Electrical Grounding 101

ELECTRICAL GROUNDING 101, THE VERY BASICS

I’ve never seen so much confusion in my life as lately posted on these boards regarding Neutral and Grounds and Grounding when it comes to our typical home and shop 120/240 volt single phase 3 wire services, so I will try me best to educate yall in hopes to keep you safe. It’s IMPOSSIBLE to convey an a few paragraphs what I spent much of a lifetime in learning (and what can fill books) when I practiced as a secondary power distribution engineer and it’s been years since I retired and I’m a lil rusty, but I will give it my best shot.

1) NEUTRAL: The neutral is a GROUNDED CONDUCTOR. Its carrys current PLUS at the service entrance panel its bonded to the Equipment Ground Buss, soooooooo it’s a “Grounded Conductor”.
2) The Neutral is tied to the center mid point of a 240 volt transformer and that’s how you get two legs of 120 volts (L1 to N and L2 to N) service PLUS 240 volts (L1 to L2)
3) If all loads were perfectly balanced and there was the exact same current draws on L1 as L2 there wouldn’t be any neutral current, however, if not (as typical) the Neutral also carries that imbalance current .
4) GROUNDING: Actually what gets grounded BOTH at the outdoor utility transformers secondary and your service entrance, be it up on the riser or the meter base or the main panel, IS THE NEUTRAL. It gets bonded to mother earth (driven ground rods or metal water pipes etc) which is the best available single common zero volt reference plane. That way the grid and all the services and transformers etc all have a single common zero volt reference. Once more, the Neutral is grounded to mother earth on the utilitys high voltage primary (if it has a neutral) ,,,,,,,,,,on its secondary out at the pole or pad mount,,,,,,,,,,,,once more where it enters your home. IT’S THE NEUTRAL THAT NEEDS GROUNDED TO MOTHER EARTH NOTTTTTTTTTTTTTT ALL YOUR TOOLS AND APPLIANCES (they need to be tied to the equipment ground buss in your panel, see below)
5) ONCE AND ONLY ONCE at the main panel, the Neutral Buss is bonded to the Equipment Ground Buss. Those two big buss bars are tied together. You MUST NOT at other downstream sub panels in the building re bond N and G again. At a sub panel the N and G busses are separate and isolated, i.e. if you run to a sub panel you carry 4 wires, 2 hots, Neutral, Equipment Ground (and UNLIKE the main service entrance panel, the N and G busses are NOT tied together). The reason for all this is given a certain set of unfortunate circumstances like an open of one conductor yet a short at other places, it my be possible to energize the equipment ground buss system with live hot voltage and if you touch an appliance with a metal case (which is required to be tied to the Equipment Ground Buss) YOU CAN DIEEEEEEEEE
6) The sole purpose of the equipment ground (the bare/green wires) is to provide a dedicated low impedance return path for fault current back to the panel to clear a fault and trip the breaker so you don’t dieeeeeeeeeee if a hot phase conductor comes in contact (shorts out) with an appliances metal case. The bare/green equipment ground conductor MUST NOT BE USED AS A NEUTRAL nor rebounded to the N at any place downstream again from the main panel.
7) The safety DOES NOT come because you tie any appliance to any mother earth ground i.e. if you were to drive a rod in the ground and wire the appliance to it, that WOULD NOT carry sufficient return current to trip the breaker as the earth is a poor high resistance conductor. The safety comes because the appliance it tied to the bare/green equipment ground conductor, which happens to be tied to the N buss at the main panel so the equipment Ground Buss is the path for that fault current so the breaker trips to clear the fault and de energize the appliances case. THERES NO HELP OR SOLICE OR ADVANTAGE IF THE APPLIANCE IS GROUNDED TO MOTHER EARTH, It needs bonded to the equipment ground to trip the breaker and save your life, grounding to mother earth is no help, you can still dieeeeeeeee if that’s the ONLY path for fault current back to the panel, its high resistance and the breaker don’t trip.
8) ONCE MORE it’s the Neutral that gets tied to mother earth, at the transformer and your service entrance, that has NOTHING to do with the Equipment Ground Buss. Even if the Neutral was NOT tied to mother earth, yet at the panel the N and G busses were properly bonded and there’s a short form L1 or L2 to to an appliance case, the equipment Ground Buss saves your life by tripping the breaker NOT BECAUSE OF ANY BOND OR NON BOND TO MOTHER EARTH ANYWHERE…The appliance case bonded to mother earth only dont help you if theres a shot of a live conductor to the appliance metal case……What saves your life is the appliance bonded to the equipment ground system REGARDLES OF ANY GROUND RODS OR CONNECTIONS FROM THE APPLIANCE TO MOTHER EARTH AND REGARDLESS IF N IS TIED TO EARTH

