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Wire still hot after breaker turned off

housenut1's picture

The 15A breaker was turned off and I proceeded to tap into the box for an additional light.  It was still hot.  I turned it on and off again and one time it was off and another time the tester's light dimmed slowly to off.  Could it be a bad breaker or possibly a loose connection on this breaker at the panel causing this?  


   

(post #80009, reply #31 of 57)

well to begin with , you are sharing a neutral that you thought was dead with another circuit that is not !
if you want to get a real good jolt, simply keep screwing around with the neutrals in your house.

a common practice is to use ONE neutral with TWO hots, it's cheap and it works and it can cause all sorts of damage to appliances and people when someone like yourself thinks everything is hunky dory because you shut off ONE circuit breaker..

in fact, electricians can get the #### knocked out of them when they are working on commercial lighting that has three hots and one neutral. where the voltage is usually 277

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., wer ist jetzt der Idiot ?
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(post #80009, reply #32 of 57)

you accidently opened a neutral that is shared with another live circuit.


Naw, same circuit.  He said that he had the light swich turned off, not the entire circuit.


But your answer is of course still correct.......he interrupted the neutral to something that was drawing power.


Ed

(post #80009, reply #33 of 57)

yep, bad news either way

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., wer ist jetzt der Idiot ?

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(post #80009, reply #38 of 57)

being a hall light. Is it a 3-way circuit (one switch at each end of the hallway). These can behave strangely.

TFB (Bill)

TFB (Bill)

(post #80009, reply #47 of 57)

Thanks for the advice on testing for a bad breaker.

(post #80009, reply #34 of 57)

Every time I skim down over the list of thread titles, I stumble over this one.

It says wiRe ! Not wiFe...

;o)

A little unexpected act of kindness, goes a long way.


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It's a small world. Until you have to walk home...

(post #80009, reply #35 of 57)

Careful skimming and scrolling, I see ya can get ammonia from painting in cold weather..

Spheramid Enterprises Architectural Woodworks


"If you want something you've never had, do something you've never done"

www.richmondrenovationsandrestoration.com  

(post #80009, reply #36 of 57)

There's a place in Hollywood right now for writing like that. Carpe Diem.

(post #80009, reply #37 of 57)

and I've been staying out of the shower cause I don't want to get scolded by Mom. That is my antiscold shower formula

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #80009, reply #41 of 57)

Yeah, I keep seeing the rude guy on Harley thread.  Ever notice how much rude and nude resemble each other.  I get a very ugly mental picture when I see that thread name.

(post #80009, reply #42 of 57)

Dangit, now I have to remember where I put the brain brillo pads.

A small, unexpected act of kindness, goes a long way.


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It's a small world. Until you have to walk home...

(post #80009, reply #43 of 57)

Some things even brillo can't clean.

(post #80009, reply #44 of 57)

Obviously the neutral was hot because it wasn't vented ;o)


Jeff

(post #80009, reply #45 of 57)

Are you sure she was a nuetral ?

Did you check to make sure the insulation matched at both poles ?

A small, unexpected act of kindness, goes a long way.


.

It's a small world. Until you have to walk home...

(post #80009, reply #39 of 57)

http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Fluke-volt-affects.htm&ID=292


If your view never changes you're following the wrong leader


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #80009, reply #40 of 57)

back feed..

 


Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming


WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!

"Some days it's just not worth chewing through the restraints"

(post #80009, reply #46 of 57)

Thanks for the tip.

(post #80009, reply #48 of 57)

There is a possible reason other than a faulty CB.  This is a really technical answer, but here goes:  The service to most houses is 120/240V; there are two 120V phases which have a common reference point, the neutral (white) which is tied to the grounding system and the ground wires (green) at the service entrance panel.  The voltage difference between the two phases is 240V, usually used for A/C and electric stoves.  The reason for this voltage, rather than both of the phases being the same and the difference being zero, is that the the alternating voltages on the phases are 180 degrees out of phase - when one is positve the other is negative and the +120 and -120 add up to 240.  This means that if you put exactly the same load on each phase, the net current on the neutral is zero.


Electricians sometimes make use of this fact by running a single neutral wire along with two hot ones of different phases.  To comply with the NEC, the circuit breakers on these lines have to have a common-trip mechanism, which is usually incorporated into a two-pole CB.  But people wiring houses don't always do the correct thing, and may either use separate CB's or use a mechanical clip or pin on adjacent breaker handles which can fall off. 


If one phase of a two-hot-wire, common-neutral circuit is open and the other is energized, the neutral current can flow back through loads connected to the open phase and energize the supposedly disconnected line.  If there is no load connected on the active line, then there will be no voltage on the open one.  So if the acative line has a switched load, like a refrigerator or furnace, the voltage on the "open" line can fluctuate off and on.  And, grounding the "open" line will not trip the CB, because there is a normal load on the line and doing so will not create a short circuit.


So, always check the voltage before working on wiring; something I have been forcefully reminded of when I occasionally forget.  And if you think the above is confusing, you should see what three-phase systems are like!


