What does HH indicate in wire classification?

• A. Highly heat-resistant wire, resistant up to 194°F
• B. High-humidity rating
• C. Heavy gauge
• D. Hardened insulation

Answer: (A)

Understanding wire insulation labels helps you pick the right wire for heat conditions. HH is a high-heat insulation rating, meaning the insulation can handle elevated temperatures up to about 194°F (90°C). This matters because in environments with more heat, using wire with this higher rating reduces the risk of insulation damage and electrical fires.

It’s not about humidity, gauge, or making the insulation harder. A humidity rating would involve moisture resistance specifics, which are not conveyed by this code. Gauge relates to the conductor size and how much current it can carry, not the insulation’s temperature tolerance. Hardened or stiffened insulation isn’t a standard rating conveyed by HH. In modern wiring, you’ll often see explicit temperature ratings (like 75°C or 90°C) on wires, but HH indicates that higher-heat capability was recognized in the insulation.