When electrical power is applied to the bus, which relays are energized?

When electrical power is applied to the bus, which relays are energized?

• A. PCC only
• B. PCC and TCC
• C. TCC only
• D. None

Answer: (B)

When the bus is energized, any relays fed from that control power source come alive. The PCC (Power Control Center) powers the control and monitoring circuits, and the TCC (Trip Control Circuit) provides the path for trip signals to the breakers. Since both circuits draw from the same bus power, they both receive voltage and become energized as soon as power is applied. If the bus loses power, these relays would drop out, which is why the presence of bus power is what energizes them. The other options would imply only one circuit gets power or none, which isn’t the case here because both PCC and TCC are tied to the bus power.

When the bus is energized, any relays fed from that control power source come alive. The PCC (Power Control Center) powers the control and monitoring circuits, and the TCC (Trip Control Circuit) provides the path for trip signals to the breakers. Since both circuits draw from the same bus power, they both receive voltage and become energized as soon as power is applied. If the bus loses power, these relays would drop out, which is why the presence of bus power is what energizes them. The other options would imply only one circuit gets power or none, which isn’t the case here because both PCC and TCC are tied to the bus power.