My definition is quite simple, DC is a relatively constant voltage or current, which does not vary with time, in other words, a battery.

Shades of the old "direct current" vs "continuous current" word war of yesteryear. I think the outcome was that d.c. could include ripple (i.e. could include a waveform, but overall it didn't cross zero - i.e. the polarity never alternated) while c.c. was your battery output. But the exact words don't matter as long as we userstand the meaning. Continuous current seem to be out of fashion these days so we have d.c. (sorry DC) and ripple-free DC.

needs a manufacturer to describe how they think this is a problem

I agree - there's still far too much confusion at the moment.


So far it seems to me that there might be several different effects/symptoms/problems going on. There's the issue of DC saturating the coil and blinding the RCD to real faults (for which one fix seems to be a B-type RCD), But there also seems to be a separate issue of the fault current itself not being a complete a.c. waveform - e.g. a L-PE fault after a rectifier - which (allegedly) AC RCDs aren't guaranteed to be sensitive to. On a TN system I'd imagine that a L-PE short after a rectifier, if the RCD or OPD didn't disconnect, would blow the rectifier to smithereens in pretty short order and likely achieve some kind of disconnection fairly quickly anyway. On a TT system with potentially very low earth fault currents, it's seems possible that we'd end up with an uncleared fault. That I think is the sort of thing they're pushing A-type RCDs for.


   - Andy.

My definition is quite simple, DC is a relatively constant voltage or current, which does not vary with time, in other words, a battery.

Shades of the old "direct current" vs "continuous current" word war of yesteryear. I think the outcome was that d.c. could include ripple (i.e. could include a waveform, but overall it didn't cross zero - i.e. the polarity never alternated) while c.c. was your battery output. But the exact words don't matter as long as we userstand the meaning. Continuous current seem to be out of fashion these days so we have d.c. (sorry DC) and ripple-free DC.

needs a manufacturer to describe how they think this is a problem

I agree - there's still far too much confusion at the moment.


So far it seems to me that there might be several different effects/symptoms/problems going on. There's the issue of DC saturating the coil and blinding the RCD to real faults (for which one fix seems to be a B-type RCD), But there also seems to be a separate issue of the fault current itself not being a complete a.c. waveform - e.g. a L-PE fault after a rectifier - which (allegedly) AC RCDs aren't guaranteed to be sensitive to. On a TN system I'd imagine that a L-PE short after a rectifier, if the RCD or OPD didn't disconnect, would blow the rectifier to smithereens in pretty short order and likely achieve some kind of disconnection fairly quickly anyway. On a TT system with potentially very low earth fault currents, it's seems possible that we'd end up with an uncleared fault. That I think is the sort of thing they're pushing A-type RCDs for.


   - Andy.