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'[EE]: Electrical mains distribution transformer 's'
2002\11\01@211303 by Jim

One last tid-bit seemed applicable from the chapter on
"Transmission and Distribution Systems", Pg 1061:

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189. Grounded secondaries.

To protect life and property in case a primary circuit becomes crossed with
a secondary, it is very important that the secondary be grounded. This is
preferably done by connecting the secondary circuit to water pipes where
these are accessible. Where the ground must be made outdoors, the most
practicable method is to drive a galvanized iron pipe into the ground to a
depth of about 8 ft. The points to be grounded in various kinds of secondary
mains are indicated in Fig. 52.

190. The grounding of secondaries up to 150 volts has been re-quired by the
National Electrical Code since 1913.

There is some doubt as to the advisability of grounding secondaries when the
difference of potential between any wire and ground is higher than 250
volts, owing to the possibility that shocks from such a system may prove

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Primaries crossing with secondaries continues even to this
day -

- I recall an article in PC Magazine (I think it was) where
one of the authors suffered utter destruction of most of the
operating-at-the-time appliances (including his PC).

It was attributed to a 'power distribution transformer primary-secondary
shorting event' ...

RF Jim

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2002\11\02@102831 by Alan B. Pearce

face picon face
>It was attributed to a 'power distribution transformer
>primary-secondary shorting event' ...

I wonder what the cause of the event was :)

A colleague who had worked at a power company in NZ told us of an incident
he came across where an opossum had managed to bridge the 400V distribution
voltage to the local 230V secondary side. Said animal took one last nose
dive into the bushes never to stir until found by the supply company

The problem it caused though was in a local chicken farm. It had outfitted
the rearing sheds with high efficiency bulbs with electronic ballasts for
best power consumption. The high voltage spike from the flash over through
the animal blew a low ohms protection resistor on the input in each of these
bulbs. This caused panic among the chickens which resulted in many dead

Apparently they replaced these resistors and the bulbs then worked again

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