Ground redundant with neutral?

Irving LaRue

Member
Location
Fairfax, Virginia
Occupation
Electrician Apprentice
I became an electrical apprentice about a year ago. My uncle, who has been a carpenter and handyman for over 40 years, had a dispute with me regarding the necessity of the grounding/ground/green wire in a circuit.

He insisted that the grounded/neutral/white conductor was sufficient to ground a circuit and the grounding wire wasn’t really necessary. He told me, “they both go back to the same place in the panel”. Of course, he’d hook it up where available, but didn’t see the need in re-wiring the house from wires without ground to newer wires with ground.

What is the difference between the function of the neutral wire and the ground wire? What function does the ground wire perform that isn’t present in a circuit with only a neutral and no ground? What changed in electrical circuits when the ground wire was added?

Thanks for the help!
 

Barney B

Senior Member
Location
Hurst, TX
Occupation
Electrical Instructor/Trainer
I became an electrical apprentice about a year ago. My uncle, who has been a carpenter and handyman for over 40 years, had a dispute with me regarding the necessity of the grounding/ground/green wire in a circuit.

He insisted that the grounded/neutral/white conductor was sufficient to ground a circuit and the grounding wire wasn’t really necessary. He told me, “they both go back to the same place in the panel”. Of course, he’d hook it up where available, but didn’t see the need in re-wiring the house from wires without ground to newer wires with ground.

What is the difference between the function of the neutral wire and the ground wire? What function does the ground wire perform that isn’t present in a circuit with only a neutral and no ground? What changed in electrical circuits when the ground wire was added?

Thanks for the help!
A "neutral" conductor (which the Code calls a grounded conductor) is a circuit conductor, meaning that it carries a portion of the load on the circuit under normal conditions. These are usually white or grey in color, but under certain limited conditions may be bare.
The "grounding" conductor (which the Code calls an equipment grounding conductor) carries no current under normal conditions. The function of this conductor is to provide a path for fault current to return to it's source quickly to allow the fuse or circuit breaker to trip quickly. These may be green, green with yellow stripes, or bare.
When grounding conductors were added to residential types of cables, the tripping speed of overcurrent protection devices was improved.

These two types of conductors do indeed have a common point of origin at the service equipment, but interconnecting them elsewhere is prohibited because of the safety hazards such connections can create.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
To some extent this is about relative safety rather than absolute safety.

In the past, the grounded circuit conductor was used to bond the frames of certain appliances.

Because the grounded circuit conductor carries current, this means that the frames of such appliances are at a small voltage relative to ground. Generally not a problem, but sometimes people will get shocked by this voltage.

Additionally, if the grounded circuit conductor fails open, then this could leave such a bonded frame at full line voltage.

Using a separate wire for bonding greatly improves both of these situations.

Going in the opposite direction (reduced safety but lower cost), my understanding is that in wartime Europe, the use of conduit as the grounded conductor was an accepted practice.

Jon
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
First read Barney and Winnie's posts. And then take Roger's advice when discussing electrical theory with non-electricians. The EGC and the neutral are not the same and using the EGC system is much safer than using a just neutral for equipment bonding and grounding.
 

Jpflex

Senior Member
Location
Victorville
Occupation
Electrician commercial and residential
The neutral or white INSULATED wire should connect to ground at one point Only at the first point of disconnect. You would think that if this being the case you would not need an additional ground wire since they lead to the same end point.

However this would work and be allowed to my knowledge if metalic boxes were used with EMT electric metalic tubing raceways all the way to panel with proper bonding jumper here. The Metal conductive conduit and metal gang box would take the place of the extra Ground wire. Therefore If a hot black wire hit the metal box, current would travel the metal emt conduit to breaker and trip.

However if using NM non metalic cable common with house wiring and eliminating ground wire then if the metal box touched hot black wire, the current would not be able to travel the Non conductive jacket of NM cable (Romex) as it would with EMT raceway explained before. This poses a shock hazard

So it depends on wiring setup
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
221001-2143 EDT

Many persons looking at electrical circuits do not adequately think about the problem.

So consider a 100 ft piece of Romex with #14 copper wire for each of the conductors. Also consider that 5 mA is sufficient current to give a substantial shock that might even cause you to fall off a ladder. Also assume that all water pipes, gas pipes, and other conductive elements are at very close to the potential of the electrical system at the main grounding point at the main panel.

