Question:  Is it necessary to have intercom power on both sides of an MT-1 Interface in order for it to function properly? We have a EF-701M 4-wire interface on one side so that side of the MT-1 has no intercom power.
Answer:  Yes, the MT-1 does require PL power on both sides of the interface in order to function properly as power is not passed thru the device electronics.
One system isolator circuit card must be used for each channel of the intercom systems being connected together. The system isolator card becomes the termination for the connected channels from each system. The station- or power-supply-
based terminations for these channels must be turned off.
Power is provided by the attached intercom stations or power supplies. The MT-1 is intended for standard Clear-Com intercom lines only and cannot be used on “TW” powered lines.