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07-15-2013, 05:08 PM   #46
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Quote:
 Originally Posted by Philly Master Dead end to me is a 3 way switch that the 14/3 or 12/3 ends in that switch box with no other wires.....
that also.

 07-15-2013, 06:06 PM #47 Civil Engineer   Join Date: Mar 2009 Location: Boston Posts: 5,639 Rewards Points: 4,858 "Electricity takes the path of least resistance." This is one of the most commonly held, INCORRECT beliefs about current. Any time there is a potential (voltage) difference between two points, there will be current flow between the two points. The amount of current is easily computed, it is I=V/R, where V is the voltage difference, and R is the resistance in ohms. If there are multiple possible paths (a parallel circuit), the amount of current on each path is computed by Ohm's law, based on the fact that in a parallel circuit the voltage drop across any path is identical, only the resistance between different paths is different. So electrical current takes ALL POSSIBLE paths in flowing from A to B, where A and B are at different potentials. If one or more of the possible paths happens to have high resistance, little current flows on that path, but the implication that somehow the current makes a decision about which path has the lowest resistance, and only takes that path, is incorrect. "Volts don't kill you, amps do". This is closer to the truth than the first quote. It is possible to die from as little as 30 milliamps at household voltage levels. There have been numerous studies of electrocution potential, I will not go into the grizzly details here. For a full discussion about this somewhat unpleasant topic, see https://en.wikipedia.org/wiki/Electric_shock. The key thing to understand is that current flow is directly proportional to the potential difference between two points (the voltage drop). By Ohm's law, I=V/R, so the greater the voltage drop, the greater the current. This is why a 240 volt circuit is more dangerous than a 120 volt circuit. Careful reading of the Wikipedia article indicates that approximately 600 volts is the cutoff between current flow over the skin, and dangerous internal heating of the skin causing burns due to subcutaneous current flow. "The purpose of insulation is to prevent fires". This is incorrect. The term "insulator" unfortunately applies both to materials which impede the flow of heat, and which impede the flow of current. For electrical wires, the purpose of the insulator is to confine the flow of current to the wire, by providing an electrically insulating blanket around the wire which eliminates (under normal conditions) any potential for wire to wire faulting. The electrical insulator is not intended to, nor does it, reduce the internal temperature of the copper wire under load. In fact, after a relatively short period of time under load, the temperature of the electrical insulation will rise approximately to the temperature of the wire. Since copper melts well over 1000 degrees C, and most insulators are only rated to at most 95 degrees C, the insulation fails (and often burns) under fault conditions long before the copper melts. If it were not necessary to electrically isolate the wire, electrical insulation would not be used at all, and in fact many utility class conductors are bare aluminum, and rely on air as the insulator between phases on typical three phase lines, and porcelain insulators for support at the poles. For an interesting discussion on insulators, see http://www.wisegeek.com/what-is-an-insulator.htm.
 The Following User Says Thank You to Daniel Holzman For This Useful Post: dgfit (07-15-2013)
07-15-2013, 06:13 PM   #48
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Here is a writeup on elevated neutrals in distribution systems. Unfortunately it is for a 230V system, not 120V. But the principle is the same.
http://electricalnotes.wordpress.com...-distribution/

Quote:
 I thought a floating neutral (as it applies to residential) is when the neutral conductor (which also happens to be the grounded conductor) is lost which would allow the legs to rise above 120
Both legs do not elevate. In the case of load on one leg, you have a voltage drop on the leg as measured to true earth. The neutral rises the same amount to true earth. The opposing leg is still 120V to true earth, but rises by the amount of the neutral voltage.

Quote:
 Are you saying, for example, that if the neutral is lost at the pole then the two legs would not rise above 120 as long as the neutral remains grounded at the service?
No. I was talking about loosing the ground to the center tap, not opening the neutral at or near the transformer.

 The Following User Says Thank You to Oso954 For This Useful Post: dgfit (07-15-2013)

 07-15-2013, 06:18 PM #49 Remodel and New Build GC     Join Date: Sep 2010 Location: Colorado @ 7651' Posts: 5,307 Rewards Points: 3,392 As normal/usual... and expected ....Dan.... excellently explained and clarrified.... Thank Ya I don't seem to have a "thankyou" button on the screen Best __________________ Never stop learning (xcep fer speling en typeing)
 07-15-2013, 07:28 PM #50 Member   Join Date: Jun 2013 Posts: 332 Rewards Points: 282 Thanks for all the info. I will read and digest. Appreciate the dialog.
07-15-2013, 09:40 PM   #51
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Quote:
 Originally Posted by dgfit Thanks for all the info. I will read and digest. Appreciate the dialog.
I agree. It's always interesting to learn.

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