Production of circuit breakers able to detect and isolate arcing in aircraft wiring is being held up by delays in agreeing an industry standard for the devices.

Flight testing of prototype arc-fault circuit breakers by the US Navy and Federal Aviation Administration has so far produced no failures or false trips.

Behind the delay is a lack of agreement on whether the devices should protect only against high-current arcing caused by wire-to-wire or wire-to-airframe contact, and most likely to cause a fire, or whether they should also handle low-energy arc faults, such as connector problems. These are harder to detect and increase the possibility of "nuisance tripping".

Prototypes produced by Eaton Aerospace and Hendry Telephone, optimised to detect high-energy arcing, are being flight tested in an FAA Boeing 727 and US Navy McDonnell Douglas C-9. Eaton says its device is ready for production as a replacement for current circuit breakers, but it is awaiting approval of the standard, expected last October and now scheduled for this October, but which is likely to slip again.

The breakers detect the characteristic "signature" produced by wire arcing. Eaton says its one device is programmed to recognise arc-fault waveforms in "thousands" of wiring installations. The company is concerned that, if the eventual standard calls for detection of low-energy arc faults, then different devices will be needed for each wiring type, increasing cost.

Source: Flight International