Neutral Wire Questions

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  #1  
Old 12-22-10, 09:01 PM
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Neutral Wire Questions

Okay...a few more ignorant questions to add to the pile.

1) If the neutral wire wasn't grounded, I assume that it would have the same 120 volt potential as the hot wire? (Thus the grounding is what makes the neutral wire, well, neutral).

2) If an outlet is in use, does the grounding matter at that point? (If I touched the "neutral" wire while in use, would I get a shock just the same as with the hot wire?)

Thanks...you pros inspire me.
 
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Old 12-23-10, 08:56 AM
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Originally Posted by JFS321 View Post
1) If the neutral wire wasn't grounded, I assume that it would have the same 120 volt potential as the hot wire? (Thus the grounding is what makes the neutral wire, well, neutral).
It would have a floating potential, but you can't know exactly what it would be. You could have a situation where the neutral floated up to 10V above ground which means hot would be 130V above ground. The potential between hot and neutral would remain 120V.

2) If an outlet is in use, does the grounding matter at that point? (If I touched the "neutral" wire while in use, would I get a shock just the same as with the hot wire?)
Yes the grounding still matters, and yes you could still get a shock from the neutral. It is usually not the same risk as a hot wire, but under the right (or wrong) circumstances a neutral can deliver a serious shock.
 
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Old 12-23-10, 11:01 AM
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So the neutral is not directly attached to one of the two hot supply lines coming into the house...?
 
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Old 12-23-10, 11:14 AM
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Originally Posted by JFS321 View Post
So the neutral is not directly attached to one of the two hot supply lines coming into the house...?
No. Your house is actually supplied with 240v from a center tapped transformer. From either leg of the 240v to the center tap is half the winding on the secondary, half the voltage, thus 120v. The neutral is the wire from the center tap. More correctly it is called the grounded conductor.

Some people have the mistaken idea that the 240 volts comes from two 120v supplies. It doesn't. The 240v is the power that is supplied to your house. The 120v come from using the center tap and one 240v leg.

All of the above applies to single phase power.
 
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Old 12-23-10, 11:19 AM
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No. The service from the power company is provided on three wires, hot-neutral-hot and the neutral is also grounded to the earth. The potential from either hot to the grounded neutral is 120V, the potential from hot to hot is 240V.

A simplified way of thinking about this is to imagine the grounded neutral at 0V, one of the hots is +120V and the other hot is -120V. Each is 120V from the ground, but 240V from each other. In reality A/C is more complex than that, but it is conceptually valid.

Hot |<----- 120V ----->| Neutral |<----- 120V ----->| Hot

In most electrical systems (all residential systems) the neutral is connected to the earth to provide some safety as it reduces the possibility of being shocked.
 
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Old 12-23-10, 09:32 PM
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Here's my attempt at explaining the neutral. please pardon my artistry.




Here's a transformer, like the one coming from your power company to your home's breaker panel. If you look at your lines atop your house, you will see 3 wires coming in (two hots and a neutral). Sometimes there's 4 wires, which contains the ground wire. This is another topic.

Between points A & B in the first image, there will be 240v. note that this is a two wire system, providing only 240v, and ther's no neutral.

In the second image, again between a & b, there's 240v, but between either a & c or b & c, there's 120v.

"C" is the center tap (exactly center in the transformer windings) providing a point for 120v. If the center tap wire were to be located closer to point "a", then a different (lower) potential could be read between points "a" and "c". Likewise, a different (higher) potential would be found between "c" and "b".
 
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