12v shock! - Electrician Talk - Professional Electrical Contractors Forum

Mike Guile · 02-07-2010, 10:21 AM

Sort of funny story. I was down in a muddy wet water filled ditch a few years ago next to a pool. The pool guy cut the phone lines going to the barn. I get down there to see what we need to do to splice and rebury. I got a nice little jolt. Basically, about the same as 120V zap. The guys I was working with at time laughed and said you can't get hurt from 12V. I didn't know or care at the time it was live and it was carrying 12V. Well, I was googling body resistance this morning for some reason and calculated it all out. Thanks to Ohm's Law, it confirms I was getting zapped and could have been lethal according to numbers. Nice article for those interested

http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

Chris Kennedy · 02-07-2010, 10:33 AM

Where did you get 12V from? It is my understanding phone lines can have up to 100V dc on them.

JTMEYER · 02-07-2010, 10:39 AM

I was always told ring voltage was 90vdc, and yes it WILL give you a hell of a jolt. If you get "called" you will remember it. Also I have been hit with 12vdc from a car battery. It feels kinda like a bug bite. Now my mother had a Delta 88 deisel back in the 80's, one of the battery connections had a habit of working loose, so she caarried a little 8mm wrench to tighten it up with. One day she came home with a blister around her ring finger, and her wedding ring in her pocket. She had shorted her ring between the positive cable, and the car body. I guess it got real hot, real fast.

Mike Guile · 02-07-2010, 10:41 AM

not sure which wire. The wires were cut by bulldozer excavating the pool halfway between house and barn. There were 2 bundles of gray insulated wires. Each bundle had 10-15 x 24 gauge or so in each. It was a long time ago and I don't remember much other than I got zapped good and we just respliced the 2 wires needed to get phone line working in barn. It was hooked up to a 12 or 16 V transformer in house I think?

**480sparky** · 02-07-2010, 10:43 AM

Quote:

Originally Posted by JTMEYER

I was always told ring voltage was 90vdc, and yes it WILL give you a hell of a jolt. If you get "called" you will remember it. ..........

I think you're correct 90vdc is the 'ring' voltage.

Thayer · 02-07-2010, 10:45 AM

Sounds like you just happened to touch the exposed conductor when they received a phone call. Its 90 VDC from the phone company, so you will feel it.

Mike Guile · 02-07-2010, 10:47 AM

Damn, this job was like 7 or 10 years ago. It definately was a phone line , I vaguely remember a 45-50 volt reading somewhere as well, but AC??

My memory is getting real bad, sorry. Could there have been a voltage drop to 50V AC at 125 out ?? I don't ever remember using my meters for DC ever, except working on car maybe.

Mike Guile · 02-07-2010, 10:48 AM

sorry..125 ft from the house to the cut conductors

mattsilkwood · 02-07-2010, 10:57 AM

If the conditions are right you can feel the operating voltage, I was knelt down on the wet ground one time making up a tap box and I could feel it going through my knees. it didn't hurt, just a slight tingle. I have been called before as well and that will wake you up.

jw0445 · 02-07-2010, 02:35 PM

Thayer is correct. Ringing voltage is 90-100 volts AC depending how far away from the phone company equipment you are. POTS (plain old telephone service) voltage is neg. 52 volts DC. Ringing voltage will definitely make you jump if your holding on.

waco · 02-07-2010, 02:40 PM

Ring voltage will get your attention, but, in my opinion, skin resistance is too high for 12 volts to do much if anything. Working around dashboards and batteries with rings on is a good way lose a finger.

Shado · 02-07-2010, 06:44 PM

Quote:

Originally Posted by waco

Ring voltage will get your attention, but, in my opinion, skin resistance is too high for 12 volts to do much if anything. Working around dashboards and batteries with rings on is a good way lose a finger.

But my wedding band will not come off anymore boss....I have to tape it up nowadays.....

Electric Bill · 02-07-2010, 07:53 PM

Telephones lines should have 48vdc on them then 90-100vdc for ringers

B4T · 02-07-2010, 08:07 PM

Pretty sure it's 48V DC....

waco · 02-08-2010, 07:53 AM

Quote:

Originally Posted by Shado

But my wedding band will not come off anymore boss....I have to tape it up nowadays.....

I appreciate the problem. I had to have mine cut off because of a bee sting, but I wasn't working under dashboards. Used to be, no jewelry of any kind when working with electricity. If your work around battery voltage, I think you need to shuck the ring.

Marshall175 · 02-08-2010, 09:24 AM

so does anybody know for sure whether it is ac or dc?

crazymurph · 02-08-2010, 10:21 AM

Quote:

Originally Posted by Marshall175

so does anybody know for sure whether it is ac or dc?

It is DC. I have been in the rooms where Rochester Telephone ( now Frontier) keep the batteries. The batteries look like carboys and they have several in series and parallel. They are tied together with 750 kcmil and tie to copper bus that is 5000 amp. The system is -48 VDC and the ring is 90 VDC.

Fairley · 02-08-2010, 11:03 AM

Its DC 48V. Sure!

Thayer · 02-08-2010, 11:38 AM

You gentlemen are correct. It is DC, I simply wrote AC out of habit.

GlennB · 02-08-2010, 12:07 PM

Here you go:

According to AT&T, the ringing signal is an 88v 20Hz A.C. signal superimposed on 48v nominal D.C. supervisory voltage. However, the actual ringing signal used can and does vary greatly from one location to another.

I too have been hit by it in a damp basement, it's a nice little stinger but nothing like 277V, that one burned a hole in my finger thanks to the guy before me that over tightened his wire nut so that the solid wire just barely poked through the end.