Electronic controllers mounted in a cabinet near an intersection regulate traffic signals. Long wires carrying AC power necessary for the electronics to do its job can also conduct utility line disturbances (due to nearby switching, phase imbalances and load changes) into the controller power supply inputs. These, and the wires connecting the controller to the lights being controlled, can act like antennas picking up electromagnetic transients from a nearby lightning strike. Energy from lightning can also be readily coupled into lines buried a few feet underground and travel to the controller interfaces. The transient’s current, voltage and energy can easily overpower circuits not designed to handle them resulting in equipment disruption, damage or destruction. Transient overvoltage protectors designed to withstand and reduce transients to tolerable levels can be placed at the equipment between the equipment and the long wires to protect susceptable circuits.
For the AC power line, a 30 Amp protector is recommended because of the current draw required by the high intensity signal lights. Select the control loop protector voltage to equal or exceed the loop power supply maximum voltage. Loop protectors are available with L-L protection, e.g. CLPS421BEXXXX or L-L and L-G, e.g. a 420E2XXG. These loop protectors have different connection interfaces providing ease of installation or certain applications. All these protectors use rugged, high energy input circuits to which the field wiring is connected. Also, they utilize isolating series impedances coupled with rapid response output protection circuits to which the inputs to be protected are connected.
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