DC-Blocking Lightning Arrestors

Prefer a DC-blocking arrestor unless you need DC current to pass along the coaxial cable.

Non-DC blocking arrestors are used when DC current needs to pass along the coaxial cable, such as when feeding power to a tower-mounted pre-amplifier. Non-DC blocking arrestors are inferior because they cannot divert all of the strike voltage to ground without sharing a significant portion of it with the equipment that is being protected.

DC blocking arrestors use a capacitor to block DC current flow along the center conductor of the coax. There is no center conductor continuity from connector pin to connector pin. This internal capacitive coupling prevents the sharing of low-frequency surge current with equipment, and limits the throughput energy to only the amount that can be coupled by the electrostatic field in the capacitor. The result is far less surge current than with a non-DC blocked arrestor.

If DC power on the coax is needed, there are combination devices which couple a DC blocking arrestor with a “bias T” (DC injector/pick-off). This allows the DC to be injected/picked off without giving up the advantage of a DC blocking arrestor. When DC power is not needed to feed tower-mounted devices, DC blocking arrestors are usually preferred.