Quote:
Originally Posted by mhennessy
AFAIK, there are no safety requirement for the signal earth to be bonded to the chassis, and something like the outer shell of a phono socket, for example, would not be expected to carry the 25A of an earth continuity test ...
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Doesn't it seem a bit unlikely that there are formal requirements for us to be protected from electric shcok when we touch the chassis but these requirements don't apply when we touch a plug-and-socket connector (my rather ordinary Neutrik phono plugs all have metal shells connected to the phono outer) ? The plugs are designed to be touched, in fact gripped quite hard.
I'm not an equipment manufacturer so I haven't taken out a second mortgage to buy a copy of EN 60065:2014 or its replacement EN 62368. But I do have a copy of its predecessor EN60065:2002. That says, in Section 8.5, and I quote
CLASS I apparatus shall be provided with a protective earthing terminal or contact to which the protective earthing contacts of socket-outlets, if any, and ACCESSIBLE conductive parts shall be reliably connected.
There are some exclusions relating to any accessible parts which are Class II insulated or which are protected e.g. by an intermediate screen, but I don't think either of these apply to phono socket outers. So it's pretty clear that phono socket outers must be reliably connected to the protective earthing terminal (commonly the centre pin on an IEC inlet). I would argue in court that a pair of 35A (cw)/350A (pulsed) diodes in parallel constitute a reliable connection. I'd be more nervous about relying on a single metal film resistor in the event of the mains driving a hundred amps or so through it.
Cheers,
GJ