both black and white wires hot

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Old 09-19-08, 08:02 PM
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both black and white wires hot

like the title says both wires (black and white get or turn hot).

when i first test the home run cable ? ,that goes to breaker

box , the black is hot and the neutral not. I have read that in

a two wire 120 volt circuit the white wire is not a neutral , it is

a grounded wire? i use armored cable, black and white wires in

armored cable. i tested the home run cable by touching the

tester to the black and white wire, i get a light. when i touch

from black to the box i get a light. when i touch from white to

the box , nothing which is as it should be? right? i connected

a fan with a light kit to the end of the run , both the fan and

the light are controlled by pull chains. i connected both the

blue and black wires to the black and the white to the white. if

the fan or light is on and i disconnect the white wires at the

home run box , the white wire coming back to the home run

box is 120 volt. i test the white wire coming back to the box

by touching the white to the box , 120 volts. Is this how it

should be? thank you
brian
 
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Old 09-19-08, 09:27 PM
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In 120/240 volt residential wiring the white is neutral, equal potential between both hots, because the winding of the transformer is taped in the center. It is also called the Grounded conductor. ( As opposed to the grounding or equipment grounding conductor which is the green or bare wire)

To answer your question, Yes, that is correct. The reason you are getting 120 volts when the fan/light is on is because the voltage is feeding trough the motor or the light bulb (or both). This is also why you should always be careful when working on neutrals. You can get shocked if you touch the neutral and something grounded when there is a load on it.

BTW - Nice double space!
 
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Old 09-19-08, 09:57 PM
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both wires hot

Thank you very much for your answer.

i am not electrical minded.

i did know i could and did get shocked by a "normal" neutral.

perhaps you are correct.

but any other time i have checked a neutral with a tester

(even though there is "used electricity running through the

wire"), the tester light does not light up.

For the record i am talking about a 120 volt circuit.

i am not going to pick. but...something i read.

between the transformer and the service equipment, the

grounded wire is a neutral wire. there cannot be a neutral in a

2 wire circuit. not my words. thank you, brian
 
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Old 09-20-08, 04:03 AM
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Neutral shocks are actually more dangerous than ground shocks, because they will not cause the breaker to trip. From the breaker's perspective, all you have done is add another fraction of an amp to the load... even though that fraction may be killing you. This is partly why GFCI protection is so useful, it reacts to small amounts of current going someplace it shouldn't be.

The reason you get 120V off that white wire is because you disconnected it. At that point it ceases to be a neutral/grounded wire. What you are measuring is the end of a hot wire that just happens to include your fan fixture as part of its run. The white wire that runs back to the panel, that should have no voltage between itself and ground, because it's still a grounded/neutral wire.

You are misunderstanding what that thing you read means. In order for a wire to be defined as a neutral, it has to originate at the center point of a transformer coil. That means there are two hot points and one neutral... three wires. However, both hots don't have to exist at any location for that neutral wire to remain a neutral. In fact, one hot could not be run at all... but you still have a 3-wire transformer design. Having two wires within a box doesn't change that.

One last note about terminology: Nowadays most any neutral is also a grounded wire. However they are not the same thing... if the wire going from your service disconnect to a ground rod were to corrode or come loose, the neutral would cease to be grounded, and the hot wires could become more than 120 volts to ground. An unsafe condition to be sure. So neutral and grounded wire tend to be interchangeable when discussing properly wired systems. Even though form an engineering standpoint, some grounded wires aren't neutrals, as they don't originate from the center tap of a xfmr.
 
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Old 09-20-08, 08:58 AM
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Originally Posted by mukansamonkey View Post
One last note about terminology: Nowadays most any neutral is also a grounded wire. However they are not the same thing... if the wire going from your service disconnect to a ground rod were to corrode or come loose, the neutral would cease to be grounded, and the hot wires could become more than 120 volts to ground. An unsafe condition to be sure. So neutral and grounded wire tend to be interchangeable when discussing properly wired systems. Even though form an engineering standpoint, some grounded wires aren't neutrals, as they don't originate from the center tap of a xfmr.
All neutrals are the grounded conductor but not all grounded conductors are neutral. Neutral means that it has equal potential (the same voltage) between it and an ungrounded conductor (a hot) Systems that the grounded conductor is also neutral are (but may not be limited to) 120/240 single phase, 120/208Y 3 phase, 277/480Y three phase. System where the grounded conductor is not neutral is (but not limited to) 120/240 delta three phase.

