Thanks so much for the interesting post. I was aware of the "ring main"
concept from the UK--in fact, the main power distribution on the
original 1930s Queen Mary is a ring main, at least according to an
engineering journal reprint I have featuring that classic ship.
As to z.f. or DC distribution. At the time I left New York City in 1981,
the mid-town Manhattan area including the theatre district had separate
DC distribution still running. At St. Thomas Church on the NW corner of
5th Avenue and 53rd Street, at least the organ blower and I think some
of the original (from the 1915 era) air handling motors ran off DC. I
believe this at one point came from the McKim-Mead-White designed IRT
(subway) powerhouse between 58th and 59th Streets and 11th and 12th
Avenues. For many years, I recall passing buildings that housed rotary
converters that provided the power needed by the subways from the 60 Hz
mains. I believe St. Thomas was forced to deal with the abandonment of
the DC distribution a few years later.
I believe at least some of the Broadway theatres ran stage lighting on
DC with resistance dimmers until the end of DC.
My wife's family home has a disused 25 Hz furnace control accessory
(don't recall precisely what) which must have been replaced when the
conversion was made here in the Greater Toronto Area to 60 Hz. It was
only fairly recently, i.e. in the 1950s or later.
I was interested in Tom's photo to see the 10 A "MiniBreaker" as a
normal 14 gauge wire is rated at 15 A, and that is the standard size for
a house branch circuit in the U.S. and Canada. Within the last 30 years
or so, multiple-outlet circuits rated at 20 A have been permitted (only
more recently in Canada). Those have to be wired with 12 gauge wire.
Another interesting system is the "Multiple Earthed Neutrals" where the
neutral and earth are connected together at more than one point in
Australian and New Zealand systems as I understand it.
On 2012-01-16 10:09 AM, George Brock-Nannestad wrote:
> From: Patent Tactics, George Brock-Nannestad
> Hi Richard,
> just a few comments on power supply and mains. In Denmark, the foremost
> source for amplifiers were batteries for High Tension and accumulators for
> the cathodes. So-called "battery eliminators", i.e. mains supply converted to
> suitable z.f. voltages, were an important item, and actually the major
> selling product of Bang& Olufsen when they were founded. Note my use of z.f.
> (zero frequency) for DC; it was to honour M.G. Scroggie of wireless fame who
> used this term because he thought that DC voltage was an abomination.
> Danish mains was DC (back to normal, again) for many years in many parts of
> the country, and the last place to give in to AC was Copenhagen; it only
> happened in the early 1960s. Gramophones had universal motors (some neat
> little things, but very good).
> Fuses and switches for DC have to have a much sturdier construction than for
> AC, because you really have to break an arc, whereas in AC there are two zero
> crossings of the current per cycle. This means that you do not need nearly as
> much cooling of the ionized gases to prevent re-ignition when the voltage
> goes up again. In the US, using 110 V for housing, the fuses and switches
> again have to be sturdier because the amperage rating is higher.
> In the UK, things are very interesting indeed. They do not have main circuit
> breaker fuses but fused outlets, or rather fuses in the plugs. And very many
> use ring mains, i.e. the circuit through the house has two parallel circuits
> going round and back to the main switch. This very much reduces the voltage
> drop on the in-house distribution. This is in sharp contrast to the star
> system used in Denmark, but I suppose you need it because the "normal" plug
> for kettles and the like has a built-in 13 A fuse, and you can have both your
> kettle and a toaster on at the same time. Not so in Denmark, you are limited
> to 10 A. A normal fuse has a time function that makes it blow instantly at
> 1.5 times the rating, and I suppose in one hour at 1.1 times the rating - I
> haven't checked since 1970.
> All the things you did not want to know about mains! And we have not even
> started on 3-phase.
> But Tom's photographs are beautiful!
> Best wishes,
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Quality tape transfers -- even from hard-to-play tapes.