In a 277/480-volt, 3Ø, 4-wire utility transformer bank feeding a panelboard, which phase is circuit 40 connected to?

In a 277/480-volt, 3Ø, 4-wire utility transformer bank feeding a panelboard, which phase is circuit 40 connected to?

• A. AØ
• B. BØ
• C. CØ
• D. DØ

Answer: (B)

In a 277/480-V three‑phase four‑wire panel fed from a transformer bank, the panelboard is wired with three hot buses, one for each phase, plus a neutral. The spaces in the panel are typically organized so that each phase fills a block of spaces. For many standard panels with 40 circuits, the first block of spaces goes to the first hot phase, the second block to the second hot phase, and the third block to the third hot phase. Circuit numbers ascend by block, so circuit 40 sits in the second block and is carried by the middle hot leg. That means circuit 40 is connected to the middle phase (the phase commonly labeled B in panelboards). The neutral is shared, so the circuit would be a hot-to-neutral connection on that middle phase, i.e., BØ.

In a 277/480-V three‑phase four‑wire panel fed from a transformer bank, the panelboard is wired with three hot buses, one for each phase, plus a neutral. The spaces in the panel are typically organized so that each phase fills a block of spaces. For many standard panels with 40 circuits, the first block of spaces goes to the first hot phase, the second block to the second hot phase, and the third block to the third hot phase. Circuit numbers ascend by block, so circuit 40 sits in the second block and is carried by the middle hot leg. That means circuit 40 is connected to the middle phase (the phase commonly labeled B in panelboards). The neutral is shared, so the circuit would be a hot-to-neutral connection on that middle phase, i.e., BØ.