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Old 04-27-2008, 06:28 PM   #16
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3 wire to 4 wire question


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Originally Posted by BigJimmy View Post
Nice to see you back, Andy!
Jimmy, that post from andy was from nov, 07
I don't know if he is coming back.
I hope him and Honker are ok!

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Old 04-27-2008, 07:52 PM   #17
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3 wire to 4 wire question


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Jimmy, that post from andy was from nov, 07
I don't know if he is coming back.
I hope him and Honker are ok!
Dang! Sorry I didn't notice. Dunno how I did that!
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Old 04-27-2008, 09:56 PM   #18
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3 wire to 4 wire question


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Originally Posted by elliowb View Post
Thanks a lot jrclen. I've changed out switches, fixtures, and even added new circuits with no problems. Situations like this though, tell me how little I really know about electricity.

-- Bill
I understand Bill. I hope you are cleared up now. Any more questions just ask. We are all happy to help. Questions are much better then mistakes in electrical work.
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Old 04-30-2008, 12:29 AM   #19
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3 wire to 4 wire question


Hi jrclen,

Just so I have a better understanding, let me ask you one more thing if you don't mind. I've been trying to understand exactly how the electricity flows in my cooktop. In reading about the grounding conductor and a grounded neutral, I found the following on Wikipedia:

"While a neutral wire is always "grounded", it should not be confused with the electrical system's "equipment grounding conductor", which is not intended to carry any electric current during normal operation, but serves to do so in the event of a "fault", which is the unintentional imposition of current, such as during a "short circuit" or "ground fault"."

What's confusing me is if the grounding conductor (in my case the metal conduit) is not ordinarily supposed to carry any current, why doesn't my cooktop have any means to return the current. The conclusion that I'm finally coming to is that the current flows between the two hot wires (and that's what makes it 240 rather than 120) and that's why a neutral isn't necessary. And the ground still only carries current if there is a fault in the normal circuit. Is that correct?

-- Bill
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Old 04-30-2008, 01:10 AM   #20
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3 wire to 4 wire question


Hello Bill

Yep, you got it pretty well figured correctly. But lets clarify a few things first.
It's all about terminology. We have as a matter of convenience used the term 'Neutral' to describe the grounded conductor (usually white) of a 120 volt circuit. This is actually not correct, in a two wire circuit with equipment ground the white is simply a grounded leg meaning when it gets back to the service equipment it bonds with the service NEUTRAL. However it carries all of the return current of the branch circuit. A neutral does not. It carries the unbalanced current between two or more hot wires. An example would be a free standing range that has an oven and cook top burners. The nameplate on a range will state 120/240 volt appliance, meaning it needs 120 volts and 240 volts to operate properly. So we have 2 hot wires and a grounded leg. Only the grounded leg of a range is a neutral which carries the unbalanced load between its 2 hot wires. A kitchen aid mixer is strictly 120 volts and therefore has a grounded leg that carries all return current of the appliance coming from one hot wire.

Your cooktop is strictly 240 volts and therefore there is no grounded leg or neutral, just two hot wires and the equipment ground. No wire is brought back to the service neutral (the utility grounded conductor) and bonded to it making that wire a grounded conductor.

You are absolutely correct the current just flows in a loop as it alternates direction from the endpoints of the utility transformer winding. See the image below. Click on it to enlarge. Notice there is no connection to the grounded leg (aka neutral) on the 240 volt load. Also notice there is 240 volts potential between Leg A and Leg B with respect to each other at the transformer winding. You also see there is 120 volts of potential between Leg A and the grounded leg which is connected to the center of the transformer winding. The midpiont between legs or center of the winding is designated 0 volts with respect to earth potential.
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3 wire to 4 wire question-120-vs-240-volt.jpg  

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Old 04-30-2008, 01:25 AM   #21
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3 wire to 4 wire question


Thanks a lot Stubbie. I don't know why it took me so long to come to that conclusion, but I really appreciate your confirming my thoughts and giving me more detail. The diagram makes perfect sense.

I'll definitely sleep better!

-- Bill
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Old 04-30-2008, 08:42 AM   #22
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3 wire to 4 wire question


Bill, I knew Stubbie would come along with one if his great explanations and pictures.

I'd like to add 2 cents worth. Your two wires for 240 volts are opposite polarity. Picture 1 positive and 1 negative. So the electrical current flows from one to the other. Being AC power, the current reverses 60 times per second. So as Stubbie said, no neutral or grounded conductor is needed for this circuit. A voltmeter placed across those two wires will read 240 volts.

The grounding conductor, also called an equipment grounding conductor is a safety. If one of the ungrounded conductors above short circuits to ground (a ground fault), the equipment grounding conductor (your conduit) carries that current back to your electric panel and then on out to the transformer where the power comes from. That high current flow will cause a high current flow on one of the "hot" wires, which causes the circuit breaker or fuse to open and kill the power. It does this very quickly if we provide a low impedance (resistance) path for that fault current. That path can be the conduit or a grounding conductor (wire). The key point is the path going back to the source of the power, the transformer, not to the earth as many people believe.

Another type of short circuit would be for those two wires for your 240 volts to touch each other. This would be a leg to leg or bar to bar fault and again would result in very high current flow which of course would open the fuse or circuit breaker once again to protect the circuit and yourself.
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Old 04-30-2008, 11:55 PM   #23
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3 wire to 4 wire question


Hi John,

Thanks for the additional information. I always like to know the 'why' of what I'm doing. What was causing me a problem in understanding the 240v circuit, was that I kept thinking that the hots had to have a return neutral and that 'somehow' the two of them together added up to 240v. I realize now that that was bad thinking because you need that total difference in potential of 240v or you need a transformer.

I guess a good analogy would be that in a regular 120v house circuit, as the current alternates, it first pushes and then pulls. While in a 240v circuit, the one leg pushes while the other leg is pulling and then they reverse roles.

Thanks again,

-- Bill
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Old 05-01-2008, 02:27 AM   #24
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3 wire to 4 wire question


Stubbie . . .nice of you to help a fella

?...I didnt see where the Lad told us what COLOR his leads were? . .just
out of curiousity

? . .arent some of the newer appliance internally bonded neutral /
ground . . . .doesnt the code allow that in some circumstances?

I always like to hear the fellas tell us what color leads as
well . . .and pictures are great as well


thanks again
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Old 05-01-2008, 05:34 AM   #25
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3 wire to 4 wire question


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? . .arent some of the newer appliance internally bonded neutral /
ground . . . .doesnt the code allow that in some circumstances?
All new 120/240v appliances come from the factory with the neutral bonded.
It is up to the installer to leave or remove this bond according to the type of cord they are installing. The receptacle dictates this.
All newer receptacles are 4-wire requiring a 4-wire cord and the neutral NOT bonded.

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Answers based on the 2008 & 2011 NEC.
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