Conduit Resistance

[nhee2]

I am looking for data regarding the resistance (ohms/ft) of an aluminum conduit? I thought I remember seeing a link to a table in this forum previously but cannot locate it. Does anyone have a reference for this?

 

[Phil Corso]

Nhee... suggestion:

NEC, Chapter 9, Table 9 lists an impedance value for cable in PVC, Aluminum, and Steel conduit! Subtracting the PVC listed-value from the Al listed-value, will yield an approximate value for Al-conduit alone!

Regards, Phil Corso

 

[luckylerado]

Nhee... suggestion:

NEC, Chapter 9, Table 9 lists an impedance value for cable in PVC, Aluminum, and Steel conduit! Subtracting the PVC listed-value from the Al listed-value, will yield an approximate value for Al-conduit alone!

Regards, Phil Corso

OP is asking for resistance of the raceway. The difference in Ohms that you would calculate will represent the impedance imposed on the circuit conductors by the raceway due to inductive reactance. Good thinking though.

Resistance of the raceway would be dependent on the way it is coupled and the material it is made from. OP says aluminum.

Might be able to measure it with a caliper and figure it from K. :angel:

 

[don_resqcapt19]

While not directly giving you the resistance of the conduit, the Steel Tube Institute's GEMI software lets you do fault return path calculations for steel and aluminum conduit and compare the conduit fault return path to an EGC of the wire type.

 

[Phil Corso]

LuckyLerado, I disagree.

Those values presented in the NEC Table are calculated based on Geometrics! One can't just add self-inductances of the cable-group to the self-inductance of the conduit.

One must know the mutual-inductance, between the two. It is quit a laborious (oops) procedure, hence it's best to use the charts and tables specifically made available to aid the person faced with the task!

In my experience, I never accepted a low-resistance measurement between a phase-conductor, and some some circuitous (opps, again) EGC, as being adequate! Instead, I insisted on AC-current tests!

Regards, Phil Corso

 

[nhee2]

Thanks everyone.

don_resqcapt19 that is the link I remember seeing.