The Real Tom wrote:

On 13 Mar 2005 14:02:55 -0500, wrote:


m Ransley wrote:


I think 30v is more than induced curent...

It's voltage, not current, and easy to see on an open circuit next to a
powered conductor... 120 V across 10 pF/foot over 100', ie 1000 pF, ie
1/(2Pi60C) = 2.6 meg in series with a 10 meg meter would make it show 95 V.

You seem very determined to show your ignorance :-)

Nick



Redo your problem Nick, your problem solving for was for a single
conductor, and measuring voltage end to end.

Not the way I read it Tom. The voltage measured end to end on that
isolated conductor would be zero.

I believe he was describing a single isolated conductor running near one
with an ac voltage on it. The 95 V he mentioned would be measured
relative to the other side of the ac source swinging that powered
conductor (Which would of course be "neutral" and/or "ground" in a
home.) That voltage would be the same anywhere along its length.

He really should have described the most likely case; that the isolated
conductor in a home wiring system would be a black wire in a length of
Romex and the white wire and ground leads in that Romex would be
connected to the other side of the ac source (ground). So, there would
be a fair amount of capacitance between the isolated conductor and the
two grounded ones in the Romex, probably more than the amount per foot
he estimated for a "nearby" powered conductor. That would create a
capacitive voltage divider, so the voltage measured on the isolated
conductor couldn't possibly reach the 95 V level he mentioned.


Not for two(or more)
conductors running side by side, and measuring voltage at one end.
The voltage induced in one conductor, would be exacly the same as the
induced in the others, therefe for no potential would exist between
the conductors(as in OP's story) where the voltage should be sensed,
between the conductors and an immediate grounding source(not the ECG,
since that is one of the parallel conductors).

I'll give you an A for effort, Faraday would be proud. :-P

BTW, the NEC covers taking steps to minimize induced voltages and
inductive heating, even for common fokes, it gives enough information
about how running conductors close together will reduce/elminate it.

Twisting the conductors really helps with the inductive heating stuff.

Just that I see often that digital meters show voltage, on dead legs,
and I've chatted with others about how to ensure you have no juice
left. One smart chap said, cind the ECG and Neutral are bonded, why
not bond the ungrounded(hot) conductors, we cam up with an idea that
you can bond all three with a shorted out three prong plug. Now
voltage should be ZERO, but we figured come time to close the breaker,
we would forget it in place, and melt it.

later,

tom


Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"