| phil-news-nospam@ipal.net 2008-03-26, 9:25 am |
| On Wed, 26 Mar 2008 06:30:11 -0700 (PDT) VIDHYA <vidhya36@gmail.com> wrote:
| why we are connecting fuses to phases alone and why we are not
| connecting for neutral?
When fuses are involved, the fuse blowing out on the neutral can create
a very unsafe condition. Search for "broken neutral" and "loose neutral"
and read about hazardous conditions when just the wires come loose. You
could be subjecting a 230 volt device to 400 volts when the neutral is no
longer able to conduct, but at least 2 other phases can.
It is usually permitted to disconnect the neutral via a circuit breaker.
The circuit breaker must be designed for such a purpose. It must ensure
that it disconnects the neutral last when opening, and connects it first
when closing. Fuses cannot do this. Only special 4-pole breakers can.
Normally the neutral is grounded and does not need to be disconnected.
If you have a situation where there could be excessive neutral current,
such as harmonics, that needs to interrupt the power, this should be done
by using a current transformer sensor on the neutral that trips breakers
on the phase lines. Note that some 4-pole breakers may include current
sensing on the neutral, and some may not.
--
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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-2008-03-26-0857@ipal.net |
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