| phil-news-nospam@ipal.net 2008-03-27, 9:25 am |
| On Thu, 27 Mar 2008 05:21:17 -0700 (PDT) VIDHYA <vidhya36@gmail.com> wrote:
| On Mar 26, 7:06?pm, buttered <buttered.fing...@gmail.com> wrote:
|> VIDHYA wrote:
|> > why we are connecting fuses to phases alone and why we are not
|> > connecting for neutral?
|>
|> for safety purpose
|
| one of our staff said that the neutral is nothing but a current
| returning path, that means just a path to make a closed circuit and he
| added that only a part of the current(for eg.10A entering means only
| 3A will flow thro neutral path)will reach the neutral path.....but how
| this is possible...?if it is a closed circuit means the entering and
| leaving currents are same only.....then how he said a part of the
| current alone returned?if we are considerin that it will b dissipated
| as powerlosses will this condition satisfied....
The neutral normally carries the imbalance current between 2 or 3 phases.
If you have a 40 amp resistive load on phase A, and a 40 amp resistive load
on phase B, and a 40 amp resistive load on phase C, there will be no current
on the neutral. If you shut off the load on 2 of those phases, then you
will have a 40 amp load on the neutral. But one thing a lot of people will
not realize with 3 phase electricity is that if you have the load on two of
the phases (only shut off one phase), you still get 40 amps on the neutral.
And there are cases where you can get _more_ than 40 amps on the neutral,
involving non-resistive loads. This will be harmonic or reactive loads.
It might be simpler to first get a grasp of the concept by studying the
type of single phase wiring used in the USA. It involves 3 wires which
include a neutral and what some people might say is 2 phases which are 180
degrees apart. It is simpler to study this because phase angles let you
avoid doing the trigonometry. It's simple addition and subtraction of the
current. If "phase" A has 40 amps and "phase" B has 30 amps, the neutral
carries the difference of 10 amps.
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2008-03-27-0839@ipal.net |
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