ECN Forum Forums General Topics of the Trade General Discussion Area Can you be electrocuted while on the phone in the bathtub?

once on a construction site the phone was down and it was raining when i found the break in the wire and went to re-splice it i found out about ring voltage: ouch!

Use a wireless phone. anyone should stand 3V

As to the voltage on phone lines, "nowadays" I think the voltage is even higher for digital lines (T1, DSL).

I've always heard that one should not use a sink or tub or shower during a lightning storm and to stay away from windows...

I do remember once during a storm there was a very bright flash of lightning outside. The phones briefly "chirped" and a light bulb in a lamp suddenly blew out (everything else was OK). That was a bit startling...

I've seen phone stuff blown by lightning twice. Once it was a big fancy phone and once a PABX. Both had huge black spots on the circuit board. pretty impressing.

The weirdest experience I had with lightning was in rural Italy. There was a real bad lightning storm and we were sitting inside. Suddenly I saw sparks flying from one hole of the receptacle to the other! Only lasted for an instant, then it was gone. Some electronics that had been plugged in were shot.

Per TIA/EIA/IS-968 section 4.4.4.2 (formerly FCC part 68) and UL60950/UL1950 (annex M), ring signals shall be less than 300v P-P, or 200 Vp to ground, across a termination of at least 1 megaohm. Of course that defines the high end you need to design to, not the norm. The NRTL's I have worked with use 125 Vp or 150 Vp when deciding how much spacing should be between a POTS line (TNV3) and other circuits.

i don,t know if your phone can hurt yoy,but just look at your bill every month,now thats a shock.

In the "old" days in Britain, the line came straight off the exchange batteries which were held at a nominal 50V DC. These days, it seems that the modern digital exchanges regulate it down from a slightly higher voltage. When a linecard goes bad (as seems to happen quite regularly in my local CO -- so much for modern reliability!) the voltage goes up to a little over 60V.

By the way, test voltages which exceed the usual nominal can also be applied to the line during routine tests as well.

You gotta stop calling all those 900 numbers!


[This message has been edited by pauluk (edited 06-01-2004).]

As to the voltage on phone lines, "nowadays" I think the voltage is even higher for digital lines (T1, DSL).

No. T1's can power the terminal unit at the customer premises but it is still 48vdc. DSL is just piggy backed on a POTS line and so there would not be a difference.

Talking about lightning, we are primarily a telecom company and whenever we install a new key system or PBX we always provide secondary protectors on all CO lines. Secondary means after the TELCO provided protectors. As I mentioned earlier, most TELCO protectors will limit surge voltages above 300 volts, usually 400 to 600 depending on what they have on the truck that day. Our secondary protectors will clamp at 235 volts with a 150ma fuse that will open both sides of the line when it does. I can say that we have never lost a piece of equipment this way. We have lost plenty of protectors though.

One extreme case that comes to mind was an installation in a house for a home based business. This was in a rural area and every time there was a lightning storm the protectors would literally be blown across the basement. We would come pull out what was left and plug new ones in and they would be good until the next storm. We notified the TELCO because this should not be happening if their grounding and protectors were doing their job. Even though each time they lost their alarm system and other electronics but not the telephone system, this was our fault and they refused to pay for the service call. Can't win!

-Hal

hbiss, don't mix up yer DSLs! Residential ADSL is just POTS plus high frequency DSL, with the only hazard, under normal conditions, being ring voltage. But HDSL, HDSL2, and HDSL4 (all 1.544 Mb/s, like T1) are powered at -190 VDC constant. These will whack you pretty good - expletives and everything. A T1 remote unit when "line powered" and funtioning normally will usually not have any hazardous voltages present - not because the CO isn't generating hazardous voltages, but because it is a constant current system. The CO end will output whatever voltage it needs to, up to -140 VDC, or + and - 140 VDC depending on its settings, in order to drive 60 mA through the loop. The device at the end of the loop MAY (sometimes may not!) have < 50 VDC across it ,measured tip and ring to tip1 and ring1, but the repeaters along the way may have up to the max voltage to ground. Break the loop, or remove the remote unit, and one pair goes to the max output of the CO unit. "Locally powered" T1 systems not using line or span power will only have about a 3 Vrms signal present.

electech:

That's exactly what I was gonna say