Fortunat Mueller
Member
- Location
- Portland, ME
Hi all,
This is my first posting to this forum, so please be gentle.
I'm trying to reconcile two different interpretations of 250.166(c) and am hoping someone here can weigh in. Specifically, I am trying to understand what is meant by : "that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger..." ?
I have gnereally read that to mean that a GEC running to a ground rod doesn't have to be larger than 6 AWG in any case (I assume that is because the contact resistance with the ground is naturally going to limit the fault current to a level where 6 is ample in size). But what is meant by 'the sole' connection in that section? If there is more than one wire landing on ground rod (i.e. the DC/AC bonding jumper) does it no longer apply?
For example, in a grid tied system if we're driving a new, dedicated DC Grounding Electrode according to 690.47(C) (1) and then bonding it to the existing AC electrode as required, can we still size the GEC according to 250.166(c)? Or is the GEC now no longer the 'sole connection' to the electrode and thus we need to size according to 250.166(A) or (B)?
That seems to be the interpretation in Mike Holts' book where his note says that (C) and (d) only apply in stand alone DC systems. But other interpretations (including, I think, John Wiles) differ and say basically that as long as your just connecting to ground rods (not building steel etc) the sizing of the GEC can be done according to 250.166(C) (and then the DC/AC bonding jumper gets sized at the larger of the AC or DC GEC).
Anyone have an opinion about that?
Thanks
~Fortunat
This is my first posting to this forum, so please be gentle.
I'm trying to reconcile two different interpretations of 250.166(c) and am hoping someone here can weigh in. Specifically, I am trying to understand what is meant by : "that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger..." ?
I have gnereally read that to mean that a GEC running to a ground rod doesn't have to be larger than 6 AWG in any case (I assume that is because the contact resistance with the ground is naturally going to limit the fault current to a level where 6 is ample in size). But what is meant by 'the sole' connection in that section? If there is more than one wire landing on ground rod (i.e. the DC/AC bonding jumper) does it no longer apply?
For example, in a grid tied system if we're driving a new, dedicated DC Grounding Electrode according to 690.47(C) (1) and then bonding it to the existing AC electrode as required, can we still size the GEC according to 250.166(c)? Or is the GEC now no longer the 'sole connection' to the electrode and thus we need to size according to 250.166(A) or (B)?
That seems to be the interpretation in Mike Holts' book where his note says that (C) and (d) only apply in stand alone DC systems. But other interpretations (including, I think, John Wiles) differ and say basically that as long as your just connecting to ground rods (not building steel etc) the sizing of the GEC can be done according to 250.166(C) (and then the DC/AC bonding jumper gets sized at the larger of the AC or DC GEC).
Anyone have an opinion about that?
Thanks
~Fortunat