Grounding Conductor

[retirede]

so how would we then deal with this kwired>>>>?

250.4A(5) Effective Ground-Fault Current Path. Electrical equip‐
ment and wiring and other electrically conductive material
likely to become energized shall be installed in a manner that
creates a low-impedance circuit facilitating the operation of the
overcurrent device or ground detector for high-impedance
grounded systems. It shall be capable of safely carrying the
maximum ground-fault current likely to be imposed on it from
any point on the wiring system where a ground fault may occur
to the electrical supply source. The earth shall not be consid‐
ered as an effective ground-fault current path

~RJ~

Is “safely carrying” defined in the NEC? If not, I’d contend that if the breaker trips with the “ground fault current path” (be it wire or raceway) still intact, the fault current was safely carried.

 

[LarryFine]

Installing a wire nut correctly is much more difficult than tightening a setscrew or locknut. Think about a bundle of say 5 wires with a mix of solid and stranded. ITs really not a trivial task. Being experienced, we often forget how difficult it is. Watch a newby try it and you wil probably think differently.

I agree with you on this. Wire (normally) doesn't go bad between boxes, but within them.

My son watches how carefully I make electrical connections, and he understands why.

I'm perfectly happy to install a wire EGC in conduit as long as someone is paying me to.

 

[romex jockey]

Is “safely carrying” defined in the NEC? If not, I’d contend that if the breaker trips with the “ground fault current path” (be it wire or raceway) still intact, the fault current was safely carried.

The ‘point’ is there exists no means within our code book to define this for a pipe run

Consider that T250.122, 392.60(B) , 12 ½%, T9Chap9, all either dictate sizing, or provide a means of calculation

~RJ~

 

[kwired]

The ‘point’ is there exists no means within our code book to define this for a pipe run

Consider that T250.122, 392.60(B) , 12 ½%, T9Chap9, all either dictate sizing, or provide a means of calculation

~RJ~

Does there need to be since 250.118 tells us the types of EGC's permitted? Makes sense they would tell what size wire type conductor to use, but raceways already somewhat sized according to what can be pulled in them. Maybe they have determined metal raceways will be sufficient enough to handle whatever the largest conductor that can be pulled in will be able to deliver. Keep in mind if you increase conductor size the raceway that it it installed in may also need increased.

Take a 3/4 raceway - you ever needed larger than a 8 AWG EGC in it? If in a situation where you did need larger EGC chances are your ungrounded conductors also are large enough you will be increasing raceway size. Also keep in mind the EGC never needs to be larger than the ungrounded conductors regardless of what size the ungrounded conductors are.

 

[romex jockey]

Does there need to be since 250.118 tells us the types of EGC's permitted?

last sentence in 250.118 Kwired>>>

(13) Other listed electrically continuous metal raceways and
listed auxiliary gutters


If it's 'listed', that means it's 'tested'

If it's 'tested', then it's 'rated'

If it's rated as an EGC, ohmic values apply

The steel institutes GEMI software portrays this

Our NEC does not

~RJ~

 

[kwired]

last sentence in 250.118 Kwired>>>

(13) Other listed electrically continuous metal raceways and
listed auxiliary gutters


If it's 'listed', that means it's 'tested'

If it's 'tested', then it's 'rated'

If it's rated as an EGC, ohmic values apply

The steel institutes GEMI software portrays this

Our NEC does not

~RJ~

All I can say is as long as metal raceways have been permitted with no other regard to selecting size the code making panel must have at some point determined it is not necessary to calculate this for most applications.

You are welcome to submit a PI for next code, they should give a reason why if it is rejected.

 

[romex jockey]

All I can say is as long as metal raceways have been permitted with no other regard to selecting size the code making panel must have at some point determined it is not necessary to calculate this for most applications.

