On Sun, 17 Aug 2008 10:24:06 +0100, Mike Harrison
merida.demon.co.uk> wrote:
>According to my spies Sn!pe of (Sn!peCo World Wide Wading Birds) writes
>>Flash Gordon wrote:
>>
>>> Hello all, a bit off-topic, but I have a question about power in the USA...
>>>
>>> On of my brothers is moving to Silicon Valley (he has a 3 year work visa
>>> and his new company will sponsor him for a permanent work visa) and has
>>> a lot of expensive 220-240V Hi-Fi & AV equipment. One of his mates has
>>> said that houses often have 240V in the garage and kitchen. So what we
>>> want to know is whether the power is coming in to the house at 240V and
>>> then being stepped down so he would be OK running a 240V circuit to the
>>> lounge or whether it is stepped up for the garage making this a bad idea.
>>
>>Not that I have personal knowledge of this, but I was taught that they
>>have two phases, each 115V with respect to earth, so 230V between
>>phases.
>>
>A big problem would be that USA electrickery is 60Hz frequency while UK
>electrickery is 50Hz. If the equipment works at all, things with motors,
>such as cassette decks, turntables may well run fast. Things with
>screens may not produce a stable image. Tuners etc. may not sync to
>broadcast signals.
Erm ... no.
I have a book somewhere in the archives which actually states that TV
frame rate is locked to mains frequency, and maybe that was a plan
once, but it's not true!
In the old days, turntables used to work with shaded-pole induction
motors, which were largely affected by mains frequency. Some of the
cleverer turntables had an adjuster, and you could use strobe discs to
help to set the speed. These relied on the fact that the light output
from lightbulbs is not constant, and varies in proportion with the
mains frequency, but that's another story.
The CEGB takes great pains to prevent the frequency from straying far
from 50Hz.
When I worked at the BBC, there was a huge meter in the Central
Appartus Room which showed the frequency of the incoming mains. I
never saw the needle more than a pointer's width away from 50Hz.
There was also a much smaller digital meter which always read 709379.
That was a bit more critical :-)
Modern AV kit usually has switched-mode power supplies which will work
with supplies from 90 Volts to 250 Volts AC or DC.
Cassette decks and turntables will have DC motors, and the mains
frequency will not affect them.
Older equipment may use traditional power supplies using transformers
followed by bridge rectifiers. This can be a problem if the mains
supply is low.
I'd be surprised if any expensive equipment using this type of supply
didn't have a means of changing the tap on the power transformer
unless it's more than 20 years old!
The nominal voltage for a single-phase mains supply in the USA used to
be 117 Volts - this being the lowest voltage which could possibly be
lethal. Have you seen that James Bond film were somebody is
electrocuted in a bath because a hairdyer is thrown into it? Bah!
I think that the nominal voltage has been reduced to 110 Volts.
For higher power appliances such as electric ovens and washing
machines, I think that they use two or three phases.
The voltage between two phases of 117 Volts would be about 200 Volts,
but I don't expect that you'll find an outlet for that which you can
use easily.
--
Humbug
