such that the total protective conductor current is likely to exceed 10mA,
Is that
exceed 10 mA when the circuit is functioning normally ( current in CPC being due to filters and other capacitive effects ) ...
Yes, it is specifically for equipment with high leakage current - typically lots of filtering (eg capacitors between line(s) and earth). With such equipment, there is a risk that the exposed conductive parts of that (or other equipment on the same circuit) could rise to a dangerous voltage with sufficiently low impedance to cause a shock hazard.
Hence the "high integrity" earth connection to ensure that such a loss of earth fault is "unlikely".
In the specific context, with a standard RFC (all cpcs into single terminals), then a single terminal coming loose could lose earthing for a double socket or even the whole ring if it's at the earthing bar in the CU. By requiring every cpc to use a separate terminal, you need two such faults before there is complete loss of earth to any point.
Does this have any influence on manufacturers to design double insulated equipment ( no earth required ) that when powered up has a metal case parts that gives a "tingle" to the touch ? If the case was connected to earth via an amp meter and the leakage found to be higher than 10 mA then ( apparent ) the equipment would require a mains supply with a high integrity earth system.
Yes, I believe that would be the case. But I don't think it's related to going DI.
Do manufacturers choose to go double insulated ( albeit with a tingle touch ) so they can avoid restricting use to supplies with high integrity earths.
( And without an earth how do the manufacturers filter out mains borne voltage spikes. ? ? )
"Small" equipment doesn't usually have much leakage - some years ago I came up against this when my employer was having a new warehouse built. The electrical contractor was being "a bit anal" over the electrics - claiming he could only fit single sockets (not double) and would not fit extra (to give the number of outlets requested) without significant extra costs. So I knocked up a test rig (extension lead with multimeter in the earth connection) and tested a representative sample of all our kit - I couldn't find a single item with any significant leakage.
On the other hand, once you go up in size a bit ...
I dismantled our old failed UPS from the server room - cable went in the copper box, steel in the steel pile, only a relatively small amount of "electronic waste" left). That had some very sizeable input filters in the bottom of the cabinet - I think I'll see if we still have them lying around and test them.
I suspect the main reason for going DI is simply to avoid the need for an earth at all. Allows the use of a "figure of 8" 2 pin inlet, and no worries about (eg in the case of hand tools, lawn mowers etc) the risk of exporting an earth to a location where it may not be "earth". Not to mention, if you are holding a metal cased drill at the end of a very long extension lead, in the event of a fault it's possible to get s situation where the body goes to half the mains voltage (so 120V around here) but the upstream fuse could take a while to blow.
And without an earth - you don't filter out any spikes ! If there are no other connections to the equipment then you gain a lot of immunity to common-mode surges and spikes. An example of this is phones.
An ex boss lived in the country, all overhead services, and prone to thunderstorms. They would lose the fax machine and computer modems on a regular basis - but never any "ordinary phones". The phones weren't affected by the common mode surges because there wasn't a path for any current. Fax machines, modems, cordless phone bases all had a path via earth for incoming surges and so suffered.
I had suggested he really needed to route the phone lines close to the mains supply, and fit "whole house" surge protection at that point - but it never happened.
With the stack of kit under the TV ...
Well that's all linked by cables - so if any item is earthed then everything else will be earthed through it. Potentially one lot could be earthed up the aerial lead, via the LNB or dist amplifier, and down another aerial lead to another set of AV equipment that is earthed !
