On 10/01/11 08:40, nev young wrote:
TVs do not have an earth connection. This is a standard for such devices and has been for over 40 years.
Except the 2 LCD sets I have here, Both LG the NEC plasma I repaired for someone the other month and countless other units I have seen.
In fact if you look at the design of some of the lower end sets with the single tin can holding both the SMPSU and the inputs (some of which have exposed metal) then you would see that it actually would be a fair amount of effort to make them Class II.
Now if we were talking about CRT TV's which I made the assumption hardly anyone is still using...then yes it was very common for them not to have a earth connection because the nature of the most common method of powering the things (i.e shoving mains through a bridge rectifier which has it's negative side tied to Chassis) means that the chassis can sit at what looks roughly on most meters like half mains potential. In fact it is more like half wave AC at roughly -320volts. This is why if you are particularly well grounded you will feel a bite from the antenna socket of many CRT TV sets, all chassis grounded connections should be decoupled but naturally you often see some leakage current.
So if you were using a CRT set then maybe that is what you saw..but as an ex electrical engineer I would have expected you to know that wasn't static :)
There should be no connection between earth and the output of a laptop power brick.
Except the Dell PA-1650-05D I just randomly picked from the top of the spare adaptor pile which has a nice connection from the outer ring of the DC connector to the earth pin. Maybe I was just lucky there so let's try another one, this time a HP part number 393954-001. Yup the same :)
Many devices are not earthed by design. At least that was the case when I was an electrical engineer. Things may have changed since I became a software engineer.
Yes Correct. Class II devices (double insulated) do not require an earth connection and often are not earthed by design...not all devices are Class II