Journeyman Electrician Practice Exam

Which conductor insulation type has a higher temperature rating in a dry location compared to a wet location?

1. THHN

2. THWN

3. THHW

4. NM-B

The correct answer is: THHW

The conductor insulation type that has a higher temperature rating in a dry location compared to a wet location is indeed THHW. This designation stands for Thermoplastic Heat and Water-resistant, and it is designed to withstand higher temperatures and moisture. In dry environments, THHW conductors can typically operate at a maximum temperature of 90 degrees Celsius (194 degrees Fahrenheit). However, when used in wet locations, the maximum operating temperature drops to 75 degrees Celsius (167 degrees Fahrenheit). This characteristic makes THHW particularly versatile, as it provides excellent performance in conditions where moisture is not present. It is important for electricians to understand these ratings to ensure safety and compliance with electrical codes when selecting the appropriate wiring for different environments, thus ensuring optimal performance and minimizing the risk of overheating or failures. In contrast, other types of insulation such as THHN and THWN have specific ratings that are suitable for either dry or wet conditions, but do not offer the same high temperature rating in dry spaces as THHW does. NM-B, or Non-Metallic Sheathed Cable, is typically used for residential wiring and has limitations regarding temperature ratings compared to the options that are designed for higher heat resistance. Thus, THHW's design focusing on temperature resilience in dry conditions makes it the