What gives a telephone power? Why can I use it when there is no electrical power? Do all phones work when the power is down?
The telephone company delivers low-voltage (well, lower than mains) power down the phone lines; any phone that can work on this alone will continue working if your ordinary mains electricity is cut off, I suppose it’s possible that a very widespread power cut could knock out the phone company too, but maybe they have emergency generators.
Phones that require additional power (from a mains outlet) - usually cordless ones, will usually cease to function when there is a power cut, unless they have backup batteries.
Power on the phone lines is provided to the phone company at their switching gear. It is usually low voltage DC power with on-line battery back-up (UPS-like).
You couldn’t use it in any significant amount even if you did transform it up to house voltages and invert it (make it AC) because (a) the wires are too small to carry a significant amount of power and (b) they have circuit breakers / fuses on the other end to prevent accidental fires or electricutions.
Get your own battery back-up (UPS) and generator if you need them. The UPS will carry you through brief interuptions and a small generator ( 2000 VA ) could handle longer outages.
- Standard telephones are powered by 48 Volts DC on the phone line.
- Phone company switching office run almost entirely on DC (batteries).
- These batteries are charged by incoming power from the local electric utility company.
- These batteries can run the phone network for hours if not days.
- switching office also have backup generators for the event that commerical power is going to be down for extended periods.
Disclaimer: Some of this may be somewhat out of date as I haven’t been in a switching office in several years. But that is how it used to be done (In a GTE switching office at least).
Also the long run (from the telco central office to your house)on small wires prevent you from pulling any significant amount of power over them.
When Verizon lost commercial power to the central office at 140 west street in Manhattan last September 11th, generators ran for about 8 hours until their supply of diesel fuel was exhausted. Battery reserves lasted for perhaps four hours after that.
I have noticed that the cordless ones in shops have a little sticker on that says something to the effect of “not to be relied upon in an emergency”.(Put there by company lawers no doubt)
I guess if your house is ablaze and the mains powers gone a cordless radio system will stop working.
Cecil covers some of these questions in Can you be electrocuted while on the phone in the bathtub?
The official name for this is " central battery system ". In the very early day of the telephone ,each instrument had its own battery located at the subscribers home. Not very efficient hence the change to the present set-up
There is an important distinction to be made, though. Talking over a telephone requires a very small amount of voltage but making a telephone ring requires about 90 volts AC. Old-style army field telephones could operate on 2 D-cells, but to make the other guy’s phone ring required you to crank a small generator (the same type of crank-generator one sees on really old phones).
In addition to generating ringer voltage, the army TA-43 field telephone has been an interrogation mainstay for decades. I doubt it could kill a person, but it’s certainly uncomfortable.
Personal Experience: Certain types of multi-line office phones will have one central unit that plugs into the wall outlet. Cut the power to this phone, and the rest of the phones on the system become inoperable
I can attest to that.
I once was adding phone jacks in my apartment. As I was working in the living room, I cut the main wires to strip them and attached them to a jack. As soon as I did, my roommate yelled that I had just cut off his call to his girlfriend. Hurrying to reconnect the two lovebirds, I began to strip the wires with my front teeth. I felt the slight buzz from the 2V potential of the live wires, but thought nothing of it. But I did think quite a bit about the 90V + accompanying current when his girlfriend called back! :eek: :eek: :eek:
The same thing happened to me when I was installing a new jack and a friend called, but I only got zapped in the fingers.
Stripping phone wire with my teeth is just kinda… what the hell were you thinking?
During the great ice storm of 1998, power up here was knocked out from anywhere from a couple of days on the Island of Montreal, to a few weeks on the South Shore. I can’t speak for the South Shore, but my power was out for three or four days, and the phones were still working.
However, since I have to plug in my phone (for call display, the flashing message waiting light, etc.), these features didn’t work, and the ringer was different - it was more high-picthed, like some generic backup ring.
Guess I wasn’t, Mom.
I can do it with my fingernails, but it bugs the @!#?@! out of me, a la fingernails on a chalkboard. Plus, the gap at the end of my two front teeth is the perfect width for phone gauge wire.
Y’know there are these wonderful little pliers-like devices that can strip wire neatly, without all the filling-rattling jolts a tooth-stripper is subject to.
At the very least, please don’t tooth-strip any kind of wire that is actually hooked up to anything.