How are limit controls and flame roll-out sensors wired?

Limit controls and flame roll-out sensors are wired in series with each other to ensure that they operate effectively as part of a safety and control system in heating equipment. When wired in series, both devices must be closed (i.e., operational and not tripped) for current to flow through the circuit. This is essential for safety because if one of the devices trips, it will break the circuit and shut down the system, preventing further operation.

This wiring configuration ensures that if either the limit control detects unsafe conditions, like overheating, or the flame roll-out sensor detects a flame outside of the combustion chamber, they will both act to stop the operation of the heating system. This helps to protect both the equipment and the occupants of the space being heated, promoting a safe operating environment.

Wiring these devices in parallel would not achieve the same level of safety; in a parallel configuration, the failure of one device may not affect the function of the other, potentially leading to unsafe operating conditions. Therefore, wiring in series is the correct approach to ensure coordinated safety shutdowns.