Equipment Grounding

newt

Senior Member
I work for a Utility and we hooked up a 1200 amp service today. From the 1200 amp disconnect they ran a #6 equipment ground to the main sub panel. The inspector allowed this because the #6 wasn't needed as it was run in EMT. Another install involved a feeder tap from a 400 amp bus to a 200 amp disconnect. The equipment ground was a #6 that was too small for this install. The inspector said it ok because it run in EMT conduit. Is there anywhere in the code that states if a redundant ground is run, it must be appropriate size? Thanks in advance.
 

augie47

Moderator
Staff member
Location
Tennessee
AFIK, IF a conductor type equipment ground is installed in a raceway which qualifies as an equipment ground, the conductor must still be sized by the appropriate Table (250.122)
 

newt

Senior Member
AFIK, IF a conductor type equipment ground is installed in a raceway which qualifies as an equipment ground, the conductor must still be sized by the appropriate Table (250.122)
Thank you. Just what I thought. Some inspectors don't like to be proven wrong. Any advise on how to handle inspectors with an attitude that don't care to hear that they are mistaken??
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
There are a number of code users that say the same as the inspector in this case. I don't think the code clearly addresses the issue and I can see good arguments for either side.
 

Carultch

Senior Member
Location
Massachusetts
Yes, it makes it code compliant, but the impedance of the fault clearing path will be greater than it was with the non-compliant installation.
The reason it probably isn't compliant in the original situation is that the incorrect EGC cannot carry the fault current on its own. I would imagine that the intent of the rule is to have all possible EGC paths be independently compliant, and therefore not depending on any parallel EGC path.


Current doesn't just take the "path of least resistance". It takes all paths, of all resistances, inversely proportional to the resistance of each path.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
The reason it probably isn't compliant in the original situation is that the incorrect EGC cannot carry the fault current on its own. I would imagine that the intent of the rule is to have all possible EGC paths be independently compliant, and therefore not depending on any parallel EGC path.


Current doesn't just take the "path of least resistance". It takes all paths, of all resistances, inversely proportional to the resistance of each path.
I am not convinced that it is not compliant, but even if it is, disconnecting the EGC of the wire type, even where it is smaller than required by T 250.122, increases the impedance of the fault return path.

We are not "depending" in a parallel path here...the raceway is a compliant fault clearing path. There is a possibly non-compliant path connected in parallel. If the system is safe when you disconnect and tape up the EGC of the wire type, it is still safe if that conductor remains connected.
 
AFIK, IF a conductor type equipment ground is installed in a raceway which qualifies as an equipment ground, the conductor must still be sized by the appropriate Table (250.122)
The reason this installation should not be code compliant, even thought the total grounding path impedance is smaller than the EMT itself, is that with the GEC installed in the raceway, the raceway does not need to be compliant with the current capacity for fault clearing requirement. E.g. once GEC had been installed EMT can be substituted by flex metal conduit down stream, which by itself cannot be longer than 6 ft without GEC.
 

iwire

Moderator
Staff member
Location
Massachusetts
The reason this installation should not be code compliant, even thought the total grounding path impedance is smaller than the EMT itself, is that with the GEC installed in the raceway, the raceway does not need to be compliant with the current capacity for fault clearing requirement. E.g. once GEC had been installed EMT can be substituted by flex metal conduit down stream, which by itself cannot be longer than 6 ft without GEC.
This thread is not about a GEC.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
The reason this installation should not be code compliant, even thought the total grounding path impedance is smaller than the EMT itself, is that with the GEC installed in the raceway, the raceway does not need to be compliant with the current capacity for fault clearing requirement. E.g. once GEC had been installed EMT can be substituted by flex metal conduit down stream, which by itself cannot be longer than 6 ft without GEC.
What code section says that?
 

kwired

Electron manager
Location
NE Nebraska
The reason it probably isn't compliant in the original situation is that the incorrect EGC cannot carry the fault current on its own. I would imagine that the intent of the rule is to have all possible EGC paths be independently compliant, and therefore not depending on any parallel EGC path.


Current doesn't just take the "path of least resistance". It takes all paths, of all resistances, inversely proportional to the resistance of each path.
I'm pretty certain flexible conduits are not permitted to be used as an EGC on a 1200 amp circuit, but I may be off just a little here.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
NEC does not allow 6' or longer flexible metal conduit to serve as EGC unless a proper ground conductor is added. This means in this case the code allows the raceway does not need to be compliant with the current capacity for fault clearing requirement
Not exactly, because in that case a bonding jumper is required for the flexible conduit.
 
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