A little electricity 101 if you please

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I'll answer only on the telephone thing. I've forever stripped phone wire with my teeth, BUT, be advised from my understanding, there will be about 90 volts DC if the phone were to ring.
--
Steve Barker


"Eigenvector" <m44 snipped-for-privacy@yahoo.com> wrote in message
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On Sat, 10 Feb 2007 16:45:04 -0600, "Steve Barker"

Put the phone wires in your mouth and you can see when someone's calling :-)
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wrote:

I'll get right on that <GRIN>.
-- Oren
"Well, it doesn't happen all the time, but when it happens, it happens constantly."
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wrote:

I've had such a thing happen (unintentionally) before. There was a problem (since fixed) with the cable here. If you disconnect the cable, you get 30VDC between the shields. This disconnection was at moth level and the loose end hit me (I really don't remember how BOTH ends did at the same time).
--
Mark Lloyd
http://notstupid.laughingsquid.com
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Eigenvector wrote:

Check back, this idiot does NO research as the questions have been asked and answered many times! So don't waste yours.
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If you are standing on a conductive surface such as possibly a damp concrete floor, or if your hand comes into contact with a metal junction box or other grounded surface, you could still get a serious shock. That's one reason electricians favor wooden or fiberglass ladders.

Correct. It's worth noting however that most meters, are sometimes _too_ sensitive and will read "phantom" voltages. A solenoid-type tester or a test light is often easier to use as well as better suited to checking for presence of voltage.

IIRC they can be in the 90 volt range when ringing. I believe the current is limited to a non-fatal value but I can state from personal experience that a telephone wire can give an unpleasant shock.
--
Often wrong, never in doubt.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf.lonestar.org
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(Larry) wrote:

Care to explain how that's going to happen with the breaker off?
--
Regards,
Doug Miller (alphageek at milmac dot com)
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wrote:

Well not answering for him, but I was asking about this in the off-chance that the breaker might not have been off. I was more interested in whether or not a shock is possible when all you're touching is two hot wires - obviously when the breaker's off you shouldn't get shocked (but that's why you measure it with a meter first) at any time. I realize that this is one of those questions where I'm treading on dangerous ground and the responses need to be stated carefully so as not to mislead someone reading it who may not have been following the whole conversation.
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Of course it is. A shock is possible when you're touching *one* hot wire. And it's also possible when touching the *neutral* wire, if the circuit is energized.

Right, and that's also why you test the meter first, by measuring something that's known to be live.

If the right breaker is off, and everything has been wired correctly, you can't get shocked.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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People said: <...snipped...>

<...snipped...>
Actually, I read the OP too quickly and thought that the question was worded as "OR" rather than "AND" OTOH, if I am working on a job where I feel it is necessary to shut off the breaker, I would still use my old Ideal tester before I touched any bare wires. Especially in older houses; just too much is possible.
--
Better to be stuck up in a tree than tied to one.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf.lonestar.org
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If there are two hots, the chances are they're opposite polarity. Otherwise, why would there be two of them?
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On Sun, 11 Feb 2007 13:11:41 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Maybe it's the breaker you THOUGHT was off, or there's another circuit in there and you don't know it.
--
Mark Lloyd
http://notstupid.laughingsquid.com
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Yes, of course -- but the question asked was whether it was possible to get shocked with the breaker turned off. Turning off the *wrong* breaker is not the condition specified in the original question.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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On Mon, 12 Feb 2007 00:28:53 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Of course, anyone can (and does) AT ALL TIMES distinguish between "knowing the breaker is off" and "thinking the breaker is off, but it isn't".
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Hence the large number of responses, mine included, advising the OP to test first anyway. The point remains that it is not possible to get a shock from a circuit that is not energized -- which is what the OP asked about.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Well... Absent broadcast power, big static charges, and huge motors winding downs....
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On Sun, 11 Feb 2007 02:25:05 +0000 (UTC), snipped-for-privacy@sdf.lNoOnSePsAtMar.org (Larry) wrote:

It might be useful if the meter had a button you could press to add a load and see if the voltage changes.

Here, I've measured 50VDC on a phone line with no load. I don't have any current measurements for it, but I do notice the impedance to be high (any load will lower the voltage you see). The ring signal is 75VAC superimposed on the DC so it varies from -25V to 125V. I think the impedance of the ringing signal is much lower, allowing significant current.
--
Mark Lloyd
http://notstupid.laughingsquid.com
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Eigenvector wrote:

Generally true. But you COULD have flipped the wrong breaker (or there's some unknown mis-wiring) AND be, yourself, a path to ground (neutral).

True.
That'll work - unless someone calls at the instant you've got the wires in your mouth. The ring voltage is north of 50 volts.
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wrote:

And don't forget that 50V line voltage is present too. Since that is DC and the ring is AC, the voltage on the line is varying from the difference to the sum of those.
--
Mark Lloyd
http://notstupid.laughingsquid.com
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Phone circuit has approx 50 volts DC idle and approx 80 volts AC ring voltage. will cause curse words to come out of your mouth or worse if you have a bad ticker.
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