[Amps] Electrical Distribution Methods

[Paul Christensen]

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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