Not all transformers are equal – and this one is the most powerful transformer we offer! NuTone® transformers feature an easy-to-install lock-mount or wall-mount that can reduce installation time by 25%. An additional unique feature is the thermal cut-off switch designed to shut off the door chime system in the event of excessive temperature. NuTone® saves you time and money! https://www.broan-nutone.com/getmedia/9e2fbc80-65f8-434c-9cd7-c43b2e1350db/Installation-Guide-C905-C907-C909-C915.pdf?ext=.pdf