Wiring question

Yes, it is necessarily dangerous. We're discussing specifically pulling a neutral from *another circuit*. The current in the neutral will be whatever currrent is drawn by the load operating on the *other* circuit, not the current in the X10 device.

Reply to
Doug Miller
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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.

Reply to
Doug Miller

That switch itself is in fact a load. A very small one, but it's still a load. If it did not pass current on the neutral, then it would not need the neutral. Could it deliver a serious shock as is? I would agree that it would not, provided everything else is wired correctly, meaning there is no disconnected neutral on the other circuit, etc. But it could cause future problems where someone later comes along and sees that neutral, assumes it is on the same ciruit as the hot and decides they want to use it for something else, like adding more outlets, causing an overload. That is the serious risk you run when you decide to ignore a code rule that is universally followed by almost everyone.

Reply to
trader4

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....

Reply to
Andy

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

Reply to
Andy

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.

Reply to
trader4

Andy comments: Exactly. Now that Ivan has seen the problem from several angles, l think he can make an informed decision about what he wants to do...

Still, I HEARTILY reccommend him putting the X10 module in the fixture where it is used, rather than the wall switch..... if he has room... All the other arguments should be considered, but the convenience of a low current #14 white wire for one simple circuit may be the overriding factor......I am sure that a future electrician will see immediately that a non-standard method has been used and will re-think his options...

Andy in Eureka, Texas

PS Ivan, maybe you can do a search for a battery operated control module.... one that can replace the wall switch but has a couple of AA cells in it for the controller activation.... I haven't seen one, but I haven't looked, either...

Reply to
Andy

Would a multi wire branch circuit meet code and be safe?

Reply to
Dean Hoffman

ts remotely. =A0This would obviate my walking across the room in the dark t= o get to the light switch.

location. =A0Several of my switches have only a hot leg coming into the bo= x with no neutral. =A0X10 docs. recommend simply running a neutral wire int= o the box. =A0

ches are on the exterior walls. =A0These locations are inaccessible from th= e attic since this is where the roof meets the ceiling ergo providing mere = inches of crawl space. =A0It would be much easier to run the neutral wire f= rom below (I have a generous 42" high crawl space). =A0

an I simply come from any circuit (even a separate new circuit) and run a w= hite neutral wire to each switch box? =A0Does it have to be from the same p= hase? =A0X10 docs. do mention that if not from the same phase, then the pha= ses can be joined at the box.

There not talking about the current, if any, from the X10 device. They are talking about the current from other loads on the circuit that the neutral is bootlegged from. If, in replacing the X10 device at some future point in time, the splice in the neutral of the circuit from which the bootlegged neutral was taken were opened the load side of that splice will go high to one hundred twenty volts.

I had such an incident with a bootlegged neutral serving a lighting fixture. I opened the switch to the light and installed a lock out device on it. I checked for other hot circuits in the box with a voltage proximity detector and got no voltage indication. I opened the splice to the neutral, using best practice non contact technique, and got a spark when I actually broke the neutral continuity. So I checked again with the proximity detector and got a voltage indication. I pulled out my Wiggy and got one hundred plus volts to ground. I applied a tracer transmitter between the two disconnected neutrals and it came on and produced a signal. When I opened the fuse it led me to the voltage and the signal went away. I then reapplied the power by closing the fuse and traced the neutral to discover were it actually came from. I was able to rework the circuits arrangement to clear the inter-circuit connection but, had I not used best practice technique, I might have received a fatal shock.

-- Tom Horne

Reply to
Tom Horne

Yes, as long as it is installed in compliance with the Code -- specifically, in reference to the OP's question, with all conductors being in the same cable. A DP breaker will also be required.

Reply to
Doug Miller

It's not up to Ivan to decide what's safe or unsafe. What makes you think Ivan has the technial expertise to even understand the issues involved? The NEC serves the purpose of deciding what is safe and what you claim is OK is a clear violation of NEC. Do you disagree with that?

A future electrician? Is Ivan an electrician? No, yet he's doing the wiring. A future Ivan comes along and expands the circuit using that neutral for other outlets. Or maybe Ivan himself because either he doesn't understand the real issues or 5 years from now he forgets. Or Ivan goes to put in a GFCI on that other circuit and can't figure out why it constantly trips.

Convenience is never an excuse for violating the NEC.

Maybe you should look at the NEC first.

Reply to
trader4

Yes, I know that. You don't seem to understand the concept of parallel circuits. If your body is grounded, and also in contact with the neutral conductor, there are two parallel paths to ground: one through the neutral conductor, and one through your body.

Most of the current will flow through the copper conductors. But it takes only a few tens of milliamps to interfere with heart rhythms.

In the sense that you're equally able to get a shock from each, I'd agree.

