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AFDDs - are they sensitive to upstream arcing?

AJJewsbury
It's occurred to me that if AFDDs work by spotting distortion in the a.c. current waveform that's passing through the device, then they're likely to see the same effect if series arcing is occurring upstream (with a decent sized load downstream).


If that's the case a decent DNO's crackle could trip out a significant number of final circuits if they happened to be loaded at the time.


Or are AFDDs cleverer than that? (e.g. do they look for an undistorted incoming voltage as well as a distorted current?)


As many of the dimming and flickering I've seen has been down to DNO loose connections, there could be a lot of nuisance tripping with these new devices if my worry is correct.


  - Andy.
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    I have read another paper that suggests that AFDDs sense RF around 23 MHz on cables. Why this frequency or anything else is missing but I do wonder if these devices have passed an RF susceptibility test, as I cannot imagine that a nearby transmitter might not be a serious problem. I cannot see any way that an AFDD could be made sensitive to the current flow (direction does not indicate the source) and a fault upstream and a resistive load must be detected. One paper does admit that a steady load plus an arc fault current is very difficult to detect, so there seems to be an assumption that every circuit has only one load, which is not true at all in the UK. That is probably why an AFDD per circuit is mandated, not one upfront device. It also means that UK ring and radial circuits will probably not be well protected, as both are designed to have multiple loads. Oops! More testing needed....
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  • 0
    I have read another paper that suggests that AFDDs sense RF around 23 MHz on cables. Why this frequency or anything else is missing but I do wonder if these devices have passed an RF susceptibility test, as I cannot imagine that a nearby transmitter might not be a serious problem. I cannot see any way that an AFDD could be made sensitive to the current flow (direction does not indicate the source) and a fault upstream and a resistive load must be detected. One paper does admit that a steady load plus an arc fault current is very difficult to detect, so there seems to be an assumption that every circuit has only one load, which is not true at all in the UK. That is probably why an AFDD per circuit is mandated, not one upfront device. It also means that UK ring and radial circuits will probably not be well protected, as both are designed to have multiple loads. Oops! More testing needed....
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