Which transformer size is indicated for a 24-amp panel requirement?

• A. A 20 amp transformer
• B. A 40 amp transformer
• C. A 50 amp transformer
• D. A 30 amp transformer

Answer: (B)

Sizing a transformer for an alarm panel means providing enough current to meet the panel’s demand with some safety margin for inrush and future growth. If the panel requirement is 24 amps, treat that as a continuous load and apply the common sizing rule of 125%: 24 × 1.25 = 30 amps. Transformers are made in standard sizes, and to allow for starting surges and possible expansion, the next standard size above 30 amps is 40 amps. That’s why a 40-amp transformer is indicated. A 20-amp transformer is too small for a 24-amp panel; a 30-amp transformer leaves less headroom for inrush and growth; a 50-amp transformer would be more than necessary.