Wiring question

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Want to install several X10 relay switches in the house to turn on lights remotely. This would obviate my walking across the room in the dark to get to the light switch.
Problem: The X10 switch/relay requires full power at the wall switch location. Several of my switches have only a hot leg coming into the box with no neutral. X10 docs. recommend simply running a neutral wire into the box. Question: Most of my wiring is within the attic and some of the switches are on the exterior walls. These locations are inaccessible from the attic since this is where the roof meets the ceiling ergo providing mere inches of crawl space. It would be much easier to run the neutral wire from below (I have a generous 42" high crawl space). Question: Does this neutral have to come from the same circuit? Can I simply come from any circuit (even a separate new circuit) and run a white neutral wire to each switch box? Does it have to be from the same phase? X10 docs. do mention that if not from the same phase, then the phases can be joined at the box.
All comments, advice and suggestions appreciated.
Ivan Vegvary
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Andy comments: The neutral (white) wire is not phase sensitive, so it can come from anywhere. However, it will NOT meet code, if that is a concern...
Have you considered the idea of using a table lamp and an X10 module at the wall plug ?
I really sympathize with your plight of trying to add wiring in an exterior wall.... I hope some genius on this newsgroup will post a response showing a simple way to do it, but it is beyond me....
Andy in Eureka, Texas , PE
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They make a motion sensor wall switch that works off only the hot leg in the switchbox. You can try that as an alternative.
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On Fri, 16 Sep 2011 03:27:01 -0700 (PDT), Mikepier

This is my vote.
A warning though, once you start putting in motion switches, you will want them everywhere. I started in the kitchen to keep the girls from using the fridge as a night light (low intensity lighting on a M/D) Then came the bathrooms with the toe kick lights and it continued into the hall. Now when you walk around at light, the lights follow you and you are never looking for a light switch in the dark. These are all low level lighting. Most of it is rope light concealed in cornices, toe kicks etc.
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On 9/16/2011 6:01 AM, Andy wrote:

It's not just a question of whether it meets Code or not. This is also a safety issue. What you propose is dangerous:
The neutral conductor carries the same current as the hot conductor. When two circuits are cross-connected to use the same neutral, the current in the neutral is the *sum* of the currents in the two hot legs. A current of 15 amps in each of two hot legs will result in a 30A current in the neutral. This risks a fire.
Also, someone working on one circuit and not knowing that the neutral carries current from a different circuit could receive a fatal shock from that neutral -- how would he know to shut down both circuits?
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wrote:

Andy comments: I am confused as to how you think someone could receive a shock from the "neutral" wire... It is normally not disconnected in any configuration --- only the black (red) hot lead.... All neutrals are connected together, without interruption or disconnects, in the panel... Except for current carrying capability, they are the same wire....
In Ivan's use, the additional current, if any, carried by the neutral is very very very low --- certainly less than an ampere, and would not screw up anything.... He just wants to put in a simple relay module....
Other than that, you are correct, and it's only necessary to let Ivan know of the risk... Personally, rather than rip out a wall to rewire an outlet, I'd probably do it...
Mikepier's idea of a motion sensor that works on just the hot line sounds good to me, too...
However, if there is room in the fixture for the light (or whatever) I'd just put the module in there, since black/white/copper will be present anyway....
Andy in Eureka, Texas P.E.
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On 9/16/2011 6:43 PM, Andy wrote:

Because it carries current. The same current that's in the hot.

It doesn't really matter whether it's disconnected or not. It's carrying current.
Consider two simple circuits, A and B, each supplying no loads other than a single 100W light bulb, each of which is turned on -- but, unbeknowst to you, their neutrals are cross-connected. Well and good. Now suppose you need to replace the fixture on circuit A. Knowing that it's on circuit A, you shut off that breaker, and disconnect the hot lead to the fixture. Now when you go to disconnect the neutral lead, you get a shock, because -- and I think this is the point you are missing -- electricity doesn't "follow the path of least resistance" as many people believe, it follows *all possible paths*, including the one that you've just made with your body by touching that energized lead.
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Huh?
The reason you don't use the "wrong" neutral is just the subtle effect of poor cancellation of the magnetic field generated by current carrying conductors. If the conductor and it's neutral are close to each other their magnetic fields cancel.
The main time neutrals can produce a dangerous situation is when, somehow, they get dis-connected from the power source (either at the service/breaker panel or in an intermediate junction box.) Any kind of a load will make a white wire (your neutral, HOT, HOT, HOT!
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No. As has been explained to you there are two very real problems with using the neutral from another circuit and why it's a serious code violation.
1 - As Doug explained above, when doing a repair, you shut off the breaker to circuit A. If that neutral on that circuit belongs only to it, then you can't get a shock. If on the other hand the neutral is actually connected to circuit B which is still energized and has an active load, then current is flowing in that neutral. Exactly what your chances of getting shocked are will vary depending on how it's wired.
Worst case, consider that the neutral arrives in the wall box you happen to be working on. It comes from the other energized circuit's load, into a wirenut that is pigtailed to the switch. Also connected to the wirenut is the neutral wire going back to the panel. You take off the wire nut. Now you have 120V on the neutral coming from the other circuit in your hand. If you happen to be grounded, you complete the circuit.
Best case is you just tap off another neutral and the neutral just ends where you're using it. Even then as Doug pointed out, current divides depending on resistance. Grab that wire while you're grounded to something and some current will flow through you as you are now an alternate path back to the panel.
2 - Conductors are sized for the circuit they are serving and for the corresponding breaker. By sharing a neutral, you could put not only the current from circuit A through it, but also the current from circuit B, exceeding the safe current for that conductor by 2X or even more.

