ST Class 2 Transformers Signal Transformer / Bel ST Class 2 Transformers provide superior isolation and low capacitive coupling. These split-bobbin, low-power transformers feature a power rating of 1.1VA to 36VA and are available in 60 standard configurations. Signal Transformer / Bel ST Class 2 Transformers are recognized to UL 506 and meet the specifications for UL 1446 (E66312).