any individual phase conductor, or we have an exception that might as well be deleted from the code.

Take it up with CMP 5...I have without success and the comment that the phase conductor size is the sum areas of all of the conductors in parallel comes from their panel statement on proposals to this section.

 

[infinity]

Take it up with CMP 5...I have without success and the comment that the phase conductor size is the sum areas of all of the conductors in parallel comes from their panel statement on proposals to this section.

Don,
Haven't you submitted PI's to change T250.122 to be based on the conductor size not the OCPD size?

 

[don_resqcapt19]

Don,
Haven't you submitted PI's to change T250.122 to be based on the conductor size not the OCPD size?

I have submitted PIs to change things in 250.122, but did not generate the one that would have changed the sizing of the EGC to be based on the size of the ungrounded conductor. That made it through the first draft in the 2020 code cycle, but there are a lot of other changes that would need to be made in Article 250 and throughout the code to make that work, so it did not make it into the code. Not sure why it did not come back for the 2023. Well, maybe it did, but was resolved at the first draft part of the process, and I did not look at all of the resolved PI.

 

[steve66]

Take it up with CMP 5...I have without success and the comment that the phase conductor size is the sum areas of all of the conductors in parallel comes from their panel statement on proposals to this section.

Don;

I think I get it now. The exception actually comes into play for smaller tap conductors. Not for parallel sets where the phase conductors are upsized.

And I think the 2020 wording is better than the older version I was reading.