extension from non grounding circuits.

[Riograndeelectric]

when making an extension from non grounding circuit in accordance with 250.130(C)(2) " any accessible point on the grounding electrode system as described in 250.50."
how does one determine a manner in which creates a low -impedance path?

how do you determine if an existing electrical system for the 1940s and 50s etc that were originally installed as non grounding circuits determine if the metal raceway A/C , EMT and Black ridgid pie are have a low impedance path and can be used to make an extension to new receptacles, lights etc?

250.118 types of equipment Grounding conductors.250.118(4) EMT
on page 244 of 2008 hand book FPN : for effective ground -Fault path, see 250.2 definition. in Reading Thur 250 I see 25.4(5) Effective ground fault current path.

 

[hurk27]

basically if you have a metal raceway, about the only one not allowed to be used for a fault current path is old BX, the rest could be checked with a low resistance ohm meter, one that will measure from 1 ohm and below. 250.130(C)(2) is one code that does allow a EGC to be ran separately from the circuit conductors when you run to the electrode system. at least thats my take on it.
I have never seen black ridge conduit, but I have seen where they used old gas pipe that used to feed gas lanterns, is this what you thinking of?, I had one house where the whole house was wired like this through the old gas pipes and even through the old Elbows how they got them through then I have no idea. remember the water pipe after the first 5' into the building is no longer part of the electrode system so it cant be used.

 

[Riograndeelectric]

and you would verify that you have low restive Reading and if so then you would go ahead and use the pipe, EMT and but not the old BX cable.
I thought that the fittings and boxes had to be listed for use a grounding?

 

[hurk27]

and you would verify that you have low restive Reading and if so then you would go ahead and use the pipe, EMT and but not the old BX cable.
I thought that the fittings and boxes had to be listed for use a grounding?

BX is not listed in 250.118 as a grounding pathway for one reason, there in no shunt conductor inside to shunt the spirals of the outer jacket, which is why type AC can be used, MC has a grounding conductor, if you read 250.118 you will find the only requirements for listed fittings for grounding are for flexible metal conduits, not for non flexible methods.

 

[Riograndeelectric]

Thanks for your input. I think the NEC needs to come up with better reasoning of low impedance.. excellent suggestion on verifying restiance to ground on the existing EMT.
one never knows for sure if the ground is in fact a true ground and not the conduit in contact with other metal piping, framing lath etc