Chassis Model RPM-4 has provisions for 4 relays. One side of each relay coil is terminated on same terminal, eliminating the need for bussing. This unit has painted steel chassis with rugged fiberglass printed circuit boards. All relay contacts are clearly silk screened on each PC board for easy circuit wiring, and are terminated on barrier-type screw terminals to prevent accidental shorting. This chassis is equipped with insta-mount tape for quick and easy installation on most surfaces.Relay chassis and relays are ordered separately so unused chassis sockets can be saved for future expansion.