What is the minimum size of the ungrounded conductors in each conduit feeding Panel A?

What is the minimum size of the ungrounded conductors in each conduit feeding Panel A?

• A. 3/0
• B. 2/0
• C. 4
• D. 4/0

Answer: (A)

Sizing the hot conductors for a feeder is all about making sure they can carry the full feeder current without overheating, given the overcurrent protection protecting Panel A. In this setup, the feeder to Panel A is protected at a certain ampere rating (the feeder’s OCP rating). The conductors must have an ampacity at least equal to that rating. For copper conductors run in conduit with insulation rated for the 75°C column (common for THHN in conduit), the smallest size that can meet a 200 A feeder is 3/0 AWG. That means 3/0 is the minimum required to safely carry the feeder current. A smaller size would be undersized and not permitted by the ampacity tables, while larger sizes would work but aren’t the minimum.

Sizing the hot conductors for a feeder is all about making sure they can carry the full feeder current without overheating, given the overcurrent protection protecting Panel A. In this setup, the feeder to Panel A is protected at a certain ampere rating (the feeder’s OCP rating). The conductors must have an ampacity at least equal to that rating.

For copper conductors run in conduit with insulation rated for the 75°C column (common for THHN in conduit), the smallest size that can meet a 200 A feeder is 3/0 AWG. That means 3/0 is the minimum required to safely carry the feeder current. A smaller size would be undersized and not permitted by the ampacity tables, while larger sizes would work but aren’t the minimum.