Why Ground AND Neutral?

In my new condo at the breaker box I note that Neutral and Ground wires from the house side are connected to the SAME bus. Why is this? Why not have just one of these at the controlled device? I'm assuming that this is a kind of fail safe arrangement?
Peter.
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from
just
Grounds and neutrals are supposed to be connected at the service. Separated everywhere else. If your breaker box is the service then all is well. If the box is a sub panel then call the local authorities and have them look at it.
Simplified explanation Ground is for a return path to the service to help with tripping the breakers Neutral is a grounded conductor for 120v loads.
Have one wire do both jobs has been proven to be unsafe.
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I thought that the primary purpose of the equipment/safety ground was to provide a path to ground with lower impedance than you. The fact that it also trips the breaker when you get a short to the equipment casing is just a bonus.

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You're right. That's why everything conductive (except for the power circuit) on a grounded device is tied together and tied by good path to ground.
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snipped-for-privacy@mail.uri.edu says...

There are many reasons they're separated. One biggie; if the neutral opens, the grounds still remain at ground potential. The neutral (downstream of the break) won't. If the ground and neutral are connected together downstream of the open neutral, the grounds are now energized. ...not good.

Ok, but this will confuse more people than it will help. It may be the "grounded conductor", but it is *NOT* ground.
--
Keith


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Yep, the two need to be connected at the main panel, so that if there is a short to the ground wire, it will trip the breaker.
And yes, the whole idea of grounds and grounding is for safety.
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This is Turtle.
Well Peter it all goes back to when I was a kid in the HVAC / R business and when a customer in a Grocery store had a reach in cooler that was shocking the customers when they touched it. They would just turn the plug over and the shocking would go away. Now when you did this you had a hot wire touching the shell of the cooler and if the ground wire was ever broken or become loose. it would put 120 volts on the shell of the cooler and kill someone because unlike the first shocking deal. This was a full 120 volt going to you and the old deal it would not very much of a charge to hit you.
Then the NEC came up with the good ideal of having a Appliance ground and a Operation Neutral to run the cooler on. Then when the cooler had a short to gropund it would trip the breaker or fuse all the time and make you go fix the cooler correctly like you should have in the first place. Now a day if any power goes to the shell of the appliance it will trip the break in all cases and you will have to fix it if you wanted it to work.
Thus came the seperate Ground wire and the Seperate Neutral. You can combine the neutral and the Ground wire but only at the point where the electric service leaves to the electric service leaves the building to go back to the electric service from the line service.
TURTLE
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On Wed, 21 Sep 2005 11:12:05 -0400, "PVR"

That is probably wrong in a condo. The only place they can be connected to the same bus is at the service disconnect where the ground electrode connects. The neutral carries current and will not be "ground" potential as soon as you start getting away from the ground electrode.
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PVR wrote:

The neutral is designed to carry current. The ground keeps the chassis at zero potential.
Because there will be some resistance in the wiring, the neutral at the appliance (or whatever) won't be at zero potential -- it will be at IxR. This will normally be very low, but it's not zero.
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In the past many tools and appliances had metal cases and they would have a ground wire connected to the case so that if the hot lead shorted to the case it would trip the breaker and not shock the user. Well you might say just connect the neutral to the case and use a polarized plug. Obviously if the plug is reversed you get shocked or even the neutral is broken, say in the power cord, then the case is connected to hot through the motor windings etc.
Now we have plastic cases so this is less necessary but still important with appliances such as washers and dryers.
Reminds me when I was visiting a friend's new house and checking out the basement. I noticed the electrical service was grounded to the water pipe nearby. But the water came into the house in heavy plastic pipe. Friend called and they put a copper stake in the ground and grounded the electrical to it.
This is important where we live because of lightning which often hits power lines.

