Re: Physically Protecting The Local Loop Metwork?

Today customers own all their equipment that is supposed to be
> certified. But what happens if the customer alters the equipment or > it is defective? What happens if a high voltage is sent out > accidently over a telephone line (ie house current, either 110 or > 220, or ringing current meant for an extension telephone of a PBX)?

In the United States, customers are not supposed to connect anything to the Public Switched Telephone Network unless it conforms to FCC Part 68 (see

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for details). This is supposed to guarantee that the device does not create problems for the network or other customers on it.

So what happens if you ignore that, and attach house current to the phone line? This would likely blow a fuse somewhere. If not, the alternative would be for the phone wires to catch/start a fire, as they usually aren't of a sufficient gauge for that kind of current.

If you were to connect something that didn't blow a fuse but caused problems for other subscribers, they could file a formal complaint with the FCC against you, assuming they could figure out who you were.

I think I remember once seeing a little circuit board that did nothing except guarantee Part 68 compliance. (It even had its own Ringer Equivalence Number, a whole 0.0B.) It was designed for people who wanted to attach their own homebrew projects to the phone line but not worry about causing problems. I don't remember where I saw it, sorry, but you could probably find something like it wherever you buy other bare electronic circuit thingies.

John C. Fowler, snipped-for-privacy@yahoo.com