Final answer:
In a 4-wire control system, terminals R and Rc typically have a jumper to connect power from a single transformer to both heating and cooling systems.
Step-by-step explanation:
In a 4-wire control system, the two terminals that usually have a jumper at the thermostat are R and Rc. This is typically done to allow a single transformer to power both the heating and cooling systems, without the need for separate transformers for each. The 'R' terminal stands for the transformer, and the 'Rc' terminal stands for cooling. When there is a single transformer in a system, a jumper is placed between these two terminals to connect the power from the transformer to both the heating and cooling control circuits.
In a 4-wire control system, the two terminals that usually have a jumper at the thermostat are R and Rc. The R terminal is connected to the power source and the Rc terminal is connected to the cooling system. When the thermostat is used for both heating and cooling, a jumper is placed between these two terminals to connect them.