Which would include the poor guy who turns off breaker A then disconnects the neutral, not knowing that the neutral is actually connected to circuit B.
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On 9/16/2011 11:02 PM, John Gilmer wrote:

I know that. But that's completely unrelated to the shock danger.
You *can* get shocked by the neutral.

Even if the neutral is not disconnected, if you make, with your body, a parallel conductive path from the neutral to ground, *most* of the current in that neutral will indeed return to ground through the neutral conductor -- but *some* of it will return through your body, as well.
Electricity follows *all possible paths*. Don't use your body as one of them.

And that makes your body the *only* path for the current to flow through. Your mistake is in thinking that this is the only dangerous condition. It's not.
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On Sat, 17 Sep 2011 09:30:34 -0400, Doug Miller

IF the neutral connection is "adequate" - less than 1/2 ohm, let's just say for arguement's sake, and your body resistance is lower than normal (let's just pick 500 ohms out of thin air) and the load current is 15 amps (anything more would trip the supply side breaker) what current would flow through your body???? The voltage drop across the .5 ohm ground connection would be 7.5 (15 ampsX.5 ohms)volts. The current through your 500 ohm body would be less than 15 ma.
A .5 ohm ground connection would show up as an obvious problem with a 7.5 volt drop and 112 watts of heat dissipation at the ground connection. A much more common (or let's say POSSIBLE situation is a .05 ohm ground connection - with a 0.75 volt drop, dissipating 11 watts of heat at the bad connection (still very noticeable as a bad connection) where the current flow through a 500 ohm body resistance would be less than 1.5 ma.
Now substitute a much more realistic body resistance (with wet skin) of 10,000 ohms and you can see how rediculous your arguement is. 7.5 volts across a 10,000 ohm resistance is 0.75 ma of current.
Go to a DRY SKIN situation, with body resistance of 450,000 - 495,000 ohms, and you see where we are headed??????? We are aproching 1.5 e-5 amps. that's something like 0.0015ma if my exponential math is correct. And that is with the VERY BAD 0.5 ohm ground.

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On 9/17/2011 8:10 PM, snipped-for-privacy@snyder.on.ca wrote:

Certainly not a realistic situation. 14AWG copper has a resistance of approximately 3 milliohms per foot, so your hypothetical 50 milliohm resistance represents just seventeen feet of 14AWG copper. I submit that most points in most residential circuits are a *lot* farther than 17 feet from the panel.

Do you have references for any of these numbers, or did you just make them all up like the 500 ohms you "picked out of thin air" a couple paragraphs back?
The resistance figures given here http://en.wikipedia.org/wiki/Electric_shock#Body_resistance are FAR lower than yours. I think I can be pardoned for believing documented numbers from NIOSH and the IEC just a bit more than I believe your numbers "picked out of thin air".

It's not.
It also assumes your resistance figures are correct -- which I very, very much doubt.
Do your calculations again, with realistic resistance figures this time (both for the human body, and for the neutral wire), and see where it leads you.

500 milliohms is the resistance of approximately 170 feet of 14AWG copper; there is at least one 15A circuit in my house where the last outlet is very nearly that far from the panel. What makes you think that indicates a "VERY BAD" ground?
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On Sat, 17 Sep 2011 21:31:38 -0400, Doug Miller

32 feet of 14 ga copper has 82.8 milli-ohms of resistance. At 15 amps, that is a total voltage drop of 1.23 volts at 15 amps. That is OVER AND ABOVE the resistance of the "connection" I was refering to.
So lets say the wire is 32 feet long - from the point where you are working on the circuit - and we have my theoretical .05 ohm connection resistance for a 2 volt drop. That's a 30 watt total dissipation. and a current flow through the 500 ohm body of less than 4 milliamps.

My 500 ohms "picked out of thin air"s actually pretty darn close, according to my sources noted below.

