Edwards 590 Series Class 2 Signaling Transformers are easy to install, low voltage power sources for residential, commercial, and industrial uses. Mounts in a standard 1/2" (13mm) knockout or surface mounts using the provided foot mounts. These transformers are suitable for mounting in both plastic and metal back boxes. May also be used with the 593 transformer plate for enclosed mounting in a standard two gang outlet box. The 591 transformer is suitable for standard doorbells and chimes in residential and commercial applications requiring 16 volts AC.