Grounding

[sitaramat13]

Here I have some doubts on earthing.
Why neutral is earthed at service entrance panel ?

If it is not earthed , a person won't get shock , even when he comes into contact with live wire , either directly or through an unearthed chassis touching live wire because of some fault and he coming into contact with it.

2. Why electronic subsystems should be enclosed in metallic enclosure? Why can't insulating plastic box be used ? Even when live wire touches enclosure and a person touches it , it won't cause shock in this case. ( EMI/EMC/ESD could be one reason I suppose )

3. In case metallic enclosure connected to safety earth, should signal reference also be connected to safety earth?

[pebe]

[quote]Why neutral is earthed at service entrance panel ?[/quote]
I don’t know which country you live in, but in the UK that is not so. The substation feeding a residential area will output 3phases plus neutral, and the neutral is grounded there. A single phase plus neutral is delivered to each dwelling, with the 3phases allocated to consecutive houses. As each house uses different amounts of power, imbalance currents will flow along the neutral causing a voltage to appear between neutral and ground at each dwelling. So grounding the neutral at each dwelling would cause problems.

[quote]2. Why electronic subsystems should be enclosed in metallic enclosure? Why can't insulating plastic box be used ?[/quote]
Insulated boxes are often used. Where equipment is enclosed in metal boxes it is for the purpose of EMI screening or to give physical robustness.

[quote]3. In case metallic enclosure connected to safety earth, should signal reference also be connected to safety earth?[/quote]
Normally, if a metal box is used, the circuitry inside it will be connected to it. So it is OK to use the box as the common signal point. If it is not connected BEWARE! because the circuitry may be connected to live mains!

[apvkt]

Hi guys,
Thanks for the useful information posted...Plz keep on displaying something new....