You are welcome to submit a PI for next code, they should give a reason why if it is rejected.

thx....
This we've always done it that way mentality takes a backseat to new codes every cycle kwired

~RJ~

 

[kwired]

thx....
This we've always done it that way mentality takes a backseat to new codes every cycle kwired

~RJ~

We have always done it that way, but I have no idea if or how it may have been determined to be sufficient as is. Would likely been before any of us were born if it was determined to be sufficient as is. I don't know if anyone has submitted PI's/proposals in the past to change it either. Does seem very possible that it has been determined to be fine as it is at some point though.

If anything I could see RMC/IMC having higher values than EMT, but as is any metal raceway is acceptable except for flexible raceways that have other issues that go with them and do have specifically mentioned limitations.

 

[ggunn]

"Objection, your Honor! The witness is answering the question I asked."

"Incompetent, irrelevant, and immaterial!" - Perry Mason

 

[romex jockey]

Does seem very possible that it has been determined to be fine as it is at some point though.

The steel institutes GEMI software has done just that kwired.

the results of viability diminish as distance increases , simple ohms law

this is the manufacturer of the product

~RJ~

 

[kwired]

The steel institutes GEMI software has done just that kwired.

the results of viability diminish as distance increases , simple ohms law

this is the manufacturer of the product

~RJ~

So what is it again that you have been concerned about then?

Same thing happens with distance and a copper wire EGC.

We do have rule that if you increase ungrounded you need to increase grounding by a similar proportion, but there is still resistance in long runs on both grounding and ungrounded conductors. Seen many times where time to trip OCPD may not be all that instantaneous like it is on shorter runs even though installation is code compliant.

 

[ggunn]

So what is it again that you have been concerned about then?

Same thing happens with distance and a copper wire EGC.

We do have rule that if you increase ungrounded you need to increase grounding by a similar proportion, but there is still resistance in long runs on both grounding and ungrounded conductors. Seen many times where time to trip OCPD may not be all that instantaneous like it is on shorter runs even though installation is code compliant.

Didn't that rule go away in the 2020 NEC?

 

[wwhitney]

Didn't that rule go away in the 2020 NEC?

Well,, it's still there, but the language has been tweaked and an exception has been added:

(2020) 250.122(B) Increased in Size. If ungrounded conductors are increased in size for any reason other than as required in 310.15(B) or 310.15(C), wire-type equipment grounding conductors, if installed, shall be increased in size proportionately to the increase in circular mil area of the ungrounded
conductors.
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).

Now the question is how broadly the exception may be used and what procedure if any is required for a qualified person to decide the EGC doesn't need upsizing. Is it enough to say "hey, I upsized these ungrounded conductors for reason X, it would be NEC-compliant even if I didn't upsize the ungrounded conductors, and the normal size EGC would be an effective ground fault current path in that scenario, so I don't need to upsize my EGC"?

Cheers, Wayne

 

[kwired]

Well,, it's still there, but the language has been tweaked and an exception has been added:

(2020) 250.122(B) Increased in Size. If ungrounded conductors are increased in size for any reason other than as required in 310.15(B) or 310.15(C), wire-type equipment grounding conductors, if installed, shall be increased in size proportionately to the increase in circular mil area of the ungrounded
conductors.
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).

Now the question is how broadly the exception may be used and what procedure if any is required for a qualified person to decide the EGC doesn't need upsizing. Is it enough to say "hey, I upsized these ungrounded conductors for reason X, it would be NEC-compliant even if I didn't upsize the ungrounded conductors, and the normal size EGC would be an effective ground fault current path in that scenario, so I don't need to upsize my EGC"?

Cheers, Wayne

Wasn't aware of this change. Yes looks like you probably need to prove your chosen conductor is suitable to an AHJ if wanting to use the exception. I see they basically eliminated needing to do so for conductors increased in size for ambient temp or number of conductors in raceway adjustment reasons. Don't know if I totally agree with that, can still potentially result in similar situations as voltage drop reasons I would think.

Long run - increase conductor from 12 to 10 because of voltage drop - makes some sense as a general rule with no calculating necessary, but same run with more than 9 CCC's you are kind of forced to increase to 10 but that automatically takes care of voltage drop. EGC is carrying same fault current either way if remaining conditions are all the same.