Everybody knows that (1) telephone service is usually not interrupted when electric power goes out and that (2) you can talk on the phone while soaking in the bathtub without electrocuting yourself. Why? What's so special about the way telephones are powered?
Instead of being wired to your house electrical line, most telephones are powered by storage batteries located at the telephone company’s central headquarters. The storage batteries, of course, are themselves charged by the local electric company line, but when possible, the phone company, in its infinite wisdom, tries to connect to two different power sources–in case the generator supplying one line goes out, they can fall back on the other. If everything fails, the batteries can usually supply enough current to cover short breaks in service. Should there be a longer interruption, many of the central stations are equipped with diesel generators that can be pressed into action with a flick of the switch.
All of this complicated re-routing of electricity is made necessary by the happy fact that the telephone runs on a much smaller current than that supplied to homes by the power company–a happy fact because that’s what keeps you from roasting your eyebrows when you’re phoning from the tub. It takes a mere 100 milliamps of current flowing through your bod to bring on a killer dose of “ventricular fibrillation,” as they call it in the trade. Your heart stops beating and starts to quiver like an emotionally distressed bowl of Jell-O, cutting off the flow of blood to the brain and other vital organs. The electrical outlets in your home pack a whopping 15 amps; your humble telephone carries less than a tenth of a milliamp. That isn’t much, but under some circumstances it might be enough to do a little damage, so underwater telephony should still be approached with caution. No deaths have ever been reported from this sort of thing, but there’s a first time for everything.
Send questions to Cecil via firstname.lastname@example.org.