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From: Robert M. Riches Jr. on 15 Oct 2007 21:45
On 2007-10-15, Unruh <unruh-spam(a)physics.ubc.ca> wrote:
> "Robert M. Riches Jr." <spamtrap42(a)verizon.net> writes:
>
>>On 2007-10-15, Unruh <unruh-spam(a)physics.ubc.ca> wrote:
>>> "Robert M. Riches Jr." <spamtrap42(a)verizon.net> writes:
>>>
>>>>On 2007-10-14, Unruh <unruh-spam(a)physics.ubc.ca> wrote:
>>>>> "Peter D." <psd(a)live.home.invalid> writes:
>>>>>
>>>>>>on Saturday 13 October 2007 10:13
>>>>>>in the Usenet newsgroup alt.os.linux.mandrake
>>>>>>Adam wrote:
>>>>>
>>>>>>> Peter D. wrote:
>>>>>
>>>>>>[snip]
>>>>>>> I don't know much about this and hope someone will correct me, but as I
>>>>>>> understand it, your typical American house has two 110-120V feeds out of
>>>>>>> phase. The entire house is wired for 120V (plug has vertical prongs
>>>>>>> plus ground pin). Somehow the two feeds are combined to get 220-240V
>>>>>>> (plug has horizontal prongs plus ground pin, or sometimes circular
>>>>>>> prongs), but that's only run to the few places where 240V appliances
>>>>>>> would be, typically the range (stove/oven), clothes dryer, and larger
>>>>>>> air conditioners.
>>>>>
>>>>>>I was assuming each house had a street supply of 220V and a transformer
>>>>>>with a single phase 110V output, but a two phase system could be used.
>>>>>>I am not the man to ask about US power supply techniques.
>>>>>
>>>>> Nope, each house gets 220 volts swinging in opposite phases WRT ground.
>>>>> Thus by using ground ( a big copper rod driven 6 ft into the ground) you
>>>>> get two 110 volt outputs. If something goes wrong with the ground, you get
>>>>> a 220 running through the two phased 110 circuits in series.
>>>
>>>>In all installations I have seen, the neutral has been
>>>>supported by a third wire from the transformer on the street
>>>>to the panel in the house. The ground rod does not normally
>>>>carry any substantial amount of current.
>>>
>>> You may be right. I would worry about the ground rod getting disconnected,
>>> which would be easy for some homeowner to do, not knowing what in the world
>>> it is for. I am pretty sure that the high voltage line into the street
>>> transformers does use the ground as a return, but could be wrong about that
>>> as well.
>
>>All the installations I have seen have had a metal wire for
>>return of even the high voltage (lower current) primary.
>
> In our area there is only one single high voltage wire. There are three
> things. There is the high voltage three phase which comes into the
> neighbourhood, which runs to a transformer which converts it to single
> phase. That is then fed to the transformers outside the house where it is
> converted to 2phase 110. As far as I can see there is no return wire on
> that single phase high voltage line.

I'd be _very_ surprised if there isn't a return wire hiding
somewhere. If not, I would recommend wearing rubber boots
when outdoors and/or keeping feet close together and never
lying down on the ground.

--
Robert Riches
spamtrap42(a)verizon.net
(Yes, that is one of my email addresses.)
From: David W. Hodgins on 16 Oct 2007 07:14
On Mon, 15 Oct 2007 20:26:24 -0400, Moe Trin <ibuprofin(a)painkiller.example.tld> wrote:

> Some communities require the utilities (electrical, phone, cable) to be
> underground. As such, the transformers are on concrete pads, often
> hidden by bushes. Generally, this is "newer" neighborhoods (ours is 18
> years old) in areas were weather MIGHT be a contributing factor (we
> get rather violent thunderstorms two/three times a year).

One of those "strange but true" shows, had stats on lightning strikes
for various electrical supply systems. Apparently, underground systems
are more likely to be damaged by lighting, than above ground. Seems
to defy common sense, but I have worked with one company, where the
underground backup transformer took a direct hit, blew up, knocked
out the concrete wall between it and the main transformer, knocking
it out too. About 50 ibm 3380 drives died over the next few months,
due to the damage caused by the instant power off. They were isolated
from the actual strike by a ups system, that, while it died (batteries
all blew up), did prevent the extra voltage from being passed on.

Regards, Dave Hodgins

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