An EE that doesn't understand parallel circuits? Yeah, riiiiight.

Reply to
Doug Miller

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.

Reply to
Doug Miller

Along those lines, concerning practical wiring, the whole thing is rather funny, don't you think? We have Andy desperately trying to give Ivan an excuse to go tap in to another neutral. But for what useful purpose? You and I know that in almost all cases, if you can go find another neutral, you can find the hot that goes with it. Last time I checked, Romex comes with two conductors, so what is achieved by running only the neutral back, instead of both the hot and neutral and moving the light entirely to the other circuit? Doing the latter makes it code compliant, standard practice and is no more work.

Maybe Andy the EE can answer that for us.

Reply to
trader4

Well, it would be, if it weren't for the potential hazards.

Don't hold your breath...

Reply to
Doug Miller

But there will be no voltage difference between neutral and ground - so the neutral is still SAFE. ALL neutrals are the same potential = zero volts to ground - unless the neutral is "lifted".

If you shut off the circuit the X10 is used on, the "other circuit" neutral is still zero volts. So it is not an issue.

If you shut off the "other circuit" to work on IT, the neutral from the x10 is not carrying any load - so although a sensitive voltmeter MAY show a voltage, there will not be enough current to shock you. It MAY give you a barely perceptible tingle. and then only, as I said before, if the neutral is "lifted" - ie - the wire from the x10 is separated from the circuit neutral, the circuit neutral is opened somewhere between that connection and the neutral buss (ground) or the neutral is disconnected from the buss.

So the chances that it would EVER be dangerous are extremely remote. It is, however, still against code.

The reason it is against code is because, having the "off circuit" neutral in the box with the live line, someone down the road COULD connect a load to that neutral. As soon as a load is connected to that neutral ALL of the situations everyone is worried about BECOME possibilities. The neutral just for the X10 device is NOT, in itself, a safety issue.

Again - I would NOT recommend it. It IS contrary to code (so you could say it is illegal) - but it is not, necessarily, dangerous.

Reply to
clare

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.

Reply to
clare

If, as I suspect, the switching mechanism in the X10 is a voltage controlled switch (think FET or MOSFET device) there is NO current flow to the neutral.

Howver, you HAVE identified the danger - the POSSIBLE FUTURE danger which makes it illegal and unadviseable to use the "split neutral" configuration. The FACT that the orphan neutral is in the box makes it POSSIBLE for some future person (or even the OP, in the future) to use that neutral to complete the circuit for a REAL load, such as an aditional outlet or lamp. Since it is APPARENTLY possible to bring a neutral up from below, the much better way to approach this is to bring a FRESH CIRCUIT up from below to power this.

Reply to
clare

In an ideal world, perhaps. In the real world, where houses are not wired with superconducting cable, copper wire has a very low but definitely non-zero resistance. And splices in copper wire have a very low but definitely non-zero resistance. And the potential difference between the electrical system grounding electrode and the water pipe, for example, that you're touching is not necessarily zero.

NO IT'S NOT. The neutral carries current.

That doesn't matter. If your body is also at ground potential, and you contact the neutral, your body forms a parallel path for that current to return to ground.

Granted, most of that current will be in the neutral conductor, and not in your body -- but it doesn't take very much to kill you. Why do you suppose the trip threshold on a GFCI is only 20mA?

Wrong again. If there is a load on the other circuit, there is current flowing in the neutral wire. If you touch it while you are grounded, you have formed a parallel path to ground for some of that current to return through your body.

Worse, if you *open* a splice in that neutral, not knowing that it's carrying current from some other circuit, you may have formed a parallel path to ground for *all* of that current to return through your body.

Nobody ever claimed that the tiny current drawn by the X10 device constituted a hazard of any sort.

Right. It's against Code because ... wait for it ... it's DANGEROUS.

And that "someone down the road" could be as simple as someone turning on an appliance in the kitchen while Ivan is installing his X10 gizmos. I would not enjoy being part of the return path for the current drawn by a toaster or microwave oven. YMMV.

Which is exactly what I've been saying all long -- that if there is a load on the other circuit, the current in the neutral is a potential hazard. Thank you for [finally] acknowledging that.

Yes, it is. I hope that you don't ever learn the hard way that you're mistaken.

Reply to
Doug Miller

1ma is the threshold of sensory perception - less than 1ma the average person can NOT detect. 5ma can be considered to be "dangerous" 20-30ma is a strong enough shock that you "can't let go" and at anywhere between 100 and 300ma the heart is affected and death is likely. 6 amps will stop the heart - after which normal rythm can be returned (defibrilator) That is current THROUGH THE BODY. If ALL of that current flows through the HEART MUSCLE, several milliamps CAN be fatal.
Reply to
clare

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