Carrier-current-pilot relaying is the best and most commonly used kind of relaying for
high-voltage lines. A report7 showed that this kind of relaying is in service on lines whose
voltage is as low as 33 kv. It is applicable in some form to any aerial line. Carrier-currentpilot
relaying is preferred to wire-pilot relaying because it is somewhat more reliable and is
more widely applicable. Consisting entirely of terminal equipment, it is completely under
the control of the user, as contrasted with rented wire pilot. Also, the carrier-current pilot
lends itself more conveniently to joint usage by other services such as emergency telephony
and remote trip.