White wire became hot all of the sudden

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  #1  
Old 04-27-13, 09:30 PM
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White wire became hot all of the sudden

hello Folks,
just joined this wonderful forum and desperately need your help to resolve my issue.

i bought a brand new townhouse recently and the master bedroom has two huge walk-in closets/dens, so i turned one into an office. sine it was a closet, it didn't have an outlet, so i cut a whole in the drywall to steal a wire right from the other side of the wall (the bedroom) which had an outlet there.

everything was fine for the past 3 months until today that all of the sudden the power went off in the bedroom only when i turned on my Brother Laser printer in the office. checked the switch box to see if it tripped, but it was fine, except now my white wire became hot all of the sudden. i measure about 100 volts AC on white wire and 120 V AC on hot wire, but cant understand or find the source of any short circuiting that may cause this.

would someone be able to advise what else should i check, please?

thanks a bunch in advance!
 
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Old 04-27-13, 09:42 PM
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checked the switch box to see if it tripped
First terminology. You didn't check a switch you checked a breaker in the breaker box to see if it was tripped. Did you turn the breaker all the way off then back on? Often a tripped breaker doesn't look tripped.

now my white wire became hot all of the sudden. i measure about 100 volts AC on white wire and 120 V AC on hot wire,
You measure voltage by measuring between the black and the white wire of a cable. That doesn't sound like what you did. Did you use a digital multimeter or an analog multimeter? The wires of a cable must be disconnected when you measure, were they. You can also measure hot to ground and neutral to ground. Did you do that also?
 
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Old 04-27-13, 10:35 PM
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Hi Ray,

YEs, I guess it is the breaker, but I am still newbie in terminology as you can see. Basically, it is the large box where you can switch the power on/off to various rooms in the house. It was not tripped for sure, because it was all the way to the ON side and the RED tripped indicator was not displayed. I turned it on/off many times, no change.

I used digital multimeter and measured both against the ground wire. When I measured against each other (hot vs white) voltage is zero! But independently against the ground it is measuring 120 and 100 as I stated earlier.

Just can't figure out how the white (I guess also called neutral) has become hot and the breaker didn't trip.
Frank
 
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Old 04-27-13, 10:56 PM
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A cheap digital multimeter may show an incorrect reading because of high impedance. A cheap analog meter is more accurate because its lower impedance tends to cancel out ghost voltages. The ground to neutral is probably actually close to zero volts.

When I measured against each other (hot vs white) voltage is zero
Then the line is dead. The fact you have 120 volts hot to ground indicates an open neutral. You need to check all your connections and move any connections inserted into the holes in the back of the receptacle (back stabs) to the screws. Back stabs are a common point of failure because only a light spring makes contact and it can eventually loosen. The problem may be at the last working receptacle or the first non working receptacle.

Have you read: http://www.doityourself.com/forum/el...ther-info.html
 
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Old 04-28-13, 07:40 AM
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A laser printer can place a large load on the circuit. Any marginal connection will fail over time and can open. Look for a loose connection as scripted in Rays post above.
 
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Old 04-28-13, 07:57 AM
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When I measured against each other (hot vs white) voltage is zero! But independently against the ground it is measuring 120 and 100 as I stated earlier.
Those are the important clues. The 100 volts you get on the white wire is power from the same circuit that is feeding through other loads on the circuit after the open neutral. The open neutral could be at a receptacle or switch box, or it could even be in a junction box or even in the main panel.
 
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Old 04-28-13, 07:19 PM
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I spent couple hours today to go through the last two outlets and now I am convinced, as all of you have suggested, that somewhere the neutral wire has gone loose. The voltage I am reading from neutral, I realized is a simple physics: am image current (or image voltage if I may) that is generated on the "floating" neutral wire which drags along the hot wire, but not due to short circuiting of hot and neutral wires as I earlier thought.

My concern is: since this is a new home and if one printer can cause such floating, should I be concerned in the long term? I sure am going to contact the builder tomorrow.

THanks again!
frank
 
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Old 04-28-13, 09:57 PM
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I sure am going to contact the builder tomorrow.
Are you sure you want to do that after you modified the circuit? Are all of the connections correct for both the receptacle you added and the receptacle where you tapped into the existing circuit?
 
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Old 04-29-13, 05:55 AM
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A poor connection installed when the house was built could be upstream of the new work. The load of the printer could have caused it to fail.
 
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Old 04-29-13, 03:09 PM
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called the electrician today. hopefully this will get fixed soon, otherwise I am afreaid my two year old will pull the extension cord plug hanging in the hallway.
Thanks all for the clues!
 
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