ALL grounded conducters originate in the transformer and have nothing to do with the ground rod. *note I'm talking about the grounded conductor, not the grounding conductor* If you removed your grounding electrode conductor (the wire going from your service to your ground rod) from the ground rod and checked your voltage in the service you will find that nothing has changed. I know this because installing the ground rod is one of the last things we do when changing out a service.

I understand your talking about a two wire circuit but this dose not matter because your service is 3 wire. (2 hots and a neutral) If you take off the black wire on the breaker (with the neutral connected) and with your fan/light on, check voltage between your breaker and the black wire you will also get 120 volts. Why? Because the neutral part of the circuit also goes through the bulbs and motor. Just remember that electricity is not consumed like gas, it is the flow of electrons similar to water, and that flow goes both directions. If you have a complete circuit with a load attached to it, any were you break the circuit and take a reading, you will get 120 volts. (or the applied voltage)
 
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Old 09-20-08, 11:19 AM
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For the record i am talking about a 120 volt circuit.
i am not going to pick. but...something i read.
between the transformer and the service equipment, the
grounded wire is a neutral wire. there cannot be a neutral in a
2 wire circuit. not my words. thank you, brian
Hi Brian

If I may make some clarifications...what you have said above is essentially correct.

A true neutral only serves to carry the unbalanced load (amps) of two or more ungrounded conductors. You cannot have a neutral wire in a two wire modern electrical system. The white wire in, for example, 14/2 armored cable or 14/2 m-b romex is a grounded leg not a neutral because it does not have potential to two or more ungrounded hot wires on different legs and therefore carries all the amps that appears on the single hot wire.
A neutral does not have to originate at a transformer though neutrals will be bonded to the service neutral at the service equipment. For example a range or electrical clothes dryer branch circuit has a neutral wire as the appliances are 120/240
and the white wire carries the unbalanced load created by the 120 volt requirement.

Probably the best example in a homes electrical system is the service neutral coming from the serving transformer. These are generally transformers delivering secondary voltage of 120/240 volts. Each ungrounded conductor of the service entrance serves a bus in your main panel (service equipment). These ungrounded conductors have 120 volts of potential to the service neutral. The service neutral carries the unbalanced current between these two hot conductors. So lets call one leg A and one Leg B. If leg A is carrying 20 amps and leg B is carrying 25 amps then only 5 amps actually returns to the center tap of the transformer on the service neutral....the unbalanced current. The fact that the legs are 180 degrees shifted at the source (transformer) results in all current but the unbalanced current to cancel on the neutral. So if you had 20 amps on leg A and 20 amps on leg B you will have zero current on the "neutral" as it serves to carry only the unbalanced current between the two hot wires of the service drop to your home. 20 - 20 = 0 current. take a look at this example diagram of a 3 wire service entrance. Study it some and if you like come back ask questions. Notice that at the transformer there is 120 volts potential from each leg to neutral and 240 volts from leg A to leg B. This is because we tap the winding at the center point between the legs and this results in zero as noted by the + and - at each end of the winding of the transformer. The loads #1 and #2 represent the buses in your main panel that your branch circuits are connected to for you homes electrical needs.



And a typical dryer or range branch circuit with a neutral. The 240 volt needs of the appliance do not require a neutral so all current travels on leg A and Leg B. But Leg A is tapped to supply the 120 volt needs of the dryer or range and carries that unbalanced amperage on the neutral. So this 3 wire branch circuit has a "neutral" serving the unbalanced current between two hot wires. The box with the breakers represents a double pole breaker connected to both buses of your electrical distribution panel.



And a diagram showing a grounded leg branch circuit (not a neutral). The white wire serves to carry the current of only one ungrounded (hot) wire.

