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Guest sitaramar
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Guest sitaramar

Dear friends,

Here I have some doubts on earthing.

1. 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?

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1) If the mains neutral wasn't connected to earth, it could float at any voltage. Suppose someone connected a 10kV autrotransformer to the mains and the seondary became shorted to earth? The mains would then float at 10kV above earth, causing fire as the insulation isn't rated to that voltage.

2) Became metal doesn't burn like most insulators do.

3) It depends on what you're doing.

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