Basic question about ground and neutral in AC system

Thread Starter

Involute

Joined Mar 23, 2008
106
In a residential AC electrical system, loosely speaking, the circuit consists of the generator, the hot wire, the appliance, and the neutral wire completing the circuit back to the generator. The neutral wire is also connected to ground. How does current flow to/from the generator from/to the appliance over the neutral wire if the ground path is lower impedance? If the ground path isn’t lower impedance, how does it serve its intended safety function?
 

BobTPH

Joined Jun 5, 2013
2,721
The ground wire is not connected to the load, it is connected to the neutral wire only at the electrical panel. If current flows through the ground wire it is a fault. Outlets in dangerous places, like outside and in the kitchen and bathroom have ground fault interrupters. which shut off the circuit if current flows in the ground wire.

Bon
 

dl324

Joined Mar 30, 2015
12,210
The neutral wire is also connected to ground. How does current flow to/from the generator from/to the appliance over the neutral wire if the ground path is lower impedance? If the ground path isn’t lower impedance, how does it serve its intended safety function?
In the US, neutral is only connected to earth ground at the circuit panel, so it carries current back to the panel.
 

MrChips

Joined Oct 2, 2009
22,468
There should be no current flowing in the GROUND wire.
There should be no connection between NEUTRAL and GROUND at the load. They are connected at the distribution panel.
 

MaxHeadRoom

Joined Jul 18, 2013
21,962
A neutral is an arbitrary designated conductor that when connected to earth ground, becomes a neutral.
A earth ground path IS a low impedance (or should be) path from source to end usage circuits.
Here is an instrument that measure this value, which in many jurisdictions should be 2.5ohms or less from end use to ground source.
Max.
 

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Thread Starter

Involute

Joined Mar 23, 2008
106
I don’t have the ability to make a drawing at the moment, so bear with me. On one half-cycle, current flows from the generator, into the panel on the hot wire, through the load, back to the panel on the neutral wire, then back to the generator. If the neutral wire is connected to ground at the panel, why does the current “choose” to flow to the generator and not to ground, the lower impedance path?
 

andrewmm

Joined Feb 25, 2011
874
I tend to think of these as a two wire system, A and B,
at the generator, a voltage is generated, which cycles between the A being more +ve than B, and goes through B being more positive than A , In a sine wave.

At the far end, the house, we see A +ve to B, going so that B is more positive than A.

All well and good.

Now to confuse things,
lets connect at the generator the B line into the ground,
so now A moves above and below B.
at the receiver, the house, does this matter ?
we still see the same voltage between A and B.

Call A live, and B negative, and the world is happy,

Ground, is normally called safety ground,
its there, so that any metal around the house, has a route to ground, such that if its wrongly connected to A ( live ) then current will flow to the ground, not through any person that touches it , and hopefuly blows the fuse / trips the trip.
 

crutschow

Joined Mar 14, 2008
25,980
If the neutral wire is connected to ground at the panel, why does the current “choose” to flow to the generator and not to ground, the lower impedance path?
It doesn't "choose".
It doesn't flow because there is no complete ground path for the current to flow.
Neutral is connected to ground at only one point (connection) at the panel.
For current to flow it needs two connections (complete path).
 

Thread Starter

Involute

Joined Mar 23, 2008
106
It doesn't "choose".
It doesn't flow because there is no complete ground path for the current to flow.
Neutral is connected to ground at only one point (connection) at the panel.
For current to flow it needs two connections (complete path).
So, if current can't flow from neutral to ground, what purpose does the ground connection serve? High-level diagrams of the generation and distribution system often show the generator also connected to ground, allowing a return path between the consumer and the generator, literally, through the ground, though I've always been skeptical of this, given the resistance of tens of miles of earth. But I digress.
 

MaxHeadRoom

Joined Jul 18, 2013
21,962
As per my post in #15.
GND is normally finally connected at the distribution panel, but should not contact the neutral anywhere else in the distribution system wireing or appliances etc.
It is also connected at the source neutral.
Max
 

crutschow

Joined Mar 14, 2008
25,980
if current can't flow from neutral to ground, what purpose does the ground connection serve?
To drain off any stray charges and maintain the AC common-mode voltage at ground potential.
Otherwise it could drift to a high voltage due to stray static charges or mains transformer leakage and damage anything connected to the mains in your house.
 
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