If a transformer is protected by a code letter on its nameplate and a FLA value, which pieces of information are used to size the overload protection?

• A. Only the voltage
• B. Only the horsepower
• C. FLA and code letter
• D. The manufacturer’s name

Answer: (C)

Sizing overload protection for a transformer relies on two pieces of information: the transformer's full-load current (FLA) and the code letter that indicates its thermal/inrush characteristics. The FLA tells you how much current the transformer will draw at its rated load, so the protective device must be chosen to carry that current without nuisance trips. The code letter on the nameplate specifies the time-current behavior for overload conditions, reflecting how the transformer handles startup inrush and its thermal response. By using both together, you select a protection device that can tolerate normal inrush and progressive heating, yet will trip if the current stays above safe levels.

Voltage, horsepower, and the manufacturer's name don’t determine the proper overload setting. Voltage doesn’t define load current by itself, horsepower is not the direct basis for protection sizing in this context, and the name of the manufacturer isn’t used to set the protection.