The Relay 004 is a 120 V (ac) 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 V (ac) coil that once energized, closes 2 normally open contacts, and opens 2 normally closed contacts.