Definition of high protective conductor currents

Thanks guys - this has been very useful!

I notice Mike's graph is based on pain rather than effects that cause permanent damage or Ventricular fibrillation, so maybe there's still a bit of room for debate there (I'm sure I recall a 400Hz system for aircraft that was meant to have a reduced shock risk). But all the same we still have no solid evidence that higher frequencies can be safely ignored.

For me that calls into question the effectiveness of specifying 30mA RCDs for additional protection in this case. I guess in the case of direct contact with live conductors on the a.c. supply side the residual current will still be 50Hz and so the RCD should trip as normal. But for other cases - e.g. a broken c.p.c. (single fault) the current flowing from the equipment case via a victim could well have high frequency high current components the RCD would ignore, but could still prove fatal. So my first question - whether we should have high integrity c.p.c.s seems justified,

Or just design out the need for a RCD of any kind

Indeed - that was my starting point. I've still got an open question with the manufacturers whether their statement that ALL the heat pumps need an B-HP type RCD should be read as requiring RCD protection where BS 7671 makes no such demands - or whether they just meant "where an RCD is present it shall be a B-HP type".

Given the supply wiring is fixed, unlikely to be damaged and everything else is contained within an earthed metal box, the need for additional protection seems very small.

In the mean time I'll be looking to ensure my setup complies with 543.7...

   - Andy.

ensure my setup complies with 543.7...

A sensible precautionary approach.

I notice Mike's graph is based on pain rather than effects that cause permanent damage or Ventricular fibrillation, so maybe there's still a bit of room for debate

Oddly its not an area that most folk are keen to research and there is not a lot out there  !!

This from ICNIRP may be of interest to you. 

GUIDELINES FOR LIMITING EXPOSURE TO TIME-VARYING ELECTRIC AND MAGNETIC FIELDS (1 Hz TO 100 kHz)

While predominantly about radiation, it does cover direct contact as well.

Note however that the numbers here are a factor of 30 or so lower than those used by BS7671 and the standards from which it derives its specifications... And, given results of rather worryingly simple/ dangerous tests like this, perhaps correctly so.

https://pmc.ncbi.nlm.nih.gov/articles/PMC2763825/ scroll down to the rather childish picture of someone with feet in two buckets of water.

Fresh (not salt) water with conductivity of 320 µmho/cm filled each bucket to a level near the hip. It was found that electrically induced muscle contractions were greatly modified by leg position in the water.

Initial testing has shown that with 3.05 V (60-Hz AC rms) applied between the plates, a current of 8.65 mA flowed, resulting in involuntary flexion of the knee to 90°. This flexion could not be overcome with voluntary effort. ..

Now that's a voltage most regulation writers feel is safe, even near a swimming pool  ;-)

Then there are folk measuring people and arguing the existing body resistance model is wrong (well, more charitably, incomplete perhaps)

Assessment of Human Body Impedance for Safety Requirements Against Contact Currents for Frequencies up to 110 MHz

It is fair to say, the science is not settled. I'd prefer screened or armoured  cables for now.

Mike.

The requirements are nothing to do with the 'shock', rather it's nuisance tripping and 'blinding' (failure to trip) of the circuit, that is being coordinated.

That's a bit sweeping - why do we worry about it tripping (or not) if the currents under discussion are not potentially a threat - put another way, if electric shock was not a thing, we would not need CPCs, let alone RCDs that tripped on earth currents,  at all. 
Mike.

That's a bit sweeping - why do we worry about it tripping (or not) if the currents under discussion are not potentially a threat - put another way, if electric shock was not a thing, we would not need CPCs, let alone RCDs that tripped on earth currents,  at all. 
Mike.

Let's get back to the start. The question was about the technical spec of an RCD.

That spec (the special aspects) is not about the shock potential for the human, rather it's about all the side effects of the load and how it interacts with the RCD's detection apparatus, and the coordination between the two.

Things like needing to be a type B, and needing certain rejection characteristics. None of those characteristics, as best as I can see, are anything to do with effects on the human, and far more to do with a coordination between EMC/RFI requirements, filtering capabilities at the load and filtering within the RCD. The EMI/RFI filtering is the one that creates earth leakage that looks like residual current, and we need discrimination between real fault leakage and EMC/RFI leakage.

Philip Oakley said:

and we need discrimination between real fault leakage and EMC/RFI leakage.

I think there could be some cross-over there. Normally we'd expect a 30mA RCD to provide a decent level of protection against shock in a wide variety of circumstances - including the single fault condition of a broken c.p.c. where "protective conductor current" becomes the same as shock current. If we've now got (non-standard) "30mA" RCDs that actually allow 150mA to flow without disconnecting (if not 50Hz components) it feels to me we might have lost something here.

   - Andy. 

A 30mA 50Hz shock (the electricians classic shock) is not the same, physiologically, as [say] a 60kHz 30mA 'shock' leakage. The RFI leakage could be (depending on switching frequency design) anywhere between say 8kHz and 200kHz (or higher).

Then there is the "phasing effect" that it is capacitively coupled, and from the leak perspective, it's always in-phase with itself, but 90 degrees out of phase with the switching clock, and has no phase at DC, making discussions hard as each group uses it's own 'reference' concepts, while ignoring those [unappreciated] aspects from the other group.

It's real tricky stuff. (see https://tv.theiet.org/?videoid=1327, and my comment about 2/3rds the way through)