Corroded Copper Stops Dial Tone

A few decades ago, I owned a home in one of Boston's western suburbs. The house had been built during World War II, when nobody with any business building houses was doing so. But that's another story. This one is about the telephone.

One day, I picked up the phone, and there was no dial tone. I went to the neighbor's house (this was before cellphones) and called the phone company to report the problem. The company said it would look into it, so I returned home. A little while later, the phone rang -- it was the phone company asking about the problem. I hung up, checked for a dial tone, and called back to report it was A-OK.

All was fine for a few days, but then the problem came back. I walked over to the neighbor's house, and this time I called my house. My wife answered, and the phone seemed OK.

This went on for a while. I kept reporting the problem, and the phone company kept avoiding it. Eventually, I discovered that, when there was no dial tone, I could fix the problem by waiting for an incoming call or by calling my phone from another one.

This got tiring, so I kept calling and explaining the problem in more detail. Service calls were made, but there was never a diagnosis. Eventually, a young guy in a Harvard T-shirt came out in a bucket truck. I explained the problem to him in great detail, and he said he would work on it. I looked out every once in a while and saw his bucket truck moving from pole to pole. This took the better part of a morning, but I was pleased that someone was trying to fix the problem.

Eventually, he came back with a big smile. "I found it," he said. He showed me a wire splice that he had cut apart. It was a plastic sleeve with a metal crimp device in it that was used by the phone company techs to connect phone wires. It had a lot of green corroded copper salts inside. He said that when it rained or was humid, the copper corroded, and eventually the wires lost electrical contact. The telephone system works on two voltages -- a lower voltage for the dial tone and a higher voltage for the ring -- and there's the answer. When the higher voltage was applied to the corroded connection by calling (ringing) my phone, it broke through the corrosion and re-established the connection (imagine a spark welding the wires back together). This would last a while, but eventually the tiny connection would corrode again.

The Harvard man replaced the splice with a new silicone-filled one, and that solved the problem. I never had a dead line again.

Dave Boccuti is a mechanical design engineer with more than 30 years of experience in a number of different industries, including consumer products, medical devices, and custom automation equipment. He is developing disposable diagnostic medical devices at Daktari Diagnostics in Cambridge, Mass.

Tell us your experience in solving a knotty engineering problem. Send stories to Lauren Muskett for Sherlock Ohms.

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