11/27 - I need to make a couple of corrections to this; I was rushing to finish it last night and didn't check the NEC nor make myself a drawing:


1. As BillHartmann pointed out, the NEC allows separate CB's on multiwire branch circuits.  But, ever since I got bitten by one, I've thought they should not allow that, and that idea is what has stuck.


2. I left out an important step in the above scenario.  Assuming that you have a multiwire circuit with two hot wires of different phases and a shared neutral, everything will be okay as long as there is a solid connection for the neutral for all loads.  The worst that will happen is that the disconnected phase will see the line-loss voltage on the neutral - a couple of volts at most.  The problem comes when the neutral is disconnected.  If there are a number of receptacles and/or devices on each phase, one phase is turned off, and the neutral is opened somewhere along the line, the neutral downstream of the open will go to 120V; and if there are loads on the disconnected phase (such as a light with the switch on or a plug-in power supply), the hot side of this will also go to 120V.


The way this can most easily happen is when replacing a receptacle.  The most common method for wiring them is to connect a pair of supply wires to the receptacle and then run another pair of wires to the next one.  Removing a receptacle in the middle of the "daisy chain" opens both the neutral and the hot to the following receptacles.  If the power is from a multiwire circuit, the above situation can then occur.  To make things worse, checking the wires with a tester or voltmeter won't tell you what is going on, since the voltage won't appear until the neutral line is opened.  An what actually happens depends on what is connected to each phase at the time and in what order the wires are disconnected.


The preferred method for connecting receptacles (and required in some jurisdictions) is to tie each set of wires in the J-box together with a pig-tail using a wire nut, and then connect the pig-tails to the receptacle.  That way the circuit is not interrupted when the receptacle is removed. 


 


 


 


Edited 11/27/2007 12:30 pm ET by brod

(post #80009, reply #49 of 57)

"Electricians sometimes make use of this fact by running a single neutral wire along with two hot ones of different phases. To comply with the NEC, the circuit breakers on these lines have to have a common-trip mechanism, which is usually incorporated into a two-pole CB."

That is not correct.

240.20
(B) Circuit Breaker as Overcurrent Device Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.20(B)(1), (B)(2), and (B)(3).

(1) Multiwire Branch Circuit Except where limited by 210.4(B), individual single-pole circuit breakers, with or without identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.

210.4 Multiwire Branch Circuits
(A) General Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard or similar distribution equipment.

(B) Devices or Equipment Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates.

(C) Line-to-Neutral Loads Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.

Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

"If one phase of a two-hot-wire, common-neutral circuit is open and the other is energized, the neutral current can flow back through loads connected to the open phase and energize the supposedly disconnected line."

In a case like that the on way that there would be voltage on the "open" leg would be if there is a 240 active load between the 2 legs. And there would not be current flowing unless there was also an active 120 load on the bad leg as the same time as there is an active 240 load.

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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #80009, reply #50 of 57)

That's interesting, well researched and not at all helpful.


Always test before handling, no matter how sure you are about a circuit.


Never assume code was followed. A cheap tester is $10. Be safe.

(post #80009, reply #51 of 57)

Brod:


Thanks for the thoughtful insight and education.  I will keep the information in a special file for future refrence.  As a remodeling wannabe there was one point I did right and that was the correct wiring of the receptacles as you stated.


Sincerely,


Housenut1

(post #80009, reply #53 of 57)

Was once trying to figure out some illigically run wiring, and kept reading around 50 volts at very low amperage (not really enough to bite) with even the main switched off.  My first thought was of perhaps a computer UPS, but no.  Disconnected the main and still got the reading!  Pulled the meter and still got the reading!!!  House was built about 70 feet from large overhead high-tension towers.  I couldn't get anyone to verify the possibility that what I was reading was radiation, but never found any other source.


}}}}

(post #80009, reply #54 of 57)

That is called phantom voltage.

It is casued by capacitive couple between other "circuits".

Very commonly seen in a house when using a digitial voltmeter.

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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #80009, reply #55 of 57)

Ted:


Thanks for the story.


Housenut1

(post #80009, reply #56 of 57)

One part of my lumber yard is right under some hi-voltage lines. If you stand in your truck with a flourescent bulb in your hand, the thing will light up. That would make me nervous working under those!


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #80009, reply #57 of 57)

Was once trying to figure out some illigically run wiring, and kept reading around 50 volts at very low amperage (not really enough to bite) with even the main switched off.  ...House was built about 70 feet from large overhead high-tension towers.  I couldn't get anyone to verify the possibility that what I was reading was radiation, but never found any other source.


The voltage is induced in your house wiring through coupling of the magnetic fields produced by the high tension wires.  It's called "inductive coupling".


If you wiki "phantom voltage" there is a more detailed explanation.

(post #80009, reply #52 of 57)

"The preferred method for connecting receptacles (and required in some jurisdictions) is to tie each set of wires in the J-box together with a pig-tail using a wire nut, and then connect the pig-tails to the receptacle. That way the circuit is not interrupted when the receptacle is removed. "

FWIW the NEC specifically calls that out for multwire circuit.

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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe