Grounding vs. Grounded

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Hameedulla-Ekhlas

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AFG
:D

I agree the requirements in 250.4(A)(5) and (B)(4) are vague and possible unenforceable.

Chris
how you can say vague there is nothgin vague in NEC. Please read the below for reason.

In NEC-250.4(A)(5), we find a definition of an effective ground fault current path

" An intentionally constructed, permanent, low impedance electrically conductive path designed and intended from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protection device or ground fault detectors on high impedance grounded system"

Under fault current condition, the possible burning off of an equipment grounding conductor, a bonding jumper, or any conductor that is dependent upon safely carrying fault current until the overcurrent protective device can clear the fault result in a hazard to life, safety and equip,ent.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Okay, I will bite. When? I ask only to learn.
Well I had to think because the original thought I had was wrong. I was thinking if the egc had to be upsized based on art. 250.122(B), then the grounding conductor would have to be larger than the grounded conductor. I don't think this is correct because the neutral would have to bve at least the same size as the grounding conductor in order to safely clear ground fault.

Specifically I was thinking of a feeder to a panel where the neutral load was minimum (10 amps or so) but the feeders OCPD where a 100 amp.

I now realize that the neutral cannot be smaller than the grounding but could be the same time.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
how you can say vague there is nothgin vague in NEC. Please read the below for reason.

In NEC-250.4(A)(5), we find a definition of an effective ground fault current path

" An intentionally constructed, permanent, low impedance electrically conductive path designed and intended from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protection device or ground fault detectors on high impedance grounded system"

Under fault current condition, the possible burning off of an equipment grounding conductor, a bonding jumper, or any conductor that is dependent upon safely carrying fault current until the overcurrent protective device can clear the fault result in a hazard to life, safety and equip,ent.
Here is what I meant by vague, (And there are many things in the NEC that are vague:D)

The definition that you posted does not contain any prescriptive measures as to what is considered an "Effective ground fault current path".

What would be considered to be low impedance?

Chris
 

jumper

Senior Member
Well I had to think because the original thought I had was wrong. I was thinking if the egc had to be upsized based on art. 250.122(B), then the grounding conductor would have to be larger than the grounded conductor. I don't think this is correct because the neutral would have to bve at least the same size as the grounding conductor in order to safely clear ground fault.

Specifically I was thinking of a feeder to a panel where the neutral load was minimum (10 amps or so) but the feeders OCPD where a 100 amp.

I now realize that the neutral cannot be smaller than the grounding but could be the same size.
This I understand. Thanks.
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Hameedulla-Ekhlas, thinking we have different sized code books...my Table 250.122 is on page 117. To keep clarity in mind, if we define it by Article and section number, it won't matter what page it is on, we will both be on the same page for gleaning the information.

And am in the boat that the grounded or grounding conductors will not be larger than any of the current carrying conductors that are protected by an ocpd.
I dont have any different book with me. It is a NEC-2008 blue cover with three names
Mark W.Early
Jeffrey S.Sargent
Joseph V.Sheehan
E. William Buss
Eleventh Edition

Exactly page-249
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Can you point out the NEC section that specifies exactly what an effective ground fault current path is? :)

Just how fast does the OCPD have to operate?

Just saying ..... :)
Fast enough to "prevent extensive damage to the electrical components of the circuit".
 

buffnitup

Member
Here is what I meant by vague, (And there are many things in the NEC that are vague:D)

The definition that you posted does not contain any prescriptive measures as to what is considered an "Effective ground fault current path".

What would be considered to be low impedance?

Chris
Not to disrupt this forum. Maybe low is 25 Ohms when referring to electrode resistance in article 250? Dunno. Just a thought?
 
I dont have any different book with me. It is a NEC-2008 blue cover with three names
Mark W.Early
Jeffrey S.Sargent
Joseph V.Sheehan
E. William Buss
Eleventh Edition

Exactly page-249


I figured it out:)... You are using the Neational Electrical Code Handbook. Have to be careful that what you quote out of there is actual NEC verbiage, not the commentary by some sharp people that help intrepret the code. Currently have a black and red, 2008 NEC code book that I won at a drawing at IAEI seminar last year. Actually it's the second one I have for 2008...who's counting? Believe a I got it from the Chief Moderator here as a matter of fact!
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Here is what I meant by vague, (And there are many things in the NEC that are vague:D)

The definition that you posted does not contain any prescriptive measures as to what is considered an "Effective ground fault current path".

What would be considered to be low impedance?

Chris
it should be commented in next version of NEC this note whether to be removed or cleared.
 

cmccabe

Member
Well I had to think because the original thought I had was wrong. I was thinking if the egc had to be upsized based on art. 250.122(B), then the grounding conductor would have to be larger than the grounded conductor. I don't think this is correct because the neutral would have to bve at least the same size as the grounding conductor in order to safely clear ground fault.

Specifically I was thinking of a feeder to a panel where the neutral load was minimum (10 amps or so) but the feeders OCPD where a 100 amp.

I now realize that the neutral cannot be smaller than the grounding but could be the same time.
so the questions still stands where in the nec does it say my neutral cant be bigger then my grounding
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
so the questions still stands where in the nec does it say my neutral cant be bigger then my grounding
That has been answered numerous times already. The nec does not say that and in most cases the neutral is larger than the grounding (EGC) conductor
 

cmccabe

Member
so im safe to say the only rule that would apply would be that my grouding just couldnt be bigger then my conductors 250.122(A)
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
so im safe to say the only rule that would apply would be that my grouding just couldnt be bigger then my conductors 250.122(A)
Almost. The grounding conductor can be larger than the ungrounded conductors but there is no need to do that and a waste of wire.
 
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