AC grounding questions

The purpose of having grounding pin on AC outlet is to ground metalic surfaces of appliances so that there can be no voltage to hurt anyone even if there is a leak. Right?
If an AC outlet has the ground and neutral reversed, would it cause any problem? If an AC outlet has no grounding wire (old house) and instead the ground prong is connected to the neutral, would that cause any problem?
Is neutral connected to ground at the circult breaker panel?
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Right.
If the neutral is shared with another outlet, there is the very real possibility of voltage being on it.

Yes, then the metal surfaces of the appliance would be subject to voltage.

Yes, but that does not mean they are interchangeable in usage at the outlet end. It is to insure that the breakers trip if the hot line is shorted out to ground and not just the other side of the power line.
-- If I had something witty to say, this is where I'd say it.
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wrote:

I remember taking awhile to understand the difference between neutral and ground (connected at the panel). Neutral can be at a different voltage because of current on it. The ground wire normally doesn't carry current and should be at 0V.
Also, it's unsafe to have ground connected to other receptacle(s) but not the panel (as someone who thinks a GFCI actually provides ground might do).
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Yes, you are putting circuit current on the ground.

What happens if someone got the polarity reversed in a box upstream? You just put 120v on the case of your equipment and a circuit testeer would still say everything was fine.

Only at the service disconnect. Anywhere down stream of that will show a voltage rise on the neutral, equal to the voltage drop in the hot conductors.
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wrote:

To be more specific, when you return current to the utility via the neutral conductor, there will be a voltage drop along that path proportional to the resistance of that conductor. If a failure or resistive connection develops, that voltage could be quite high (closer to the hot V).
This voltage drop on the neutral is expected and most electricians will avoid touching the white wire as well as the black. The ground (AKA Safety Ground, not earth ground) is just a parallel connection which normally does not have much current flowing on it and thus does not have an expected voltage drop when a load is connected unless there is a leakage fault.
Much of the grounding system is not needed if everything is perfect but since things do fail, this is why it is here.

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I've seen in the codes something about window units having voltage leakage detectors on them. So many people have screwed with the ground wire in the past, they killed themselves adjusting the AC unit. Touch a unit, with an open neutral and a radiator, and get fried kind of stories I've heard.
So, I would get it fixed, reguardless if it works.
imho,
tom @ www.NoCostAds.com
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Besides what others mention you need to find out your houses efficiency, a Blower Door test is good it tells you how many air exchanges your house has and shows you where it leaks. Your attic is under insulated.
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Only at the main service panel - not at a subpanel... ...unless a grounding rod is required, as in a separate building, then the bonding screw is used at that subpanel.
Also, in the US, neutral grounds are sometimes legal, with major appliances on a dedicated circuit. Or at least they were. Existing 3 wire 120-240 circuits are still allowed to remain, but new construction requires a 4 wire connection to things like electric ranges and clothes dryers. No more neutral grounding allowed. I can't remember exactly when the NEC made these changes. I think it was 1996. Correct me if I'm wrong. Existing hookups are grandfathered, however, as long as there is no remodel/new construction.
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What would happen if (intentionally) the service didn't use a grounded neutral at all? Everything the same but don't ground the neutral at the transformer nor at the consumer's entrance panel. Would that make things more dangerous or reduce shock hazard because you could only get a shock if you bridged two conductors?
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On Thu, 29 Jun 2006 04:23:25 GMT, Steve Kraus

You lose the hazard of the first line to ground fault but you lose the control of what that line to ground voltage might be. It would also make your electronics more easily damaged by lightning.
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On Thu, 29 Jun 2006 01:16:32 -0400, snipped-for-privacy@aol.com wrote:

Lightning? Hardly.
When lightning zaps a circuit, it flows common-mode, down all three conductors. It WILL find a path to ground.
Six million volts is brutal by nature. <g>
A few hundred gigawatts doesn't take very long to toast anything in its path.
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-john
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The danger would be that the voltage to ground would be uncontrolled. Any leakage or accidental connection from the transformer primary could raise both sides of the house wiring to the primary voltage, which could be several thousand volts. Definitely more dangerous.
Don Young
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