If exposed structural metal that is interconnected to form the building frame exists in the area served by the separately derived system, it shall be bonded to the grounded conductor of each separately derived system and each bonding jumper shall be sized in accordance with Table 250.102(C)(1) based on the largest ungrounded conductor of the service.

• A. True
• B. False
• C. Not specified
• D. Depends

Answer: (B)

The test is about bonding exposed structural metal when a separately derived system serves the area. When a building region is fed by a separately derived system (such as a transformer that provides its own grounded conductor), the exposed structural metal within that area must be bonded to the grounded conductor of that separately derived system. This creates a continuous, low-impedance path for fault current and helps keep all metal parts at the same potential, improving safety. If more than one separately derived system serves the area, you bond to the grounded conductor of each of those systems.

The size of the bonding jumper is determined using Table 250.102(C)(1) and is based on the largest ungrounded conductor of the system being bonded—the separately derived system—not the largest ungrounded conductor of the service. So the statement is not correct because it references the service conductor size rather than the size of the separately derived system being bonded.