mstrlucky74
Senior Member
- Location
- NJ
Anyone know of any situation where you would have (3) #350 with a #350 ground? The same size ground is the question.
Full Size G
- Thread starter mstrlucky74
- Start date
- Status
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Parallel install maybe. Each conduit needs an EGC based on the OCPD.
A 2500A breaker means a 350 kcmil EGC in each pipe.
A 2500A breaker means a 350 kcmil EGC in each pipe.
mstrlucky74
Senior Member
- Location
- NJ
But same size ground as phase conductors?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
As Derek stated in parallel conductors also in engineering mistakes or the absolute desire to waste someones money. I did see a spec once where they wanted the EGC two sizes larger than the circuit conductors for A/V receptacles in a Broadway Theater.
If you used many parallel sets it could actually be larger in each set.
If you used many parallel sets it could actually be larger in each set.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
I have pulled #10s for 20A (#12 circuit conductors) for A/V also.
Not my money, so I said “okay, no problem.”
mstrlucky74
Senior Member
- Location
- NJ
What does the parallel sets have to do with it? Is it because then you obviously have a larger load/amperage thus requiring the EGC to match the OCPD?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Read 250.122(F).
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Jumper gave you the code reference. The EGC in each parallel raceway is sized according to the OCPD ahead of the feeder. See post #2.
kwired
Electron manager
- Location
- NE Nebraska
Basically any time you increase conductor size for voltage drop reasons you need to proportionially increase the EGC size. If before increasing conductor size the EGC was same size as the ungrounded conductors then proportionally increasing the EGC will give you same size on both after the increase.
Example 30 amp circuit - 10 AWG ungrounded , 10 AWG EGC - typical for short run. Make that run long enough you decide to increase ungrounded conductors to 350 - EGC also needs increased to 350.
The parallel runs thing others mentioned has to do with EGC needing to be sized to OCPD. Often it is still smaller then the ungrounded conuctors, but the more parallel sets you run the smaller the individual ungrounded conductors can be - and very well could end up same or even smaller then the minimum required EGC at some point.
Example 30 amp circuit - 10 AWG ungrounded , 10 AWG EGC - typical for short run. Make that run long enough you decide to increase ungrounded conductors to 350 - EGC also needs increased to 350.
The parallel runs thing others mentioned has to do with EGC needing to be sized to OCPD. Often it is still smaller then the ungrounded conuctors, but the more parallel sets you run the smaller the individual ungrounded conductors can be - and very well could end up same or even smaller then the minimum required EGC at some point.
Yes, it can be just as large as the phase conductors, but I think there is a exception that says the ground doesn't have to be larger than the phase conductors.
On the original post, you are referring to a 3 phase, 3 wire load, right? You aren't talking about a service grounded conductor, are you?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
That exception would not apply for parallel.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
l meant for 250.122 , EGCs, and parallel.
Maybe you were thinking of T250.102 and note 1 perhaps?
My bad. That's exactly what I was thinking of.
mstrlucky74
Senior Member
- Location
- NJ
smoothops10
Member
- Location
- FL
- Occupation
- EE
250.122(A) states "but in no case shall be required to be larger than the circuit conductors supplying the equipment". This would include the case for conductors in parallel imo.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
True, but the circuit conductors are the total of all of the sets not just the size of the conductors in each raceway. In Jumpers example back in Post #2 for a 2500 amp OCPD you would have a 350 kcmil EGC in each parallel raceway.
If the circuit conductors were 10 sets of 250 kcmil (255 amps*10=2550 amps) the EGC in each raceway would still be 350 kcmil because the circuit conductors are actually 2500 kcmil (250 kcmil * 10 sets = 2500 kcmil).
smoothops10
Member
- Location
- FL
- Occupation
- EE
I see your point though and believe you are correct. Though I do think 10 sets of 350kcmil is an unlikely feeder vs 7 sets of 500 where it would be a non issue. There was a 2011 ROP that supports your comment.
