Newsgroups: alt.engineering.electrical
Subject: Re: wire gauge
References: <[email protected]>  <[email protected]>
"Rooh"  writes:

> thanks for your reply. i need to know the wire gauge for neutral wire.
> does it carry the thrice current of a power line.

When the load is perfectly balanced on the three phases there 
will be no current flowingf on the neutral wire. 
When the load is not balanced, there will be current floating 
on the neutral. With pure linear loads the neutral current 
can be up to the current of one phase (the current of phase 
carryign the highest current, think situation where power is
taken only fron one phase). If the load is non-linear then 
the the neutral current can in extreme case be the sum of 
all phase currents (all load third harmonic). 
Dimmers and switch mode power supplies without 
power factor correction do generate a large number of 
odd-order harmonics (worst is third). For example with 
large dimmer loads the usual practice is to specify the 
neutral conductors at 130% of phase conductors 
(rated for 130% of nominal phase current).      

 
> [email protected] wrote:
> > On 4 Jul 2006 12:24:41 -0700, "Rooh"  wrote:
> >
> > >Hi All
> > >i need to calculate the wire gauge for 3 phase system ( 3 x 220 power,
> > >1 neutral and 1 ground) and 150 Amp balanced load ( 50 Amp on each
> > >phase). what should be wire guage for 3 phase wire and specially for
> > >neutral and ground. can any body tell me about calculations.
> > >looking forward towards positive response
> > >Regards
> > >Rooh
> >
> > The short answer to your question is 6 ga copper (50a per phase) but I
> > am not sure the question is right.
> 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/