In closing longggggggg ago before I understood all this I thought like many here, “Hey at the Panel the N and G are tied together, whats all the fuss and difference, they’re basically the same” BUTTTTTTTTT in years of practice and taking NEC courses from the likes of McPartland and Holt I’ve learned these NEC rules are wellllllllll thought and reasoned out by experts and there’s darn good reasons why there are in place regardless if a lay person don’t understand why THEY ARE THERE TO AND WILL INDEED SAVE YOUR LIFE OR PREVENT A FIRE.

God Bless n keep yall safe and although the atheist and secular humanists cant stand this, I wanna say Merry Christmas, it’s a celebration of the birth of Jesus Christ and despite their objections, it even happens to be a Federal Holiday……………

John “T “ Nordhoff from Indiana

That was very informative, I think. I wish I could absorb all that. But the last paragraph was the best one. Even I got it. Thanks for trying to educate us. Merry Christmas to you too. TDF

Very good...

Wondering though.. My place has a main breaker panel out by the meter that feeds 3 buildings.. None of the circuits going to the buildings have a ground conductor.. All are 3 wire.. Each building has it's own ground rod..

From what you said this is a no-no but wondering if it was ever OK as it was wired this way when we bought the place. At some point I have to assume it passed someone's inspection.

Would be a major ordeal to change it as two of the drops are direct burial with just enough conduit to get under the ground. Wouldn't care for the idea of replacing about 500 feet of buried hi-dollar wire.. Suppose I could just bury a ground wire but even that would be a big risk I might run into the existing drop with the trencher.. It will probably just get left as it is and hope...

This used to be standard practice--each building was treated as a separate service from a grounding standpoint. In other words we ran a neutral and two "hot" conductors from the main service to the outbuilding, installed a ground rod and bonded the neutral and the equipment ground at the outbuilding service. The code was changed some years ago to require running a separate equipment ground from the main service to each outbuilding. As with most if not all code changes existing installations are grandfathered and don't need to be changed. As long as you have a good ground at each outbuilding you should be OK.
Paul

Farm wiring code as it applies to separate buildings and grounds is different and not the same as residential code. I mention only since this is a tractor, and farm-related forum.

I'll also add that National Electric Code is a "suggestion", it is NOT the law. It's your state and/or local county government, or sometimes the city, that can take some of it, all of it, etc. and make it law.

Well said John,

After having read some of the threads yesterday and today I've concluded that many of the forum members must have stayed at a Holiday Inn recently!

Electricity should be respected.............AND perhaps even somewhat feared if you have no education regarding the subject.............YET for some reason that doesn't stop people from expounding their completely UNEDUCATED and DANGEROUS opinions...............

It seems like some people feel that if they've installed a receptacle in their garage or kitchen they consider themselves properly educated on the subject of electricity.........

In many cases there are more that one way to "skin the cat" but is regards to electricity, specifically high voltage electricity, "skinning the cat" the wrong way will result in the consumption of all nine lives!

Happy HO HO to you and yours,

Glen

Let me re-emphasize what John T. has said. The neutral is a "grounded" conductor and is allowed to carry current under normal conditions. It is referenced to "ground" at one point only.

The "grounding" conductor, also commonly know as the "green wire ground", "safety ground", or "fault protection ground" is not intended to carry current in normal operation. The "grounding" conductor is there to provide a low resistance path back to the power source ONLY IN THE EVENT OF A FAULT.

