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Re: [Amps] *** SPAM *** Re: Safety grounding - was Mains IsolationTransf

To: Gudguyham@aol.com, g3rzp@g3rzp.wanadoo.co.uk, r@somis.org
Subject: Re: [Amps] *** SPAM *** Re: Safety grounding - was Mains IsolationTransformer
From: Peter Chadwick <g3rzp@g3rzp.wanadoo.co.uk>
Reply-to: g3rzp@g3rzp.wanadoo.co.uk
Date: Wed, 5 Jul 2006 16:53:45 +0200 (CEST)
List-post: <mailto:amps@contesting.com>
Lou said:
>If both phases A&B are carrying X amps of current, there is no current flow on 
>the neutral. <
Only if the two loads have identical power factors. If one is capacitive and 
one is inductive, the currents in the neutral won't cancel.
>in which case it would be a dead short which will throw the breaker in a 
>fraction of a second<
OK. We have to consider the possible fault current during the time that the 
breaker takes to open (or not, sometimes!) Interestingly, there was a Boeing 
747-400 had a bit of a problem 10 years ago because Boeing mistakenly fitted a 
25 amp breaker instead of 2.5Amp breaker, and the wiring couldn't handle the 
fault current. So the fuses in out mains plugs have something  like a 60kAmp 
fault breaking capability i.e. they can break a fault current of 60kA. They 
don't get long to do it, obviously!

73
Peter G3RZP
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