The Relay 004 is a 120 VAC coil DPDT (double pole double throw) relay that is used to isolate electrical loads and allow higher current ratings than the on board relays found on Tekmar® controls. It can be used in applications ranging from doubling the capability of a single output (e.g. energize a pump as well as provide a boiler demand from one output) to allowing a pump to be used that draws more than the control's specified relay rating. The 004 relay uses a 120 VAC coil that once energized, closes 2 normally open contacts and opens 2 normally closed contacts.