PVC Conduit Vs. Steel Conduit in regards to voltage drop

[Archery Coach]

I have recently just read in a text book that several organizations use, that" PVC Conduit reduces the amount of voltage drop compared to identical conductors in steel conduit". I have been in the trade for 20 years, and this is the first time that I have come across this, and am questioning it's validity. I have been taught that it is based on the resistance of the conductor itself, (2KxLxI/CM) not the raceway. My calculations have never taken into account the raceway, nor can I find a formula that takes into account the raceway. Before I send a letter to the publisher on the mistake, I wanted to make sure I haven't missed something over the last 20 years. Can anyone shed any light on the matter?

 

[Dennis Alwon]

I don't see where raceway fits into the formula for VD. It does come into play when calculating AIC - available fault current.

 

[Ingenieur]

I don't see where raceway fits into the formula for VD. It does come into play when calculating AIC - available fault current.

Table 9

effective Z increases for larger cables PVC vs steel (alum falls in the middle)

eg 3/0 Cu
PVC 0.088 ohm/1000'
Steel 0.094
7% increase

since V drop ~ Z it will increase with steel

for 12 awg
PVC 1.7
steel 1.7
no real difference

500 kcmil
PVC 0.048
Steel 0.057
20% increase

 

[dkidd]

The steel raceway increases the reactance of the wire run, which increases the voltage drop.

 

[Carultch]

I have recently just read in a text book that several organizations use, that" PVC Conduit reduces the amount of voltage drop compared to identical conductors in steel conduit". I have been in the trade for 20 years, and this is the first time that I have come across this, and am questioning it's validity. I have been taught that it is based on the resistance of the conductor itself, (2KxLxI/CM) not the raceway. My calculations have never taken into account the raceway, nor can I find a formula that takes into account the raceway. Before I send a letter to the publisher on the mistake, I wanted to make sure I haven't missed something over the last 20 years. Can anyone shed any light on the matter?

That formula is oversimplified, and is meant for the case when AC-specific factors are insignificant. Either due to being DC, or due to small conductors (generally smaller than 1/0).

The NEC has tables for AC resistance, where the kind of conduit does come in to play. PVC does not enhance the magnetism and inductive effects, while steel does.