Section 5.2 of ICEA S-81-570 specifies that insulation tensile strength, elongation at rupture, and retention after air oven aging shall be tested per ANSI/NEMA WC-53 and meet Table 3-2 requirements.
For 75°C rated: initial 2000 psi min tensile, 300% min elongation; after aging 48h at 100°C, 75% retention. For 90°C rated: initial 1800 psi, 250% elongation; after aging 168h at 121°C, 75% retention.
Section 5 of ASTM B344 covers the physical requirements for nickel-chromium and nickel-chromium-iron alloy wire for electrical heating elements. The material must be thoroughly and uniformly annealed.
Wire of size 0.0035 inch (No. 39 AWG) and larger must meet a minimum elongation of 20% in a 10-inch gauge length. Wire from 0.0031 inch to 0.002 inch (Nos. 40 to 44 AWG) must meet 10% minimum elongation.
These elongation requirements ensure the heating element wire has adequate ductility for coiling and forming during manufacture of heating elements.