NEV (Neutral earth voltage)

Dsg319

Member
Location
West Virginia
Occupation
Journeyman Electrician
So recently I’ve been researching nev. and the effect it can cause on dairy farms. I realize anytime you have an egc connected to equipment it’s possible to be a 1-4volts difference between it and (remote earth). In what instances and installations does nev need to be a concerting matter? And can it be dangerous?
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
So recently I’ve been researching nev. and the effect it can cause on dairy farms. I realize anytime you have an egc connected to equipment it’s possible to be a 1-4volts difference between it and (remote earth). In what instances and installations does nev need to be a concerting matter? And can it be dangerous?
What is nev.? Neutral to earth voltage?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The connection of the EGC has nothing to do with the creation of NEV. NEV is simply a measurement of the voltage drop on the grounded conductor of the system. Typically it is applied to the voltage drop on the utility primary grounded conductor. One of the methods used to eliminate it on dairy farms is a neutral isolator. That device provides isolation between the primary and secondary grounded conductors.
 

Dsg319

Member
Location
West Virginia
Occupation
Journeyman Electrician
Say I created a voltage gradient, phase conductor directly earth. When measuring and keeping one lead at the exact spot of the fault, the further away you get, would voltage decrease or increase? From what I seen I believe it would decrease.
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
Say I created a voltage gradient, phase conductor directly earth. When measuring and keeping one lead at the exact spot of the fault, the further away you get, would voltage decrease or increase? From what I seen I believe it would decrease.
Guess it depends what you are referencing.

If the fault point is your reference then the further away you are from the fault the closer you are to "earth" potential.

If you are calling "earth" the reference then the closer you get to the fault the higher the voltage is to earth

The reason why cows can be more susceptible to those voltages is they have longer distance between their front and back feet than humans have between their two feet and therefore can span more voltage gradient in the surface in such situations. Then extend that max distance they can reach a little farther if they touch something with their mouth, plus they don't normally wear anything on their feet that may be at least a partial insulator.

The most common problems aren't a direct ungrounded conductor energizing something though, those are obvious problems and something is definitely failed in those cases. The more common but hard to explain (especially to non electrical persons) is the small voltages you find between true ground and items connected to the grounded conductor that will see a rise over ground that is equal to the voltage drop in the grounded conductor.

Simplified - if you have 120/240 center grounded supply, and a voltage drop of 2 volts between the source and the service equipment, there will be a measured voltage of 2 volts to earth on not only the service neutral conductor but also on the grounding electrode conductor and equipment grounding conductor, and everything else bonded to this point, so all your equipment that has any kind of connection to the EGC is sitting there at 2 volts to other non bonded earth potential surfaces, though nothing is wrong as far as NEC is concerned as a general rule.

Now go one step further and assume you have negligible VD on the service neutral but it is bonded to the POCO's MGN on their meduim volt distribution system and the MGN has a 2 volts rise above earth because of VD on the MGN. You will still see 2 volts on everything bonded to the neutral/EGC/GES and there isn't much you can do about it except the mentioned neutral blocker in another post or get POCO to solve their VD problem.
 
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