[Amps] Electrical Distribution Methods

[TexasRF at aol.com]

Hi Paul, probably showing my ignorance here but isn't there a 120 degree  
phase difference between any two legs of a three phase power distribution  
system? 

Seems that might pose a problem connecting the single primary of a  
distribution transformer.
 
73,
Gerald K5GW
 
 
 
 
 
 
 
In a message dated 10/15/2013 7:40:04 A.M. Pacific Daylight Time,  
w9ac at arrl.net writes:

Peter,

That's a good explanation.

> With  Protective Multiple Earthing, provided there is enough distributed 
>  grounding of the neutral, that isn't a problem.

That's an area of  concern of mine in one application of the U.S. 
electrical 
distribution  system.  Many of us have likely noticed that one terminal of 
a  
pole-mounted utility company residential split-phase transformer is  
connected to one of three hot phases in a multi-phase distribution system  
--  
or single-phase distribution where the one hot phase is split  from an 
upstream three-phase source.  In both cases, the primary  return is 
connected 
to the Multi-Ground Neutral (MGN) messenger cable (AKA  "strand").  That 
cable is bonded and earthed down each and every  utility pole.  This cable 
may also serve double-duty for attachment  of either CATV or telephony 
cables -- or where telephony and CATV is  separated on different strands, 
they are periodically bonded  together.

It's unnerving to think that the bare copper bus wire that  runs down each 
pole is really connected to many, many KV and the only  thing keeping a 
barefooted kid safe when s/he touches an accidentally  lifted/unearthed 
ground wire is that (hopefully) the MGN cable strand has  excellent 
connectivity to earth on many poles up and downstream from the  pole in 
question.  I understand as a matter of economics it must be  this way for 
single-phase distribution as is common in rural areas.   But when a 
240V/120V 
split-phase transformer is hung on a three-phase  pole, why can't the 
primary 
connect between two phases instead of one  phase and the MGN?  I can't see 
a 
direct economic impact in this case  apart from perhaps better lightning 
mitigation when one side of the  utility transformer primary is grounded.

Sorry for drifting the subject  off even further (notice the new subject 
line) but it's been a nagging  question of mine.  In a past life, I was 
Director of Engineering for  several telecom and broadband firms and this 
issue was raised from  time-to-time (usually when a cable tech was injured) 
with no clear answer  ever obtained from the utility companies.

Paul, W9AC


-----  Original Message ----- 
From: "peter chadwick"  <g8on at fsmail.net>
To: <amps at contesting.com>
Sent: Tuesday,  October 15, 2013 9:49 AM
Subject: Re: [Amps] More on two pin  220vac


> The neutral is probably grounded at the distribution  transformer. That's 
> likely to be a Y secondary and the centre point  is 'grounded' and forms 
> the neutral. Depending on the load and how  much resistance there is in 
the 
> neutral, at any point along the  distribution, the neutral voltage will 
> rise above ground to some  extent, so quite often, additional grounds are 
> provided for the  neutral. The problem comes if the neutral is ruptured: 
> then the  'load' side of the break is connected through the stoves, A/C, 
> radio  gear etc to the live side of the line and the neutral, under these 
>  fault conditions is up at line voltage with respect to ground.
>
>  With Protective Multiple Earthing, provided there is enough distributed  
> grounding of the neutral, that isn't a problem. Where the neutral is  
> connected to the house ground wiring, then you can get a problem,  
because 
> the stove, A/C etc would love that ruptured neutral to have a  good 
ground 
> connected to it. If that ground is the external radio  ground, all the 
> fault current wants to go there through the cable in  the wall and the 
> transceiver power cord which can't take 50 or 100  amps....for very long, 
> anyway.
>
> So here, it is allowed  for the property earth to be separate from the 
> supply 'earthed'  neutral - and that's much safer in the ruptured neutral 
>  situation.
>
> But different countries have different methods. At  one time (and maybe 
> even now) some outback properties in Australia  used a ground return 
> instead of a neutral.....
>
> As  they say, 'there's more ways than one of skinning a cat' - although 
my  
> cats don't believe in any of them!
>
> I think Charles  should firstly check the schematic to make sure that 
there 
> is nothing  getting power from one side of the line and chassis - 
although 
> that's  not been allowed for years and the amplifier probably wouldn't 
work 
>  anyway. The use a meter to check that BOTH mains leads are a very high  
> resistance to chassis - many megohms.
>
> Secondly, check  the wiring to make sure the interlock wiring is as it 
> should be - and  Lou has given some pretty definite directions on that.
>
>  73
>
> Peter G3RZP
>
>
>
>
>
>  73
>
> Peter G3RZP
>
>
>
>
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