What is the voltage rating of the transformer bank used to feed the 42-Circuit Panelboard HB?

What is the voltage rating of the transformer bank used to feed the 42-Circuit Panelboard HB?

• A. 120/240 V
• B. 208/120 V
• C. 480/208 V
• D. 277/480 V

Answer: (D)

In large commercial distribution, a 42-circuit panelboard like HB is usually fed from a 480Y/277 V system. That means the service provides 480 V between any two hot legs, and 277 V from each hot leg to neutral. The transformer bank is there to supply that 277 V for lighting and other branch circuits, while the panelboard’s equipment is designed to withstand the 480 V line-to-line between conductors. This combination—277/480 V—is the standard rating for such a setup, making it the best choice for feeding a sizable panelboard. The other voltages correspond to different system configurations (residential 120/240 V, common 208/120 V office systems, or transformer arrangements not aligned with a 42-circuit HB panelboard in this context), so they aren’t the typical fit here.

In large commercial distribution, a 42-circuit panelboard like HB is usually fed from a 480Y/277 V system. That means the service provides 480 V between any two hot legs, and 277 V from each hot leg to neutral. The transformer bank is there to supply that 277 V for lighting and other branch circuits, while the panelboard’s equipment is designed to withstand the 480 V line-to-line between conductors. This combination—277/480 V—is the standard rating for such a setup, making it the best choice for feeding a sizable panelboard. The other voltages correspond to different system configurations (residential 120/240 V, common 208/120 V office systems, or transformer arrangements not aligned with a 42-circuit HB panelboard in this context), so they aren’t the typical fit here.