5-287 Log #3816 NEC-P05 Final Action: Reject
(250.122(A))
_______________________________________________________________
Submitter: Christel K. Hunter, Alcan Cable
Recommendation: Add new text to read as follows:
250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum equipment
grounding conductors of the wire type shall not be smaller than shown in Table
250.122, but in no case shall they be required to be larger than the circuit
conductors supplying the equipment, including in parallel circuits. Where a
cable tray, a raceway, or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 250.118 and 250.134(A), it shall comply
with 250.4(A)(5) or (B)(4).
Substantiation: Until the reorganization of the Code in 1999, the EGCs in
parallel circuits were not required to be larger than the circuit conductors.
When 250.122 was reorganized, the exception that clarified this case was
moved into (A). Until recently, AHJs have agreed that the language in (A)
applies to (F), parallel circuits. However, there has been a change in
enforcement in the last few years after the publication of articles interpreting
this code language. Even with the addition of the language “in no case” in the
2008 NEC, there are still AHJs requiring that the EGCs be larger than the
ungrounded conductors in some parallel circuits.
The language proposed would clarify that the EGCs need not be larger than
the ungrounded conductors in parallel circuits. This was clearly the case until
the 1999 NEC, and no proposal was made nor substantiation provided to
change the application of the code. It appears that the intent of the changes
made at that time were simply to clean up the language and use positive
language. However, the editorial changes have resulted in an unintended
technical change that was never proposed nor discussed by the CMP.
Panel Meeting Action: Reject
Panel Statement: The substantiation provided does not support reducing the
current sizing requirement. The panel concludes that the rating of the
overcurrent device is the determining feature for sizing all equipment
grounding conductors, including those installed in parallel circuits.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 13 Negative: 3
Explanation of Negative:
DOBROWSKY, P.: Accepting this change would match the requirements for
supply side bonding jumpers installed in parallel.
MOHLA, D.: This propsal should have been either accepted or as a minimum
required a clear statement by the panel that that parallel circuits conductors are
also circuit conductors and included. The submitter is correct in stating the
requirement that “in no case the equipment grounding conductors are required
to be larger than the circuit conductors” apply also to parallel circuits.Identical
requirements exist in 250.24 (C) (1) for grounded conductor brought to Service
Equipment and in 250.30 (A) (8) (a) for grounded conductor for separately
derived systems. Grounded conductor on the supply side of overcurrent
protective device performs the same function as EGC on the load side of the
overcurrent protective device i.e. provides a path for ground fault currents.
Sizing requirements for supply side grounded conductors and load side EGC
should be same as they perform the same function during ground fault
conditions.
TEMBLADOR, R.: One primary factor that limits the current that flows
during a ground fault is the impedance of the circuit or circuits. Within a
specific circuit, the weakest link (highest impedance) in the chain of devices
connected together limits the current.
There are multiple circuit paths that are formed during a ground-fault
condition which are primarily comprised of the ungrounded circuit conductor,
equipment grounding conductors (EGC) and bonded metal enclosing the circuit
conductors. During a phase-to-ground fault in a circuit with paralleled
conductors, ground fault current will travel down all available paths to return to
the source. The current that flows divides at the point of the fault and travels
back to the source through both ends at which the ungrounded conductor, and
the bonded metal enclosing the circuit conductors or EGC’s are paralleled, or
both. Current flowing down the EGC’s and bonded metal enclosing circuit
conductors does not only flow down one path. It too will travel down all
available paths to return to the source. Consider a ground fault scenario where
the EGC’s are larger than the phase conductors. In this instance, the weakest
link in the circuit is the paralleled ungrounded phase conductor and it will limit
the fault current.
The equipment grounding conductors should not be required to be larger than
the ungrounded phase conductors where conductors are paralleled in multiple
raceways or cable.
5-287 Log #3816 NEC-P05 Final Action: Reject
(250.122(A))
_______________________________________________________________
Submitter: Christel K. Hunter, Alcan Cable
Recommendation: Add new text to read as follows:
250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum equipment
grounding conductors of the wire type shall not be smaller than shown in Table
250.122, but in no case shall they be required to be larger than the circuit
conductors supplying the equipment, including in parallel circuits. Where a
cable tray, a raceway, or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 250.118 and 250.134(A), it shall comply
with 250.4(A)(5) or (B)(4).
