In the example of tap conductor calculations, what temperature rating is assumed for conductors and terminations?

• A. 60°C
• B. 75°C
• C. 90°C
• D. 105°C

Answer: (B)

Tap conductor calculations rely on the temperature rating of both the conductor insulation and its terminations because that rating determines how much current the wiring can safely carry. In many practical examples, the standard assumption is a 75°C rating for both conductors and terminations. This reflects modern wiring practices, where common insulation types (like THHN/THWN-2) and most terminations are rated at 75°C or higher, giving a higher, yet appropriate, ampacity for the conductors.

Using a 75°C rating keeps the calculation aligned with typical installations and avoids unnecessarily restricting the conductor size. If you were to assume a 60°C rating, you’d under-estimate the allowable current, which isn’t how these examples are usually modeled. Higher ratings like 90°C or 105°C are possible only when every termination along the path is guaranteed to be rated that high; otherwise the calculation must fall back to the lowest rating among the conductors and terminations involved.