Coated vs. Uncoated Copper Wires

Grouch

Grouch

Senior Member
Location
New York, NY
Table 8 in Chapter 9 includes columns for coated and uncoated copper wires, under DC resistance.
Table 9 in Chapter 9 only includes a column for uncoated copper wires, under AC resistance.

How come Table 9 doesn't include information for coated copper wires?
 
A standard presents certain values in certain conditions-usually close to general situations. If the installation conditions are far from the standard you may use "Engineering Supervision"- that means to calculate the impedance of the cable or wire in different conditions. You may use it in order to calculate ampacity or voltage drop or short-circuit currents.
In NEC World you may consult Annex B, or Neher and McGrath Publication or IEEE 835/1994, usually.
In my opinion, you better consult the IEC World standards as IEC 60287-1-1 and IEC 60228.
The wire impedance presents two components: reactance and resistance.
The reactance does not depend on resistance, so for coated copper will be more or less the same [the diameter difference has a little influence here].However, the conductor diameters, the geometric position of different bunch of wire, dimensions of conduits or another raceway are important.
The resistance is connected to temperature, skin effect, proximity effect, metallic conduit influence and other.
If your cables run in cable tray- except NEC art 392-you may consult
ANSI-NEMA WC51Ampacities-in-Cable-Trays [ICEA P-54-440].
However, since the are many approximations as weight and diameter tolerances an up to 5% from minimum to maximum value are always.
So, in my humble opinion, NEC Tables [updated edition] are enough accurate.
 
At power line frequencies, reasonable length wires have the same resistance and impedance. True the power company may have a different view-point for miles long wires. But at lightning frequencies, it's a very different story.
 
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