Answer / cnu

Basically a device is earthed to avoid any stray
circulating current that appear on the body of the device
operating with an AC supply.

since AC creates an alternating flux. this changes in flux
induces stray currents in the metallic body of the devices.

When coming to DC, since it is a constant voltage it does
not produce flux change to induce any currents so earthing
is not required for a DC battery.

Answer / prasoon

In a HV Sub station, 220 Volt system is not earthed to
avoid mal operation of DC controlled electrical elemnets in
case of a earth fault.

50 Volt system is earthed (-ve). This is done as 50 volt
system is used for electronic circuits where -ve voltage is
required to opearate npn transistors.

Answer / aamod tripathi

To avoid circulating current in DC system.

Answer / owais chaudhri

b/c there is already availabe zero potential in batry
(ie -ve terminal).

Answer / kanth

there is no need of earthing fo Dc systems
and in AC only earthing is needed
bcoz power generated from generators and ttransfer from
transformers ,so transrormers neutral's earthing has done
(in star-star or delta-star trafo)so phase currents goes
directly though earth or in neutral as a returned path to
transformer.
so we r using neutral for return path and earthing for
safety

for 12KW motor which cable size has to select for ex.10 meter.

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