Answer / cnu

in the measurement of voltage in any circuit we measure the
voltage of one conductor with respect to another.

In DC supply we have two conductors namely Positive(+) and
negative(-). if we consider 48V DC across the two
conductors, then if we measure the value on the positive
conductor with respect teo the negative conductor the value
is +48V. if we measure the same value on the negative
conductor with respect to the positive conductor then the
value will be -48V. this 48V is the instantaneous value of
the DC supply.

Where as in AC we have two conductors namely Phase and the
Neutral. always the Phase constitute the current path and
the neutral forms the return path. we say that the AC
voltage is sinusoidal. that is it varies from positive to
negative when seen with respect to the neutral.

its impossible to measure the instantaneous value of the AC
supply bcoz it keeps on continuosly varying. so for the AC
supply we consider the RMS value (Root Mean Square Value)
as the voltage of the supply. so in this case there is
always the same value when measured with respect to any
conductor. so the AC voltage does not have polarity.

Answer / naren

when we are measureing dc voltage in negative circuit we
have -48V DC , but in AC there is no negative supplay and
hance we get 48V AC from Phase to Nutral as well as Nutral
to Phase.

Why neutral has to switch on-off with phase in TN IT TT systems i.e neutral should be taken as fourth pole

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