Grounding Electrode Conductor with Branch Circuits

Status
Not open for further replies.
N

NTesla76

Senior Member
Location
IA
Occupation
Electrics
I've looked over 250.64 and I can't see where it states the grounding electrode conductor cannot be installed with branch circuits. Is this one of those trade standards but no code requirement. Curiosity got me.
 
lauraj said:
You would just need to bond the raceway as required in 250.64(E).
Click to expand...
Correct, if you're using the raceway as protection of the GEC. But I can't find anywhere stating the GEC can't be installed with branch circuits.
 
There is a bit of a myth going around that GEC cannot be in a BC conduit. I think this comes from the prohibition on unprotected service conductors being there. But a GEC is not a service conductor.
 
lauraj said:
You would just need to bond the raceway as required in 250.64(E).
Click to expand...
I know this question will look stupid. But I would like to know the reasoning to have to bond it to the raceway. Not that I doubt it or think anything like that, I just honestly wanna know the theory behind it.
 
Dsg319 said:
I know this question will look stupid. But I would like to know the reasoning to have to bond it to the raceway. Not that I doubt it or think anything like that, I just honestly wanna know the theory behind it.
Click to expand...
The concern is the choke (inductive) effect of the conduit during extreme lightning-induced currents raising the impedance of the GEC and reducing its conductivity and effectiveness. Bonding at both ends minimizes this effect by using the conductor to "short out" the inductor.


How was that?
 
LarryFine said:
The concern is the choke effect of the conduit during extreme lightning-induced currents raising the impedance of the GEC and reducing its conductivity and effectiveness.


How was that?
Click to expand...
That wasn’t bad! Thank you I appreciate it. So one could say in laymen’s terms it can hender the effectiveness of the GEC of not properly bonded to the raceway it installed in.
 
LarryFine said:
The concern is the choke (inductive) effect of the conduit during extreme lightning-induced currents raising the impedance of the GEC and reducing its conductivity and effectiveness. Bonding at both ends minimizes this effect by using the conductor to "short out" the inductor.


How was that?
Click to expand...
How effective is it anyway?
 
Correctamundo. Not so different from the reason for the bonding strip added to BX and AC cables.


Note: I added to my response above after posting it, which is why the quotes differ.
 
petersonra said:
The bonding strip in those cables is there because the armor is not an effective EGC without it.
Click to expand...
Right, because of inductance caused by the spiral construction. The bonding strip is not there to act as an end-to-end EGC, but rather to effectively short out adjacent turns of the spiral, so it acts more as a straight tube during faults.
 
petersonra said:
I meant the idea that somehow bonding the GEC to the conduit makes any real difference in how it works if lightning strikes?
Click to expand...
I imagine that this, like most code rules, evolved from observation of what happened before it was implemented.
 
tom baker said:
Absolutely it
Click to expand...
I stated on my cell phone and sometimes I don't hit save...
So my complete answer is
Absolutely bonding the raceway makes a difference. If not bonded at each end, only 3% of the fault current will be conducted. The concern with lightning is the impedance due to high frequency and large current, which at 60 hz are not a concern. Bonding to the metallic raceway greatly increased the surface area and lowers the impedance. My information comes from the IEEE Green (grounding) Book if you want to look at the source. I suspect this bonding (and ground rods) was all worked out in the early 1920s.
 
Status
Not open for further replies.
Top