The smallest THHN/THWN copper grounded conductor that can be installed for a service is ___ when the ungrounded conductors are 1/0 THWN/THHN copper.

The smallest THHN/THWN copper grounded conductor that can be installed for a service is ___ when the ungrounded conductors are 1/0 THWN/THHN copper.

• A. 6
• B. 2
• C. 3
• D. 1/0

Answer: (A)

Sizing the grounded conductor (the neutral) in a service is driven by the service’s overcurrent protection. When the ungrounded conductors are 1/0 copper, you’re dealing with a fairly large service, typically around 150 A. For that level of protection, the neutral must be at least a certain minimum size, which in this scenario is 6 AWG copper. So the smallest grounded conductor you can install for this service is 6 AWG. The other options listed (2, 3, or 1/0) are larger conductors and would be acceptable, but they aren’t the smallest size that meets the requirement.

Sizing the grounded conductor (the neutral) in a service is driven by the service’s overcurrent protection. When the ungrounded conductors are 1/0 copper, you’re dealing with a fairly large service, typically around 150 A. For that level of protection, the neutral must be at least a certain minimum size, which in this scenario is 6 AWG copper. So the smallest grounded conductor you can install for this service is 6 AWG. The other options listed (2, 3, or 1/0) are larger conductors and would be acceptable, but they aren’t the smallest size that meets the requirement.