Quote:
Originally Posted by hedgie
I would expect the external case of any appliance to be grounded, especially a metal case such as the SA STB. In fact I am pretty sure it is a requirement for small appliances to be case grounded.
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No, not anymore nowadays:
The Scientific Atlanta Explorer4200DVB set-top box bears the "nested squares"-symbol of
IEC Protection Class II Device and as such it does not require a connection to electrical earth. Therefore it features an unpolarised two-wire
IEC-60320 C8 socket only. I also somehow recall an old rule-of-thumb that devices with metal cases always required grounding and hence could not achieve a Class II rating; but I know that this is not true any more since at least a decade.
Cutting it short: No, the
STB is not grounded
- apart from the ground provided by the "cable" coming from VirginMedia, which is actually connected to the case (the plug is screwed onto a part of the case which deliberately lacks paint for that reason).
Before adding an extra ground wire, I measured about 1.6V DC and 0V AC between the STB-case and the earth-pin in my electrical socket. I also measured a DC current of a few Milliampere. I forgot the actual number, but it was small. It must be, since it does not trigger the RCD that I bought and plugged in between the socket and the STB now.
I wonder whether I should just continue to enjoy hum-free bliss or whether I should talk to VirginMedia about it. However, I doubt any replacement STB would do better anyway, so I guess I ignore it for now.
However, my limited electrical knowledge is restricted to "White Goods" only, so I would highly appreciate any input on the issue from anyone with actual expertise in "Brown Goods" or electronics. Thanks!