Now put a short between hot and neutral at the end of the 100 ft cable. This does not change the potential of the EGC. So if you touch the EGC and any non current carrying conductor attached to the electrical grounding point, then you will not get a shock, no potential. But within a washing machine or other device you could have up to about 1/2 the source voltage. Only if the short is from hot to EGC will the EGC voltage rise.

There are certainly a reasonably number of faults that don't go to the EGC. and therefore a person never feels a shock from such a fault.

I could provide other cases, but this example provides a good illustration of the best that can be achieved.

.
 

Jpflex

Senior Member
Location
Victorville
Occupation
Electrician commercial and residential
To some extent this is about relative safety rather than absolute safety.

In the past, the grounded circuit conductor was used to bond the frames of certain appliances.

Because the grounded circuit conductor carries current, this means that the frames of such appliances are at a small voltage relative to ground. Generally not a problem, but sometimes people will get shocked by this voltage.

Additionally, if the grounded circuit conductor fails open, then this could leave such a bonded frame at full line voltage.

Using a separate wire for bonding greatly improves both of these situations.

Going in the opposite direction (reduced safety but lower cost), my understanding is that in wartime Europe, the use of conduit as the grounded conductor was an accepted practice.

Jon
When you said in the past, some appliances had their frames bonded to the grounded circuit conductor how would there be current on these, unless tied in with a neutral?

Also I’ve always wondered why neutral doesn’t have full voltage potential on alternate ac cycles as it does on the line side prior to load. If current cycles both polarities in ac systems It would seem like the black and White neutral would take turns being the “line hot” per consecutive cycles.

In dc all voltage is consumed after the last load so I assume it’s similar to ac but with polarity shifting.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
When you said in the past, some appliances had their frames bonded to the grounded circuit conductor how would there be current on these, unless tied in with a neutral?
The grounded conductor is the neutral in this discussion.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
When you said in the past, some appliances had their frames bonded to the grounded circuit conductor how would there be current on these, unless tied in with a neutral?

Also I’ve always wondered why neutral doesn’t have full voltage potential on alternate ac cycles as it does on the line side prior to load. If current cycles both polarities in ac systems It would seem like the black and White neutral would take turns being the “line hot” per consecutive cycles.

In dc all voltage is consumed after the last load so I assume it’s similar to ac but with polarity shifting.

The 'grounded circuit conductor' is usually, but not always, the 'neutral'. It is the conductor that carries load current (circuit conductor) that is connected to the earth electrode (grounded).

A 'grounded' electrical system is one which has a single terminal connected to 'earth'. If that electrical system has a neutral, then code requires that the neutral terminal be the one that gets grounded. Thus for _most_ systems the 'grounded conductor' is also the 'neutral conductor'. But you can have an electrical system that doesn't have a neutral, and still ground it by connecting one (and only one!) of the non-neutral terminals to ground.

For example, you can have a 'corner grounded delta' system where you have a transformer delta secondary, and you ground one of the 'phase conductors'. This is a perfectly fine grounded system, but it trips people up because one of the three 'phase conductors' reads 0V to ground.

As to the neutral not having full voltage every half cycle, this comes down to how voltage is defined. Voltage can only be defined and be measured between two points. A single point never has a voltage except by reference to something we define as 'zero'.

In a regular 120V circuit, the 'hot' wire is at 120V relative to the 'neutral' wire, and since this is an AC circuit, this is the same as saying that the 'neutral' wire is at 120V relative to the 'hot' wire. Because it is AC, sometimes the 'hot' wire is 170V + relative to the 'neutral', sometimes the 'neutral' is 170V+ relative to the 'hot', and they alternate 60x per second.

But since the neutral is connected to ground at the panel, when we make our measurements using the ground reference the voltage that we get is near zero. This is simply because we have a metallic conductor connecting the two points we are measuring between, the 'neutral' at the load and 'ground'.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
221015-849 EDT

jimport:

Back in the late 1940s I was sitting in the drivers seat on a hot humid night, and my skin was damp. With one bare arm on the driver's side door, and touching the horn ring with my other hand I could feel a little tingle. Car batteries in those days were 6 V. The horn ring was part of the horn switch. This was electrically hot thru the horn relay coil.

I don't know the threshold point in current when I start to feel an electrical current, but I believe it is noticeably below 1 mA.

If I have a piece of equipment with an EGC to earth or system grounding point, then it is possible that I could have amperes of current flowing to this grounded surface without a voltage rise high enough for me to feel the voltage ( current ) flowing thru that surface.

.
 
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