🚀 go-pugleaf

On Nov 24, 10:58 am, "Phil Allison" <phi...@tpg.com.au> wrote:
> "Stupider than Anyone  Else"
>
> >I have to phases of power supply to my house - so three power lines, two
> >phases plus neutral.
>
> > I've on occasion wondered what would happen if we lost the neutral line.
> > It seems to me that we'd then have the voltage between the two phases
> > across two sets of appliances, one set attached to one phase, and the
> > other set attached to the other phase, with the two sets in series as a
> > result of their common connection to the neutral wire. Since the two sets
> > are unlikely to represent equal loads, the net result would be a large
> > overvoltage on one set of appliances.
>
> > My electrician says it's not an issue, but I can't see why.
>
> ** Loss of the neutral conductor in a 3 phase ( or 2 phase) AC supply system
> can easily be a DISASTROUS  event.
>
> For example:
>
> In the live entertainment productions -  high powered lighting and sound
> systems operate from 3 phase outlets via a hefty 5 pin plug and socket.  If,
> due to wear and tear or damage to the plug or socket, one of the phases
> drops out  -  that is an annoyance but not a disaster.
>
> However, if the pin carrying the neutral fails to connect or as is often the
> case *disconnects* during a show because of overheating   -  ALL HELL
> BREAKS  LOOSE !!
>
> Typically, some of the lamps will glow very brightly for a second or two and
> fail, then other previously dim lamps will follow suit.  The AC fuses in
> amplifiers will pop instantly and some equipment will be seriously damaged
> when the PSU sections are destroyed. It all happens in a few seconds, while
> the operators stand there with their mouths open  !!!
>
> The MEN system:
>
> In Australia, AC power delivery uses a system called " Multiple Earth
> Neutral "  -  which requires that the neutral conductors in a premises be
> connected to the plumbing system at the distribution board (ie power box).
> It also requires that an earth stake be installed for the same purpose, but
> some older premises may not have this.
>
> Because EVERY premises has MEN installed, the ground itself and underground
> metal plumbing act as an alternative neutral, should the supply conductor
> feeding a given premises fail. The disastrous event sometimes experienced in
> live entertainment systems is hardly possible in domestic or commercial
> premises.
>
> So the sparky is right.
>

The scenario you mention with live entertainment is particularly bad,
as when you think about it, unlike a fixed installation you can't bond
the earth and neutral in these portable 3 phase to 240v outlet mains
boxes.  If you did, it would trip any earth leakage breakers upstream
- if these are fitted.


To make matters worse, in live entertainment, the major loads are
almost all amplifiers, and lighting. None of these are stable loads
(amplifiers are changing their load current draw constantly with the
music and lights are being dimmed, flashed often in large groups. )


Therefore if the neutral lead fails, there is no bonding to earth to
back it up, unlike a residence, and with the inherent instabilty of
the load balance , massive damage is guaranteed.


> ....  Phil