EGC size

[hhsting]

I have 60A fused disconnect which has 60A fuse and it is being fed from #6 awg phase/neutral with #10 awg ground.

Now they are replacing 60 fuse with 30A fuse. Do they have to replace equipment grounding conductor from #10 awg to #6 awg NEC 2017 Article 250.122(B)?

 

[NoahsArc]

I'm not understanding, they are reducing the size of the OCPD and not changing the size of the ungrounded conductors, and the EGC was already to code, so... why would it be increased?

 

[roger]

Well I wouldn't worry about but I guess since you are increasing the ungrounded 30 amp conductors the technically 250.122(B) would mean you would have to increase the EGC the same.

 

[infinity]

I'm not understanding, they are reducing the size of the OCPD and not changing the size of the ungrounded conductors, and the EGC was already to code, so... why would it be increased?

A 30 amp circuit would typically use #10 AWG conductors with a #10 AWG EGC. Since they're using #6 AWG condcutors they've increased the ungrounded conductor size from #10 to #6 bring forth the requirements of 250.122(B).

 

[jap]

They are not increasing the size of the conductors they are reducing the size of the overcurrent protection.

JAP>

 

[wwhitney]

I have 60A fused disconnect which has 60A fuse and it is being fed from #6 awg phase/neutral with #10 awg ground.

Now they are replacing 60 fuse with 30A fuse. Do they have to replace equipment grounding conductor from #10 awg to #6 awg NEC 2017 Article 250.122(B)?

Under the 2017 NEC, yes, stupidly.

Well I wouldn't worry about but I guess since you are increasing the ungrounded 30 amp conductors the technically 250.122(B) would mean you would have to increase the EGC the same.

2020 NEC added the exception to 250.122(B) that says:

"Exception: Equipment grounding conductors shall be permitted to be sized by a qualified person to provide an effective ground fault current path in accordance with 250.4(A)(5) or (B)(4)."

IMO, this permits the installer or designer to say "I am qualified, I know the #10 EGC provided an effective ground fault current path when the disconnect had 60A fuses (this is a judgement, if the conductor run was long enough that may not be true), therefore it still provides an effective ground fault current path with 30A fuses."

Cheers, Wayne

 

[infinity]

2020 NEC added the exception to 250.122(B) that says:

"Exception: Equipment grounding conductors shall be permitted to be sized by a qualified person to provide an effective ground fault current path in accordance with 250.4(A)(5) or (B)(4)."

IMO, this permits the installer or designer to say "I am qualified, I know the #10 EGC provided an effective ground fault current path when the disconnect had 60A fuses (this is a judgement, if the conductor run was long enough that may not be true), therefore it still provides an effective ground fault current path with 30A fuses."

This code sections changes about every two code cycles because they cannot seem to get it right. It amazes me that the CMP actually put this language in the NEC. It's time for term limits for CMP members.

 

[wwhitney]

They are not increasing the size of the conductors they are reducing the size of the overcurrent protection.

The text of 2017 250.122(B) starts off "Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation . . ." Here "increased in size" just means "larger." When the minimum size that has sufficient ampacity goes down in size, if the ungrounded conductors down also go down in size, the ungrounded conductors are now "increased in size."

Cheers, Wayne

 

[wwhitney]

It amazes me that the CMP actually put this language in the NEC.

What do you have against the language in 2020 NEC 250.122(B) Exception? It provides flexibility for a situation like the OP, flexibility that was missing in the 2017 NEC.

Cheers, Wayne

 

[jap]

The text of 2017 250.122(B) starts off "Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation . . ." Here "increased in size" just means "larger." When the minimum size that has sufficient ampacity goes down in size, if the ungrounded conductors down also go down in size, the ungrounded conductors are now "increased in size."

Cheers, Wayne

They did not increase the size of the existing conductors, they reduced the size of the overcurrent protection.

Two different things.

JAP>

 

[jap]

There's a difference between pulling in conductors and changing a fuse in my book.

JAP>

 

[wwhitney]

They did not increase the size of the existing conductors, they reduced the size of the overcurrent protection.

Evaluating the new changed installation against the previous installation is not part of the equation. You evaluate against an installation that uses the minimum size ungrounded conductor that has sufficient ampacity.

I.e. the baseline is pulling out the conductors and putting in 30A fuses and 30A conductors. The baseline is not the previous installation.

