How do AFDDs work?

This Q & A is one of the thousands posted in our Technical Expertise area and answered by our Voltimum Experts.

Question:

How do AFDDs work?

Answer: 

AFDDs are circuit protection devices, like miniature circuit breakers (MCBs) and residual current devices (RCDs), although they offer a different type of protection. They are essentially microcomputers that sit with an overcurrent protective device, though they can be combined. They are designed to look for the signature of an electrical arc. Upon detecting this signature becoming distorted in any way, using complex algorithms, the device will operate.

For ‘arc’, you can read ‘spark’ – from a small fault in a circuit between two live conductors or live conductors to earth. These are usually caused by damaged cables, loose connections or some other breakdown in insulation, and they can generate enough heat to start a fire.

Pre-existing devices which are mandatory in the Wiring Regulations – circuit breakers, fuses and residual current devices – may not always respond to the small arc faults which would activate an AFDD.