 

Last edited by Bruto; 09-20-08 at 12:17 PM. Reason: added range/dryer branch circuit
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Old 09-21-08, 03:08 AM
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Originally Posted by Tolyn Ironhand View Post
ALL grounded conducters originate in the transformer and have nothing to do with the ground rod. *note I'm talking about the grounded conductor, not the grounding conductor* If you removed your grounding electrode conductor (the wire going from your service to your ground rod) from the ground rod and checked your voltage in the service you will find that nothing has changed. I know this because installing the ground rod is one of the last things we do when changing out a service.
The issue I was referring to isn't a change of voltage between the hot and neutral, it's a difference between the hot and ground. If your neutral has been grounded (and it is not a grounded conductor until you hook up that ground), then there is little to no voltage difference between any neutral anywhere and a nearby ground (like the metal conduit the wire is inside). If the neutral is not grounded, then there can be a significant voltage difference between neutral and ground (I've heard this called a floating neutral, used to be common in industrial facilities). Why does this matter?
Say you have 600V insulation on your wires. You have 480V between your hot and neutral, regardless. However, if you have a surge on the line, and your neutral floats to 150V between it and ground, your hot is now 630V above ground, and the wire insulation fails. Good way to cause a fire.

Everywhere I've ever been the ground gets hooked to a service first. It's certainly not safe practice to energize a panel before it's been grounded.
 
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Old 09-21-08, 08:27 AM
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As you can see in Bruno's first picture the neutral (grounded conductor) is grounded in the transformer. The service panel is then bonded by the bonding screw or strap to the neutral (grounded conductor) and therefore grounded. I was just pointing out that the ground rod really has nothing do to with the neutral and is part of the grounding system just like water pipe bonding.
 
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Old 09-21-08, 10:33 AM
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Everywhere I've ever been the ground gets hooked to a service first. It's certainly not safe practice to energize a panel before it's been grounded.
Installing a ground rod first will make no difference in safety. Nor will connecting to the water pipe. The system is grounded as Tolyn has stated. However it wouldn't be unsafe practice to connect the neutral first with the main bonding jumper installed if the wires are live.... but in most cases we are not, when working on the NEC side of the service, working live. Point being connecting the GEC system at the service equipment first does nothing for your safety.

Actually there is no return to the transformer thru you and earth if the system isn't connected to earth so it might be safer..... However we need stabilization of the secondary voltages by using the earth , and is one reason why we earth the transformer at the center tap. But once we earth the transformer we better have a effective ground fault path that is of lower impedance than earth or we get electrocuted when touching likely to be energized metal during a ground fault.
 

Last edited by Bruto; 09-21-08 at 11:51 AM.
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Old 09-21-08, 05:26 PM
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Originally Posted by Bruto View Post
Actually there is no return to the transformer thru you and earth if the system isn't connected to earth so it might be safer..... However we need stabilization of the secondary voltages by using the earth , and is one reason why we earth the transformer at the center tap. But once we earth the transformer we better have a effective ground fault path that is of lower impedance than earth or we get electrocuted when touching likely to be energized metal during a ground fault.
Funny, my boss has made this point to me many times. I guess great minds think alike.

BTW - Nice pictures. Where did you find them?
 
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Old 09-21-08, 06:45 PM
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BTW - Nice pictures. Where did you find them?
Hello Tolyn

The pictures are mine. Feel free to use them if you like. Seems appropriate if I'm going to have discussions I should be able to provide drawings that explain things the way I want. I'm not sure I fall into the great minds arena.......

Btw I have a son that lives in Minneapolis....Falcon Heights.
 
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Old 09-21-08, 08:40 PM
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Originally Posted by Bruto View Post
Hello Tolyn

The pictures are mine. Feel free to use them if you like. Seems appropriate if I'm going to have discussions I should be able to provide drawings that explain things the way I want. I'm not sure I fall into the great minds arena.......

Btw I have a son that lives in Minneapolis....Falcon Heights.
LOL! Nice, Thanks! A picture is worth a thousand words.
Small world! I live in Becker, Mn but, as you can guess, the job brings me all over the Twin Cites and out state.

BTW - You should add your location too. Just go to your account settings.
 
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Old 09-21-08, 08:59 PM
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BTW - You should add your location too. Just go to your account settings
.

Very well ..I'll do that....
 
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