Cheers, Wayne

 

[infinity]

What do you have against the language in 2020 NEC 250.122(B) Exception? It provides flexibility for a situation like the OP, flexibility that was missing in the 2017 NEC.

Cheers, Wayne

The language is ambiguous at best. A qualified person? I know we've discussed that definition before but it's becoming comical the way they've re-written 250.122(B) over and over again. And why no exception for a metal raceway that already qualifies as an EGC or do we
invoke the qualified person rule on that one too?

 

[jap]

If you were increasing the ungrounded conductor size prior to the pull of a certain amperage I could see where the EGC would need to be increased.

Evaluating the new changed installation against the previous installation is not part of the equation. You evaluate against an installation that uses the minimum size ungrounded conductor that has sufficient ampacity.

I.e. the baseline is pulling out the conductors and putting in 30A fuses and 30A conductors. The baseline is not the previous installation.

Cheers, Wayne

The rule states "When ungrounded conductors are INCREASED".

They didn't increase the size of the conductors.

The existing conductors are of sufficient size to carry the load, so, there was no need to increase the size of them.

JAP>

 

[wwhitney]

And why no exception for a metal raceway that already qualifies as an EGC or do we invoke the qualified person rule on that one too?

The base rule in 250.122(B) only covers wire-type EGCs, so there's no reason to discuss other EGCs in the exception.

When running a wire type EGC and a raceway EGC, I do think that if a qualified person judges that the raceway EGC provides an effective ground fault current path, then the Exception can be invoked to negate the need to upsize the wire-type EGC, if that would otherwise be necessary under 250.122(B).

Cheers, Wayne

 

[roger]

Under the 2017 NEC, yes, stupidly.


2020 NEC added the exception to 250.122(B) that says:

"Exception: Equipment grounding conductors shall be permitted to be sized by a qualified person to provide an effective ground fault current path in accordance with 250.4(A)(5) or (B)(4)."

IMO, this permits the installer or designer to say "I am qualified, I know the #10 EGC provided an effective ground fault current path when the disconnect had 60A fuses (this is a judgement, if the conductor run was long enough that may not be true), therefore it still provides an effective ground fault current path with 30A fuses."

Cheers, Wayne

I know and am aware of the 2020 changes but was addressing the OP's specifically asking about the 17.

 

[hhsting]

If you were increasing the ungrounded conductor size prior to the pull of a certain amperage I could see where the EGC would need to be increased.


The rule states "When ungrounded conductors are INCREASED".

They didn't increase the size of the conductors.

The existing conductors are of sufficient size to carry the load, so, there was no need to increase the size of them.

JAP>

Kind of wonder why we even have this rule. I mean if you lower the overcurrent protection size like in OP case then according to 250.122(b) NEC 2017 you need to increase EGC. If you dont then why do it for new install as well because you didnt do it for existing ones and that are consider safe because they are existing

Where NEC specifies code language is correct new install and not for existing?

 

[wwhitney]

The rule states "When ungrounded conductors are INCREASED".

You can't stop reading there. It says (2017 NEC) "Where ungrounded conductors are increased in size from the minimum size that has sufficient
ampacity for the intended installation." So you compute the size I bolded, compare that to the size installed, and see if the installed size is larger. End of story.

Cheers, Wayne

 

[wwhitney]

Kind of wonder why we even have this rule.

The prototypical case is that you are running a long circuit and you increase the ungrounded conductor size to reduce voltage drop. The concern then is about voltage drop on the long EGC during a fault, and whether that could reduce the fault current enough to impeded OCPD operation. So the rule requires you to upsize the EGC correspondingly.

Which totally makes sense. However, crafting an easy to apply rule that covers that case and doesn't cover other cases like the OP that where it doesn't make sense has apparently been elusive.

Cheers, Wayne

 

[jap]

The language is ambiguous at best. A qualified person? I know we've discussed that definition before but it's becoming comical the way they've re-written 250.122(B) over and over again. And why no exception for a metal raceway that already qualifies as an EGC or do we
invoke the qualified person rule on that one too?

Pull the wire type EGC out and save money instead of spending it.

Jap>

You can't stop reading there. It says (2017 NEC) "Where ungrounded conductors are increased in size from the minimum size that has sufficient
ampacity for the intended installation." So you compute the size I bolded, compare that to the size installed, and see if the installed size is larger. End of story.

Cheers, Wayne

You have to physically do something to increase the size of a conductor or install it.

We're not messing with the conductors at all when simply changing a fuse.

JAP>