If you connect the neutral and ground wires at more than one physical point, then any current will split between the two conductors, negating the purpose of the fault protection conductor. Remember, circuit breakers and fuses take a finite amount of time to trip, and during this interval it is possible to have enough current flow to raise the neutral voltage to a level that can create a shock hazard. If you connect the safety ground to the neutral, you've negated the safety provided by the extra ground wire.

With regard to multiple distribution wires off the meter box not having ground wires, its common practice to treat each building as a separate distribution point and establish the neutral/ground connection separately for each building. Neutral is referenced to ground at the first panel in each building. As long as the power distribution systems in the buildings are never connected together between buildings, everything is fine.

Keep in mind that the resistance of a ground rod to physical earth is typically measured in the 10's of ohms. A short from the hot side of the power system to earth, or something in contact with earth, can carry plenty of current to kill, but no where near enough to trip a breaker. Circuit breakers (and fuses) are protection against fire, the safety ground (or the use of double insulated load) is protection against shock.

Ground fault interrupters provide additional shock protection by sensing the leakage current to ground and rapidly opening the circuit.

While the NEC may be written as "guidelines", its because the originating organization is not a lawmaking body. However, in every jurisdiction I've ever heard of either the NEC or something similar is the law.

Remember, be safe and respect something that's capable of killing you in an instant. Codes are there for a reason, and most of them make good technical sense.

Keith

PS...one of my job responsibilities early in my career was designing power distribution wiring for large RF communications facilities, so I do have some hands on understanding of the rationale behind the code requirements.

OK then, silly question.

I have two outbuildings that have small panels in them that tie off the main panel in my house. Both of them only have one bus bus bar and it's directly attached (ie it's all one piece) to the neutral pole.

I've also got my ground running (running from the main panel) attached to that bus and all the ground running out to the various circuits.

I'm I reading this right in that I should have a separate bus for ground in the case that should not be bonded to neutral?

If so it seems kind of funny they would sell these boxes that way since they're small and almost always used as sub-panels.

Sorry if it's a stupid question, I kind of like electrical work and really like doing a neat, correct job.

K

Your's and others asking questions on how to make the system safest is far from being stupid.
Never seen a "modern" distribution panel without a separate ground and insulated neutral bar.
When the panel is used as a sub panel. The bonding screw between the ground bar and the neutral bar is to be backed off. Allowing the neutral to float due to voltage drop at it's normal .1 to 10V above true earth potential.
This the neutral system's tendency of raising the ground system above true earth potential.
Some sort of insulated/floating terminal block from any electrical supply house. Will bring those old remote panels up to par.
Nobody ever put in too many or too deep of ground rods/plates.

That is a sore point with one central service and several out buildings with their own distribution panels.
It becomes a problem with live stock in particular. Something raising the ground system above true earth in one building. Can cause tingle voltage in the same or another building. Even neighbour's buildings.
Anything that gets a ground and a neutral in a parallel path and the ground carrying neutral current is trouble.
With one central service and distribution panels in the outbuildings. At one time they required the ground and neutral bars be bonded together in the outbuildings and at the central service. This led to good intentions but bad voltages on anything "grouned".
The solution and a good one IF.......... each building has a very good grounding system. BUT.......few do. Is to back off the bonding screw at each remote panel between the neutral and ground bars. Now the neutrals can float up 0.1 to 10.0V above true earth potential. Without dragging the grounding system up with them.
The final approved solution around here is to pound ground rods and/or bury ground plates until there is a proven good grounding system.
The bond screw is not replaced between the out buildings neutral and ground bars.
A magnetic reactor called a tingle voltage filter is connected between the neutral bar and the ground system.
The neutral still floats unless there is a serious fault which brings the neutral above 10V above true earth. Then the tingle voltage filter starts to conduct and "clamps down" the errant neutral to "earth".