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One further advantage of modern grounding that may not be so obvious.
In addition to lightning protection, a properly grounded installation offers protection if the primary hot wires of your distribution transformer should accidently come in contact with the transformer secondary service drop to your house.
For example lets say the primary voltage to ground is 7500 volts and a storm blows this wire onto your 240/120 service drop conductors. Most likely, a fuse, (ahead of the transformer in the primary) will blow shutting off the current (because of the short or near short to ground). Even if this doesn't happen, with a grounded system, the stray voltage coming into your house will probably be a lot more than 240 volts, but also, probably a lot less than 7500 volts.
Beachcomber
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An electrical appliance with a metal case can "malfunction" and cause the metal case to become "energized".
To prevent you from being electrocuited in this situation, the metal case is "grounded" using a separate ground wire.
Now if you were to instead use the neutral wire for grounding, and then the neutral wire came loose anywhere between the appliance and the breaker panel, and then you "turned on" the appliance, the metal case would then become "energized' as the hot wire current would travel from the hot wire, through the switch, to the neutral wire, then back up through the ground wire to the metal case.
Turning on the appliance switch would have the effect of connecting the metal case of the appliance to the hot wire in this situation!
So *always* use a separate ground wire - never connect a ground to neutral (except at the panel of course).
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This is a multi-part message in MIME format. --------------000504070604070006070207 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit
On a hydro pole, there are always 3 wires...at least in Canada. The 3rd wire is neutral, going back to the substation, isn't it?
Why is that 3rd wire there if neutral is simply tied to ground at the panel. This would seem to obviate the need for that 3rd transmission wire.
-Pat
Bill wrote:

--------------000504070604070006070207 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body bgcolor="#ffffcc" text="#000000"> On a hydro pole, there are always 3 wires...at least in Canada.&nbsp; The 3rd wire is neutral, going back to the substation, isn't it?<br> <br> Why is that 3rd wire there if neutral is simply tied to ground at the panel.&nbsp; This would seem to obviate the need for that 3rd transmission wire.<br> <br> -Pat<br> <br> Bill wrote:
<pre wrap="">An electrical appliance with a metal case can "malfunction" and cause the metal case to become "energized".
To prevent you from being electrocuited in this situation, the metal case is "grounded" using a separate ground wire.
Now if you were to instead use the neutral wire for grounding, and then the neutral wire came loose anywhere between the appliance and the breaker panel, and then you "turned on" the appliance, the metal case would then become "energized' as the hot wire current would travel from the hot wire, through the switch, to the neutral wire, then back up through the ground wire to the metal case.
Turning on the appliance switch would have the effect of connecting the metal case of the appliance to the hot wire in this situation!
So *always* use a separate ground wire - never connect a ground to neutral (except at the panel of course).
</pre> </blockquote> <br> </body> </html>
--------------000504070604070006070207--
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"Pat Coghlan" wrote in message

wire is neutral, going back to the substation, isn't it?

wire.
I don't know about Canada, but in the U.S....
-For a home there will be 3 wires - two hots and a neutral. -At the top of the electric pole will be 3 wires - 3 hots - 3 phase. -Sometimes lower on the pole will be 3 wires - two hots and a neutral. -For businesses there may be 4 wires - 3 hots (3 phase) and a neutral. Then this gets *very* complicated as to what the 4 wires are for depending on the transformer and how it is wired. See following... http://www.federalpacific.com/university/transbasics/chapter3.html
3 phase makes large electric motors run more efficiently basically. Homes are usually connected to single phase.
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So if you are putting a new outlet in an old house that used to have non grounded outlets, what is the acceptable method for hooking up the new grounded outlet as you cannot buy the non grounded ones anymore and are not running new grounded cable.
1. Just Not hook up the ground?
2. Hook up the ground to the neutral ( is this better than 1?)

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Old_boat wrote:

You *can* still buy ungrounded outlets. You just have to look for them, and they may cost you $2 when a grounded outlet just like it is 50.
Or you can install a GFCI outlet and put on the little sticker that comes with it that says "No Equipment Ground".
Or you can run a separate ground wire back to the main panel or to any accessable point on the grounding electrode conductor. You used to could run this wire to a cold water pipe, but not anymore (and it never was a very good idea.)
Best regards, Bob
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wrote:

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No, the third wire is not a neutral. The power is distributed as three phase, with all three lines supplying current.
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