The requirements of UL 1876 cover isolating signal and feedback transformers for use in electronic equipment where only audio, video, and other signal waveforms are transformed. These transformers are intended to provide isolation from circuits that are either conductively connected to a branch circuit supply or connected to secondary circuits involving voltages that are considered to present a risk of electric shock by the nature of their use in an end-product.
ANSI/UL 1876-2011 history
2011ANSI/UL 1876-2011 Standard For Safety For Isolating Signal and Feedback Transformers for Use in Electronic Equipment