Why Ground AND Neutral?


P

PVR

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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G

gfretwell

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.

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.
 
S

SQLit

PVR said:
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.
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.
 
T

TURTLE

PVR said:
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.
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
 
G

Goedjn

Simplified explanation
Ground is for a return path to the service to help with tripping the
breakers
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.
 
K

krw

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.
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.
 
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F

Frank Boettcher

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.
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.
 
R

Robert Barr

PVR said:
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.
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.
 
J

Jeff

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.
 
B

Beachcomber

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
 
B

Bill

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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P

Pat Coghlan

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
 
M

Murray Peterson

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

Goedjn

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
 
B

Bill

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.
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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Z

zxcvbob

Old_boat said:
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?)

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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