The SP-8 Heavy-Duty Surge Protector is a very effective protection system for the RFC-1. Field data indicates that it reduces lightning damage by about 98%. Unfortunately, this is small consolation for those 2% of installations that get damaged.

Almost every case we have seen of lightning damage to systems using the SP-8 was caused by arc-over in the control relays. The insulation in the control relays between the contacts and the coil is effective to about 4500 to 5000 volts. Above that value, a flash-over will occur from the contacts to the coil. This introduces high voltage to the ICs on the relay panel, the line driver in the RFC-1 (U6) and to the power supply. Sometimes only U6 in the RFC-1 is blown. In more severe cases other ICs are lost as well.

It is fairly simple to prevent a recurrence of this problem by identifying which control source is generating the high-voltage transient and installing varistors on the control leads to that device. In most cases, the source will be the transmitter. When a tower gets hit by lightning, the entire transmitter can be elevated above ground by hundreds or even thousands of volts.

The varistors should be installed near the RP-8 panel as shown below. It is often convenient to solder one side of the varistors to a piece of large copper wire (#10 or #12) and connect both ends of this wire to the rack in which the RP-8 is mounted.