I had gotten the same numbers from several sites that I looked at - which appear, according to your Wikipedia reference to be out by a factor of 10 but I don't take Wiki information as gospel. My primary source was www.ohmcheck.com/human-electrical_resistance.htm Also look at http://www.allaboutcircuits.com/vol_1/chpt_3/4.html Also, http://www.tlc-direct.co.uk/Book/3.4.2.htm uses 500 ohms resistance as "worst case" resistance.
Page 220 of http://www.angelfire.com/mech/electrical_accidents/files/electricalshockstandards.pdf indicates 500-1000 ohms as the minimum resistance of the body EXCLUDING SKIN RESISTANCE. The resistance of "intact dry skin" according to the same sourse is "quite high". These resistances are between any two limbs. Resistance across the chest - say laying on the ground with a defective tool on a bare sweaty chest could be as low as 100 ohms.
Another reliable source, in my eyes, is http://www.hubbellpowersystems.com/literature/encyclopedia-grounding/pdfs/07-0801-02.pdf which indicates 2330 ohms hand to hand and 1130 hand to foot according to measurements done by Charles Dalziel in the 1940s and 50s.

Regardless, we are talking running that circuit at FULL LOAD - so even with YOUR numbers, it is far from "dangerous"
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On Sep 17, 11:30 pm, snipped-for-privacy@snyder.on.ca wrote:

Andy comments:
CL, I am reminded of a quotation from Mark Twain :
"Never try to teach a pig to sing....... It wastes your time, and annoys the pig "
---- Mark Twain
I'm sure that both of us have better things to do .......
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On 9/18/2011 9:56 AM, Andy wrote:

That's pretty much the same conclusion I'd reached in regard to attempting to explain the concept of parallel circuits to you.
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On Sat, 17 Sep 2011 21:31:38 -0400, Doug Miller

32 feet of 14 ga copper has 82.8 milli-ohms of resistance. At 15 amps, that is a total voltage drop of 1.23 volts at 15 amps. That is OVER AND ABOVE the resistance of the "connection" I was refering to.
So lets say the wire is 32 feet long - from the point where you are working on the circuit - and we have my theoretical .05 ohm connection resistance for a 2 volt drop. That's a 30 watt total dissipation. and a current flow through the 500 ohm body of less than 4 milliamps.

My 500 ohms "picked out of thin air"s actually pretty darn close, according to my sources noted below.

I had gotten the same numbers from several sites that I looked at - which appear, according to your Wikipedia reference to be out by a factor of 10 but I don't take Wiki information as gospel. My primary source was www.ohmcheck.com/human-electrical_resistance.htm Also look at http://www.allaboutcircuits.com/vol_1/chpt_3/4.html Also, http://www.tlc-direct.co.uk/Book/3.4.2.htm uses 500 ohms resistance as "worst case" resistance.
Page 220 of http://www.angelfire.com/mech/electrical_accidents/files/electricalshockstandards.pdf indicates 500-1000 ohms as the minimum resistance of the body EXCLUDING SKIN RESISTANCE. The resistance of "intact dry skin" according to the same sourse is "quite high". These resistances are between any two limbs. Resistance across the chest - say laying on the ground with a defective tool on a bare sweaty chest could be as low as 100 ohms.
Another reliable source, in my eyes, is http://www.hubbellpowersystems.com/literature/encyclopedia-grounding/pdfs/07-0801-02.pdf which indicates 2330 ohms hand to hand and 1130 hand to foot according to measurements done by Charles Dalziel in the 1940s and 50s.

Regardless, we are talking running that circuit at FULL LOAD - so even with YOUR numbers, it is far from "dangerous"
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Andy writes: Absolutely correct, and this "dangerous situation" is not part of Ivan's problem.....Although I would suggest that he, like EVERYONE, should check his panel every couple of years to make sure all the little white wires are screwed in securely to the neutral bar ...... ..... and also the little bare copper wires... just for safety....
Andy in Eureka, Texas
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wrote:

Andy comments:
You are incorrect. I suggest you actually try it. Both neutrals are connected together, HARDWIRED, at the sub panel... You are no more likely to get a shock from one as from the other...
But, I'm not here to argue with you... My input is to Ivan... He is smart enough to read all the inputs and decide for himself...
Andy in Eureka, Texas, Licensed Electrical Engineer....
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They are in fact wired together and I see your reasoning. Now consider this. The hardwired together theory works if there is no resistance in the netural wires all the way back to the panel. In the real word there is some resistance in the neutral wire of the second energized circuit along the way. Resistance of the wire, any connection points, eg wire nuts, etc. Now if the second circuit is energized and carrying 15 amps, there will in fact be some small voltage potential there relative to ground. So, it's not the same as the neutral for the disconnected circuit. It's not likely to be enough to shock you, but that is provided EVERYTHING ELSE IS WIRED AND WORKING PROPERLY ON THE OTHER CIRCUIT.
And leaving that neutral there opens up the possibility that someone else will come along someday, see it, and decide to tap on to that circuit for something else, eg new outlets, loads, etc. Now you have a conductor inadequate for the overload protection. It also screws up GFCI protection, whether now or in the future.
I'm surprised that an EE woudl in essence give an OK to what most of us consider a serious code violation.
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On 9/17/2011 9:44 AM, snipped-for-privacy@optonline.net wrote:

It doesn't surprise me at all. Most of the EEs that I've met or talked with don't understand a damn thing about residential electrical wiring.
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