No, its NOT a stupid question, its indeed a GOOD WELL THOUGHT OUT QUESTION. Some panels are classified suitable for Service Entrance while others are NOT. This has to do in part with them having only one or two seperate busses and if its to be a sub panel in the same building IT CANT HAVE BUT ONE IT NEEDS TWO BUSSES THAT CAN BE SEPARATED. On service entrance dual buss panels, however, theres a bonding strip that can be used if its service entrance but the same would NOT be used if its a sub panel.

First of all, most of what I was talking about above refers to one building, outbuildings are treated somewhat different. Under prior NEC it was permissible to ONLY run 3 wires to an outbuilding, 2 hots and a Neutral IFFFFF theres no like phone lines or shared metal water pipe etc etc. BUT if there any shared conductive path like phone or water lines 4 wires were required and the N and G had to remain seperate and isolated just like any other sub panel in the same building. I believe in the new NEC 4 wires are ALWAYS required now i.e. those 3 wires to outbuildigns are no longer permissible.

Nowwwwwwwww before anyone jumps my stuff, hey 3 wires to outbuildings will work and its been done for years, Im just telling you that was when there wasnt and conductive path like phone or water lines between the buildings and Im just tellin what the NEC says and THEY ARE NOTTTTTT STUPID those rules can save your life or prevent a fire, do as yall wish, its your farm and life.

John T

Thanks for your input Keith, I always enjoy them and AGREE. While Im knee deep in theory its been years since I designed and Im rusty on the NEC so thanks for the post.........

John T

Bob, see my response to Kopec above, pretty much the same issue I think. 3 wires have been used and will work, but theres good reasons for the 4 when required, I wouldnt loose much sleep over it in the meantime but if you ever did a new installation Id recommend 4

John T

This is very good to keep on file for future work,if you would ever need it.
Copy and paste it onto word document and save it.

Phil

John T, some years back during an ice storm the ground wire (bottom line ) on the power line broke. This power line that was put in in 1948. Top wire I think has 7,200 volts. The top wire didn't break so we still had power. The bottom wire wasn't reconnected for 3 weeks.This break was up the road about 2 miles from me and from the break to the end of the line there were 8 homes and we all still had power.

Was operating like this dangerous? It appeared to me that we were operating off earth ground. Meaning ground rods at the houses and each pole had a copper wire that goes down the side of the pole into the earth. Your comments are welcome.

buickanddeere & John T,

Thank you. Now I know. It's kind of funny, I wired my house my self but had to have a licensed electrician come in and inspect it before I could get my insurance.

He saw one of those panels any never said anything.

The small panels I have (Square D Homeline, yes I know not the greatest but the main panel was a gift and I wanted to stick to the same thing after that) do have the bonding screws but they're not installed so the bar is "floating". Sounds like it's just a matter of adding a bonded bus and moving the grounds.

Thank you again, this has been very interesting.

K

John, thanks for trying to help us neophytes.
Couple questions.
Does a pvc plastic water line constitute another "conductive path" between outbuildings?
To simplify what NEC wants per above, (I know, it's not simple but complicated)
All bare grounds kept separated,.................. all neutrals kept separated and.......
are connected only by one screw or connector strip at the main box.

HMMMMMMM a typical 3 phase 4 wire Y HV primary service is 12470 Y 7200, They would have 7200 volts from line to neutral (which is tied to mother earth) and they could use one phase for a 7200 to grounded Neutral single phase run to your home. (all speculation so far mind you)

The 7200 volts is from Line to Neutral (which is tied to earth) so if you still had power the PRIMARYS Neutral current would have to have been flowing through the earth BUT DEPENDING ON MOISTURE AND DEPTH OF GROUND RODS AND SOILS MINERAL CONTECT ETC ETC pretty high resistacne and Id think the voltage would be lowwwwwwwww

Your Neutral was fine and your low voltage secondary line and current flow was NOT via earth but Id still expect since the primary voltage was low your secondary would have been low????? It all depedns on where the break was and the moisture and ground rods and mineral contect and remember at 7200 volts theres not near as much current flow required as in your 120/240 volt use.

Was it dangerous?? I say yes but not so much in your own home as out there around the utility lines........

I dont know everything lol but this is my best opinion

JT