Definition of high protective conductor currents

AJJewsbury said:

• Minimum detection capability up to 20 kHz

• Minimum trip threshold of 150 mA above 1 kHz

I'm trying to get my head around what these mean technically (as opposed to physiologically) and how the various limits are interrelated (and perhaps related to EMC/RFI filters in the internal switching units)

Does it say that the trip threshold should be higher than 150mA [minimum being no lower than..] for the sum of all components above 1kHz, up to and including the 20kHz figure?

There can be a lot of switch RF leakage currents to earth as part of the designs that seek to make the supply (live) and return (neutral) conductors 'appear' to be anti-phase at the RF (just as the Yellow transformers convert 110VAC to +/-55VAC, though for sightly different purposes/methods).

Edit: it could be that previous, more simpler designs, were subject to nuisance tripping from those deliberate RF/EMC suppression leakage currents, and the newer types now have their own filters....

Certainly the leakage current from a switch mode power supply is far from simply sinusoidal and contains pulses of both polarities that may be only 10s of micoseconds apart and of very short duration (sub microsecond). If you average these over the period of a half sinewave at 50Hz, you measure a very low residual, as the ups are cancelled by the downs and furthere more, for say 90% of the time there is nothing there at all....  A traditional mechanical balance trip RCD sort of did this for free as the short spiky pulses simply could not get the armature moving, giving a natural low-pass (HF reject) effect.
A first generation electronic RCD however uses a comparator that on-chip has transistors that certainly can change state at the same sort of speeds as those in the SMPS, actually faster probably, being as large power devices are slower due to increased transit times than the smaller devices on-chip.

Therefore there has to be a deliberate low pass filtering added between the sense coil and the comparator/ amplifier to roll-off the unwanted response to those sharp spikes, to make the RCD behave more calmly and in a similar way to a good old mechanical trip.
This expectation of a roll-off by 5 (about 16dB) between 50Hz and 1kHz is an attempt to  recognize and accommodate the sort of filtering needed to avoid tripping out when things are actually working as they should. It also helps to reduce the mis-firing on other one shot transients such as arcing light switches.

There is a certain irony that in an AFDD that high frequency sensitivity has to be build back in, but then tamed by a multiple 'if this and that but only when this happens too' type of algorithm and of course sensing the line as well as the  imbalance currents.
Mike.

After posting, I did some extra web searching, as you do ;-) 

I found a quite good tech note from Schaffner on the RS web site that provides a good bit of background (and slightly slides past other nuance aspects) on Low Leakage current EMC filters with full RCD compatibility   I Also found Hager's "Why Use Type B HP RCDs for Heat Pump Applications" which has comments about the VDE B+ standard.

The main clue is it's the "Type B" problem of anything with switch mode electronic loads which [could] effectively create (on an average, 20ms cycle) a DC load through the residual/leakage sensing coils. The 'could' part is that most of the current is very high speed switching transients, which if not internally filtered in the circuit breaker device look like live leakage (up to a point where the equipment needs to filter as well, no doubt also for RFI reasons). 

The nuance bit that I hadn't implicitly realised is that the electronic device's diode rectifier, and capacitor, has a store and delay effect on the way supply current is converted to leakage current, such that from the supply side the leakage is in phase (goes through the expected rectifier phase diodes), but on the load side it is, on average, DC.

The Schaffner fig 1 shows the leakage paths. Diag 4 shows the RCD tripping, diag 6 shows a situation where the equipment switching currents are too high (without filter, labels in German;-) and then diag 7how their filter saves the day on the equipment side and stops nuisance tripping relative to a type B RCD..

After posting, I did some extra web searching, as you do ;-) 

I found a quite good tech note from Schaffner on the RS web site that provides a good bit of background (and slightly slides past other nuance aspects) on Low Leakage current EMC filters with full RCD compatibility   I Also found Hager's "Why Use Type B HP RCDs for Heat Pump Applications" which has comments about the VDE B+ standard.

The main clue is it's the "Type B" problem of anything with switch mode electronic loads which [could] effectively create (on an average, 20ms cycle) a DC load through the residual/leakage sensing coils. The 'could' part is that most of the current is very high speed switching transients, which if not internally filtered in the circuit breaker device look like live leakage (up to a point where the equipment needs to filter as well, no doubt also for RFI reasons). 

The nuance bit that I hadn't implicitly realised is that the electronic device's diode rectifier, and capacitor, has a store and delay effect on the way supply current is converted to leakage current, such that from the supply side the leakage is in phase (goes through the expected rectifier phase diodes), but on the load side it is, on average, DC.

The Schaffner fig 1 shows the leakage paths. Diag 4 shows the RCD tripping, diag 6 shows a situation where the equipment switching currents are too high (without filter, labels in German;-) and then diag 7how their filter saves the day on the equipment side and stops nuisance tripping relative to a type B RCD..