Substantiation: Until the reorganization of the Code in 1999, the EGCs in
parallel circuits were not required to be larger than the circuit conductors.
When 250.122 was reorganized, the exception that clarified this case was
moved into (A). Until recently, AHJs have agreed that the language in (A)
applies to (F), parallel circuits. However, there has been a change in
enforcement in the last few years after the publication of articles interpreting
this code language. Even with the addition of the language “in no case” in the
2008 NEC, there are still AHJs requiring that the EGCs be larger than the
ungrounded conductors in some parallel circuits.
The language proposed would clarify that the EGCs need not be larger than
the ungrounded conductors in parallel circuits. This was clearly the case until
the 1999 NEC, and no proposal was made nor substantiation provided to
change the application of the code. It appears that the intent of the changes
made at that time were simply to clean up the language and use positive
language. However, the editorial changes have resulted in an unintended
technical change that was never proposed nor discussed by the CMP.
Panel Meeting Action: Reject
Panel Statement: The substantiation provided does not support reducing the
current sizing requirement. The panel concludes that the rating of the
overcurrent device is the determining feature for sizing all equipment
grounding conductors, including those installed in parallel circuits.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 13 Negative: 3
Explanation of Negative:
DOBROWSKY, P.: Accepting this change would match the requirements for
supply side bonding jumpers installed in parallel.
MOHLA, D.: This propsal should have been either accepted or as a minimum
required a clear statement by the panel that that parallel circuits conductors are
also circuit conductors and included. The submitter is correct in stating the
requirement that “in no case the equipment grounding conductors are required
to be larger than the circuit conductors” apply also to parallel circuits.Identical
requirements exist in 250.24 (C) (1) for grounded conductor brought to Service
Equipment and in 250.30 (A) (8) (a) for grounded conductor for separately
derived systems. Grounded conductor on the supply side of overcurrent
protective device performs the same function as EGC on the load side of the
overcurrent protective device i.e. provides a path for ground fault currents.
Sizing requirements for supply side grounded conductors and load side EGC
should be same as they perform the same function during ground fault
conditions.
TEMBLADOR, R.: One primary factor that limits the current that flows
during a ground fault is the impedance of the circuit or circuits. Within a
specific circuit, the weakest link (highest impedance) in the chain of devices
connected together limits the current.
There are multiple circuit paths that are formed during a ground-fault
condition which are primarily comprised of the ungrounded circuit conductor,
equipment grounding conductors (EGC) and bonded metal enclosing the circuit
conductors. During a phase-to-ground fault in a circuit with paralleled
conductors, ground fault current will travel down all available paths to return to
the source. The current that flows divides at the point of the fault and travels
back to the source through both ends at which the ungrounded conductor, and
the bonded metal enclosing the circuit conductors or EGC’s are paralleled, or
both. Current flowing down the EGC’s and bonded metal enclosing circuit
conductors does not only flow down one path. It too will travel down all
available paths to return to the source. Consider a ground fault scenario where
the EGC’s are larger than the phase conductors. In this instance, the weakest
link in the circuit is the paralleled ungrounded phase conductor and it will limit
the fault current.
The equipment grounding conductors should not be required to be larger than
the ungrounded phase conductors where conductors are paralleled in multiple
raceways or cable.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
I thought they removed that sentence from 250.122. Still does not apply to parallel though.
smoothops10
Member
- Location
- FL
- Occupation
- EE
I still agree and the code says what is says but realistically there is no good reason engineering wise to have an unheated egc larger than the heated ccc's to clear a fault which is the reason the egc is there at all. Again, practically I only see this debate mattering for feeders above 4000A LV because noone is likely to be pulling multiple sets of 1/0 or whatever.
packersparky
Senior Member
- Location
- Wisconsin
- Occupation
- Inspector
In what installation would "but in no case shall they be required to be larger than the circuit conductors supplying the equipment." apply except for parallel conductors? Feeder taps might be one case, but that is already addressed in 250.122(G).
I can't think of any. If the CMP intended it to apply to the parallel sets of conductors they should have worded it like Note 1 to table 250.102(C).
I can't think of any. If the CMP intended it to apply to the parallel sets of conductors they should have worded it like Note 1 to table 250.102(C).
- Status