Ok, so I'm still a bit confused about the characteristics of the various types of RCDs, i.e. AC/A/F/B. I've concluded that's because there are two classes of effects: a type of residual current that will cause a trip, and a type of residual current that will blind the device against other types of current it would normally trip on. I find that online discussions and 531.3.3 don't clearly distinguish these cases. Can anyone provide, or give a link to, a clear description of what each type RCD is designed to trip on, and what can blind it? For example, might a smooth DC residual current >6ma blind a type A? And if so, is that completely blind, or just blind against pulsating DC (AC still works)? Etc.
The problem is the blinded behaviour is not specified, as it depends on aspects of the RCD design that are not part of the normal use.
So an AC type, may be blinded by DC, but in practice many are not totally blinded unless the DC is smooth, but they are nearly all desensitised to a degree.
An A type is really an AC with a large enough ring core inside that the ripple of unsmoothed DC operates the mechanism, in the presence of the average DC does not saturate the larger core.
Most AC and A types can be totally blinded by a smooth DC, if it ramps up slowly enough.
All the designs for the more complex classifications have deliberate DC sensing with a hall effect sensor.
The problem is the blinded behaviour is not specified, as it depends on aspects of the RCD design that are not part of the normal use.
So an AC type, may be blinded by DC, but in practice many are not totally blinded unless the DC is smooth, but they are nearly all desensitised to a degree.
An A type is really an AC with a large enough ring core inside that the ripple of unsmoothed DC operates the mechanism, in the presence of the average DC does not saturate the larger core.
Most AC and A types can be totally blinded by a smooth DC, if it ramps up slowly enough.
All the designs for the more complex classifications have deliberate DC sensing with a hall effect sensor.
