The breakaway cable has a two-fold purpose. One end is attached to the brake on the trailer and the other end to a suitable point on the towing vehicle.
In the event of a trailer becoming unhitched while the vehicle and trailer are in motion, the breakaway cable will apply the trailer brake to allow the trailer to come to a halt just before the cable snaps and the trailer separates completely from the towing vehicle, thus minimising the risk of a runaway trailer on a public highway.
The law in the UK requires all trailers with brakes, over 750kg GVW and up to 3,500kg GVW and built on or after October 1 1982, to be fitted with a safety device to provide protection should the towing vehicle and trailer separate.
Using a breakaway cable ensures compliance with this law.