[IP] more on Is broadband set to make power lines sing? - already does in the UK
Delivered-To: dfarber+@xxxxxxxxxxxxxxxxxx
Date: Wed, 25 Feb 2004 07:51:37 -0500
From: "Steven M. Bellovin" <smb@xxxxxxxxxxxxxxxx>
Subject: Re: [IP] more on Is broadband set to make power lines sing? - already
does in the UK
To: dave@xxxxxxxxxx
Andrew Bale says "while the UK trials below are clearly working, that
does not imply that they are demonstrating a good commercial model."
There's a technical difference (and often a sociological difference)
between the U.S. and Europe that has a big commercial effect.
The technical issue is line voltage: the U.S. uses 120 volts, while
Europe (and much of the rest of the world) uses 220-240 volts.
Delivering the same amount of power at 120 volts as at 240 volts
requires twice the current, which increases the resistance loss in the
wiring by a factor of four. As a result, U.S. power companies tend to
serve fewer houses per step-down transformer, since they don't want long
wire runs at 120V.
Beyond that, the average housing density is often greater in Europe
(except, of course, in big cities in either place); again, this affects
the number of transformers needed. The net result, if I recall
correctly some figures I saw around 1997 (when this idea first came
up), is that the average step-down transformer in the U.S. serves four
or five customers, while in Europe it servers about 100. This makes a
very big difference in the economic viability broadband over power
lines.
--Steve Bellovin, http://www.research.att.com/~smb
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