AFDD

we are preparing to use AFDD on a wider scale but we find it difficult to justify the very high cost involved.

It's interesting to compare the situation with RCDs - which were similarly expensive when first introduced. The obvious difference is that the early RCDs (or ELCBs) were usually used to cover a complete installation - whereas AFDDs seem (for reasons that still seem less than totally clear to me) seem to be aimed at individual final circuits at most (so you need many more of these expensive beasts for the same effect) - which reduces take-up and therefore evidence of their abilities in practice.

"poor crimp connection"

Which presumably could have resulted in simple resistive heating (as in many reported CU fires) rather than necessarily any arcing.

If it was a series arc, the current would presumably been limited by the load of the appliance itself (unless there were additional faults) - and as most AFDDs don't respond to currents below about 3.5A and most domestic fridge-freezers generally draw a lot less than that, it's certainly questionable whether an AFDD would have responded even if arcing was involved.

There are some interesting videos on youtube showing many AFDDs failing to respond to arcs between two metals -  it seems that carbon (e.g. burnt PVC) needs to be involved .. which again may well not be the case in a series arc of a metal to metal crimp or more generally in a loose terminal connection.

   - Andy.

AJJewsbury said:

Which presumably could have resulted in simple resistive heating (as in many reported CU fires) rather than necessarily any arcing.

Although the overheating sets forth a chain of events that could eventually result in a series or parallel arc?

AJJewsbury said:

If it was a series arc, the current would presumably been limited by the load of the appliance itself (unless there were additional faults) - and as most AFDDs don't respond to currents below about 3.5A and most domestic fridge-freezers generally draw a lot less than that, it's certainly questionable whether an AFDD would have responded even if arcing was involved.

was it a series arc in this case? Did the overheating lead to damage of insulation that eventually led to a parallel arc?

Worth reading the expert report.

AJJewsbury said:

carbon (e.g. burnt PVC) needs to be involved .. which again may well not be the case in a series arc of a metal to metal crimp or more generally in a loose terminal connection

For a single arcing event, perhaps ... but for repeated arcing over time, carbon can build up.

AJJewsbury said:

Which presumably could have resulted in simple resistive heating (as in many reported CU fires) rather than necessarily any arcing.

Although the overheating sets forth a chain of events that could eventually result in a series or parallel arc?

AJJewsbury said:

If it was a series arc, the current would presumably been limited by the load of the appliance itself (unless there were additional faults) - and as most AFDDs don't respond to currents below about 3.5A and most domestic fridge-freezers generally draw a lot less than that, it's certainly questionable whether an AFDD would have responded even if arcing was involved.

was it a series arc in this case? Did the overheating lead to damage of insulation that eventually led to a parallel arc?

Worth reading the expert report.

AJJewsbury said:

carbon (e.g. burnt PVC) needs to be involved .. which again may well not be the case in a series arc of a metal to metal crimp or more generally in a loose terminal connection

For a single arcing event, perhaps ... but for repeated arcing over time, carbon can build up.