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VK2TV > TECH 10.06.05 20:29l 111 Lines 5944 Bytes #999 (0) @ WW
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Subj: Re: AC 3 Phase Power
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Sent: 050608/0914Z @:VK2TV.#MNC.NSW.AUS.OC #:15556 [Kempsey, QF68JX] $:100267VK
From: VK2TV@VK2TV.#MNC.NSW.AUS.OC
To : TECH@WW
Hi John, and others,
I've edited John's message in order to comment on points relevent to
Australia. The comments made are not intended to deride John's comments,
they are just to point out the differences that exist in my part of the
world.
G8MNY wrote:-
> The wire colour scheme may differ between countries & also the voltage!
In Australia we've had quite a variety of supply "standards" over the years.
In addition we've had to deal with a variety of colour standards, courtesy
of imported equipment and rules' changes.
The nominal supply voltage here is 240v, with a normal tolerance of +/-6%,
which gives a range of 228 to 254 volts. Even 240v can present problems for
some equipment designed for 230v and (somewhat unpopular) moves are afoot to
bring us into line with the Eueopean standard of 230v. At one time Western
Australia (or parts thereof) had a supply voltage of 260v. Even the
frequency of the supply has not always been 50Hz. Parts of Sydney were at
one time supplied from the railway's 25Hz supply, and before that the Sydney
CBD was supplied with 250v DC mains, and some of those old DC-days
switchboards still exist in older buildings. It's not much more than 50
years since the last DC mains were removed from Sydney. The place where I
served my apprenticeship in the early 1960's was supplied with a 250v
motor-generator set at about that time by the supply authority so that we
could still test DC motors after the DC supply was replaced with AC.
> NEW COLOUR HAZARDS !
> New EU colours are Brown Black Grey for Lives & Blue Neutral
> replace Red Yellow Blue for Lives & Black Neutral. Green/Yel earth.
The usual colours for the three phases in Australia used to be Red, Yellow &
Blue but when the Green/Yellow standard for earth wires was introduced the
use of Yellow as an active conductor was banned. It was replaced with White.
Having said that, the standards never specified what colours could be used
for active conductors (the neutral is deemed to be an active conductor),
with the exception of Green or Green/Yellow which was reserved for the
earthing conductors. Whilst R/Y(W)/B for three phase and R/Black for single
phase were the most common combinations, one could not count on this being
the case.
> N.B. the lethal change in use for both BLACK & BLUE colours!
Maybe the situation is different here but one never (or should never) take
colours for granted. One should always test for polarity.
In my forty years in the electrical trade, with twenty of those years being
an employee of an electricity supply authority, I only ever encountered one
case where the "wrong" colours were connected up. This was on a stove where
the connections were performed illegally by a painter. The stove was
connected over two phases but one of the two Red wires was the neutral, and
not an active. The black wire was the other active. The result was that some
elements heated up "real quick" as a result of having 440v applied.
> Single phase will change from Red live, Black Neutral to Brown & Blue
> respectifully. But highly confusing in a 3 phase board with both old black
> wire loads for Neutrals & Black Bus feed for live! Brown & Blue sleeves are to
> be used over Red & Black wires!
>
> I can see many 230V loads being tested on 400V & several deaths from this
> Red-Green blind safety change!
We adopted the Brown/Blue in lieu of Red/Black many years ago for cords but
cords of either standard are often encountered. So, too, are some
Black/White cords.
I am unaware of any fatalities arising out of the use of "different"
colours. I do know of two instances where 440v was applied to appliances.
One was the example above with the stove. This did not create a life
threatening situation. The worst result could have been a blown hotplate
element, simmerstat or fuse. The other case was a result of a negligent
linesman who swapped a phase and neutral in a two phase residence after some
mains augmentation (multicore overhead service conductor was not colour
coded). In this case an active was (effectively) connected to ground at the
comsumer's switchboard (most of Australia uses the Multiple Earthed Neutral
(MEN) system wherby the neutral is connected to earth at every consumers'
switchboard, as well as at the distribution transformer). This would have
created a voltage gradient around the earth stake at the house and,
depending on the value of resistance in the earth stake circuit, may have
left the switchboard surround and other earthed parts of the installation
alive at "some" voltage between 0 and 250v. In addition, some appliances had
440v applied and suffered damage from over voltage.
I don't know if this is the case in other countries but over here in rural
areas one often finds 240/480v mains. This arises from single phase
distribution transformers which have two secondary windings, the centre of
which is the neutral and the outer connections being the two phases which
are 180ø out of phase. Such an arrangement provided for spreading the 240v
load over two phases but it also provides 480 volts for such things as large
welders and pumps on farms. Given that a 5HP single phase motor requires
something of the order of 80A no-load starting (inrush) current, it makes a
lot of sense to run it off 480v if that supply voltage is available (and the
motor is wound for 480v, of course). In recent years there has been a
tendancy to move away from 480v rural supplies. The increased useage of
decent mains conductors, and more distribution transformers has reduced the
voltage drop problems that were prevalent when long runs (over half a mile)
of 7/.044 were common in rural areas. When I was the voltage investigation
officer (I investigated all manner of supply irregularities) for an
electricity supply authority, such runs were quite common.
Soapbox has been put away; goodnight.
Cheers ... Ray
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