Thanks Jim, that clarifies a little.
Sounds like you are saying that you have two 120v "legs" from the same
phase. That makes sense - mixing phases is not pleasant if you don't know
what you are doing.
However, it sounds like the two 120v legs are 180 degrees out of phase ?
That way, measuring between the two "hot" legs would give 240v ?
Over here, we have 240v between what we call "Live" and "Neutral". If I
measured between the "Live" legs of two 240v supplies on the same phase, I'd
get 0v ... right ? (Never tried it, I must admit - most of my EE is at 50v
or below, and mainly DC).
Just interested, that's all. I understand what we get over here (at least,
I thought I did). Not sure I get what happens "over there". Think I need
to go and read some more. Maybe it's just a case of terminology.
Thanks,
Jon
-----Original Message-----
From: Jim Nichols [mailto:jhnichols@xxxxxxxxxxxxx]
Sent: 25 February 2010 23:43
To: Olympus Camera Discussion
Subject: Re: [OM] Purchase of new camera case successful
Jon,
Though I'm not a EE, I can give you some general concepts of power
distribution in the US.
I live on a corner lot, alongside a fairly busy throughfare. There is a
3-phase distribution line along that street. Feeding our homes are a
connection to a single phase of that line, and the common neutral. These go
to a distribution transformer which supplies three or four homes. I have
little knowledge of what takes place in the transformer, but the output to
each home is made up of two 120 volt legs and a neutral. These feed the
breaker box busses. 120 volt branches are connected between either of the
two hot legs and the neutral. 240 volt circuits connect between the two hot
legs. Perhaps someone else can elaborate what happens in the local
transformer. I suspect that the transformer drops the voltage down to 120
volts and feeds two separate secondary windings, which are then fed to the
house breaker panel, along with the neutral.
Very few homes are served with 3-phase power feeds.
Hope this helps.
Jim Nichols
Tullahoma, TN USA
----- Original Message -----
From: "Jon Mitchell" <olympus@xxxxxxxxxxxxxx>
To: "'Olympus Camera Discussion'" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Thursday, February 25, 2010 5:25 PM
Subject: Re: [OM] Purchase of new camera case successful
> Hi,
>
> Apologies for answering my own questions. Not such an "American" trait in
> broadcasting any more though - it's spreading fast. Not that that's an
> excuse ....
>
> Not sure about moving supplier though. They all get the power from the
> same
> place. I think of it as a wholesale arm of the National Grid selling the
> power to any of the retailers (they are bound, I believe, to give them all
> the same deal). The retailers then sell it on to you. That's progress
> for
> you !
>
> Now on to a more interesting question for other members of the list (which
> I
> won't answer myself .... 'cos I can't !). There's a lot of talk about
> different power "legs" and "phases" to the same house from our US friends
> here. I have little idea how the power supply works in the USA (other
> than
> it is 110v 60Hz AC), but is the implication that you have more than 1
> phase
> in your homes ? Over here you can get either a single-phase supply or a
> 3-phase supply. Very few (if any ?) homes have a 3-phase supply, as these
> are intended for industry.
>
> Are your houses wired with some sockets on one phase and some sockets on
> another ? Doesn't this pose problems ? What if you connected 2 devices
> to
> 2 separate sockets that were on 2 separate phases - and then connected the
> devices together (VCR to TV via a SCART, for example). At best, nasty
> interference. At worst CABOOM, no ?
>
> And what about balancing the phases ? When I've played with 3-phase
> supplies (lighting rigs, for example) a lot of care is taken to ensure
> that
> the phases are fairly evenly balanced (approx same load on each phase).
> How
> do you do that within the home, when most home-owners don't understand
> this
> stuff ?
>
> I'm not questioning whether it is right or wrong, better or worse, but am
> interested in how it is done elsewhere.
>
> Oh, and most scary thing seen whilst working with 3-phase ? A colleague
> ran
> a long run of pre-terminated 3-phase power cable (120Amp, or thereabouts)
> over the roof of a stadium. He realised afterwards that he had run it the
> wrong way around (male & female connectors at wrong ends for the required
> usage). Whilst I agree it would have been a lot of work to de-rig and
> re-rig the cable, I am sure that it would have been easier (and safer) to
> chop the ends off and remake them the right way round rather than make 2x
> 3-phase Gender-Bender cables ! That was one VERY scary cable.
>
> Second most scary 3-phase incident ? The 3-Phase A0 photocopier we had at
> work until a couple of years ago. I still can't comprehend why you'd need
> 3-phase power for a photocopier !
>
> Anyway, this is all wildly off-topic (though fun).
>
> Jon
>
>
> -----Original Message-----
> From: Chris Barker [mailto:ftog@xxxxxxxxxxxxxx]
> Sent: 25 February 2010 21:48
> To: Olympus Camera Discussion
> Subject: Re: [OM] Purchase of new camera case successful
>
> Thanks for that Jon. But there is something you can do about it: move
> supplier, complain to your current supplier, to Ofgen etc ...
>
> And, don't you start sounding like an American broadcaster, asking your
> own
> questions ....
>
> ... or Conservative MP :-)
>
> Chris
> On 25 Feb 2010, at 20:26, Jon Mitchell wrote:
>
>> FWIW, we looked into this at work recently - problems at some of our
>> sites
>> with very low voltage. UK spec was changed recently to harmonise across
>> Europe. I don't have the exact figures to hand, but it used to be
> something
>> like 220v in Europe and 240v in UK. Now it is 230v in UK and the rest of
>> Europe. How did they get away without changing all of the National Grid,
>> substations, etc. ? They fudged the error-factor so now UK is something
>> like 230v +15%/-6% and rest of Europe is something like 230v +6%/-15%.
>> Phase is much more accurately defined, and has a far smaller margin
>> before
>> it becomes "out of spec" - but that was always the same across UK &
>> Europe
>> anyway. In reality, nothing has changed in the power supplied either in
> UK
>> or rest of Europe, but now manufacturers have to cope with a wider
>> voltage
>> range if they want to sell products across Europe.
>>
>> Anyway, back to the point, yes - in theory the power companies are
> required
>> to maintain a consistent voltage (within an alarmingly wide margin of
>> error). In practise, however, they regularly do not maintain this.
>> Especially in more rural areas. But who can do anything about it ? As
>> someone else said here - the general attitude of the power companies is
> "you
>> get what you're given".
>>
>> Does it suck ? Yes. Does it bother me ? A little. I know a couple of
>> SERIOUS hi-fi nuts who have taken matters into their own hands and
> installed
>> some serious power-conditioning units (basically, AC-DC-AC conversion)
>> and
>> run a separate ring-main just for their hi-fi components. Can I hear a
>> difference ? Well, yes - but more to the point is that the cost of the
>> hi-fi kit in question means it is worth a sizeable investment in power
>> conditioning to stop it going boom when the power drops (or rises) out of
>> spec.
>>
>> Gosh. 2 topics in a week that I can reply to with some experience !
>> What
>> is this list coming to ... ;-)
>
> --
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