---
id: 2026-05-19T09:48:52-0400
title: 2026-05-19 09:48:52
tags: []
daily: "[[2026-05-19]]"
---
# 2026-05-19 09:48:52

## Wire Properties

### Resistance

NEC Chapter 9 Tables [[nfpa-70_ch09#Table 8 Conductor Properties|8]]
and [[nfpa-70_ch09#Table 9 Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz, 75°C (167°F) — Three Single Conductors in Conduit|9]]
provide resistance values for sizes and materials of wires,
stated in their notes to be based on calculations
found in [[nbs_1966_handbook-100]]
and [[nbs_1972_handbook-109]].

#### International Annealed Copper Standard

The same tables give conductor conductivity as a percent of
[International Annealed Copper Standard (IACS)](https://en.wikipedia.org/wiki/International_Annealed_Copper_Standard),
viz. 100% for copper and 61% for aluminum.

The definition of the IACS,
as originally published in [[nbs_1914_circular-031]] is

$$
100\%\ \rm{IACS} \equiv 0.15328~\text{ohm (meter, gram) at 20°C},
$$

alternately denoted in [[nbs_1966_handbook-100]] as

$$
0.15328~\text{ohm-gram/meter$^2$ at 20°C}.
$$

These definitions are for **mass resistivity**.

**Volume resistivity** can be derived
using the density of copper at the same temperature,

$$
8.89~\text{gram/cm$^3$ at 20°C},
$$

or

$$
0.32117~\text{lb/in.$^3$ at 20°C}.
$$

The derived value of volume resistivity given by [[nbs_1966_handbook-100]] is

$$
0.017241~\text{ohm-mm$^2$/meter at 20°C}.
$$

equal to 58 S/mm at 20°C.
