Valve/Actuator Slave Controls add extra zone capability to 4-zone or 6-zone Master Control Units. Like the Master Controls, they are intended to control Watts Radiant Electrothermal Actuators, or any 24-VAC actuator that draws 5 VA or less. The number of actuators controlled depends on the 24-VAC external transformer (not supplied) powering the system. However, the physical limitation of the Control itself is four actuators per thermostat connection. Up to two additional 4-zone or 6-zone Slave Controls can be added to a Master Control. No field wiring is required between Masters and Slaves simply plug into each other. Each additional 40-VA 24-VAC transformer capacity can control an extra 12 actuators maximum; 18 actuators maximum with an additional 60-VA 24-VAC transformer. Actuators are switched by triacs, for safe, quiet, reliable electronic operation. Mounting is by DIN rail or surface mount to a wall.