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Of Dogs and Toilets: The Law of Unintended Consequences

August 29, 2012 - 0 Comments

By Steven Shepard, Contributing Columnist

Wikipedia defines it as “A perverse effect contrary to what was originally intended.” It turns out that the law of unintended consequences is alive and well, and has been for years in the world of telecommunications.

Consider the story of the woman who called the telephone company back in the 1940s to report a problem. The problem, it seemed, was that every time the phone rang, her dog shrieked and barked and did the canine equivalent of St. Vitus’ dance.

Literally, the Well Grounded Pet

Humoring her, the phone company sent a technician out to look at the phone — and the dog. What he found was funny, and quite a relief for the dog.

It turns out that the woman lived in a rural area, far from the nearest central office. To deliver service to such far-flung places requires miles of expensive wire, particularly since each phone requires a pair of wires. But a clever engineer in the early telephone company determined that it was possible to deliver phone service with a single wire.

The trick was to use what is called a ground return, which simply means that the earth is used as the second conductor to complete the circuit back to the central office.

In practice, it was a simple technique (and still very much in use today). The phone company ran a single wire to the house, and then drove a long copper pipe into the ground, to which the technician connected the other lead of the phone, completing the circuit.

But this is where things get a little jolting — for the dog. The ringing current that gets delivered to the phone is about 90 volts AC. If the dog is wearing a chain collar, and the chain collar is connected to a long chain, and the chain, in turn, is connected to the copper pipe to prevent the dog from wandering…

Why Plastic is Such a Good Insulator

Here’s another story from the journal of unintended consequences. “My phone quit working a few weeks ago, but every once in a while, when I flush the toilet, it rings,” said the woman to the technician. This was one for the books.

After crawling all around the toilet in her bathroom (she lived in an old Vermont farmhouse that was quite small; there was only one bathroom), he figured out the relationship between the ringing telephone and the flushing toilet.

Like the woman with the barking dog, she too had a single conductor, ground-return connection for her phone. Years before, when the phone was installed, the original technician attached the ground return wire to the copper cold water pipe that fed water to her toilet.

A few weeks before, the pipe, now well over a hundred years old, corroded through, and the plumber replaced the corroded section of it with — you guessed it — a nice, bright, shiny piece of PVC. The plastic section acted as an electrical insulator, preventing the phone from ringing — unless, of course, there happened to be water flowing through the pipe at the exact moment the phone decided to ring.

I love this industry.

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