Electrical Grounding

ELECTRICAL GROUNDING

Over the years on many many various Tractor Board postings concerning general home n farm AC wiring, I’ve observed a common misunderstanding regarding “grounding” n ground rods etc. which I hope to correct in the interest of safety education and am posting this all over the place.

First of all, it’s the service NEUTRAL that gets bonded to Mother Earth via made grounds like rods driven into the earth or metallic water or gas pipes etc. Out at the electrical pole the Neutrals (if a Y service) on the high voltage primary side are tied to Mother Earth,,,,, the Neutrals on the low voltage (120/240) secondary side of the transformer also get bonded to Mother Earth,,,,, ,,,and finally at the electrical service entrance meter base or the main service entrance panelboard or even up on the riser, its again the Neutral that gets tied to Mother Earth. That’s to keep the services n the grid etc. at one single common voltage reference which Mother Earth provides, albeit not perfect.

So what about the equipment safety ground, the bare/green GROUNDING conductor that is used on three wire appliances and is wired to the outer metal cases on an electric drill or skill saw etc., isn’t it “grounded” ??? Well, it is, but just because at the main service entrance the Neutral Buss and the Safety Equipment Ground Busses are bonded together, therefore, the safety equipment Ground is also tied to Mother earth but nottttt tt for reasons some might think. Since the Neutral conductor is an ordinary current conducting path which happens to be grounded, it’s referred to as a GROUNDED CONDUCTOR while the safety equipment ground (green/bare) is referred to as a GROUNDING CONDUCTOR. The sole purpose of the third wire safety equipment green/bare ground is not so that circuit is tied to Mother Earth n all those ground rods n water pipes, buttttt ttt it’s to provide a dedicated low impedance return current path back to the Neutral (Remember at the panel Neutral and Ground busses are bonded together) in case of a fault (like a hot wire gets shorted to the drill case) so the breaker trips de-energizing the circuit and you don’t die hanging onto the drill. I hear people talking about driving more ground rods and making sure that drill case or appliance or stove etc. is bonded to Mother Earth thinking that alone somehow makes it safe, while its NOT any bond to earth that can save their life, it’s the drill case or stove being bonded to Neutral back at the panel that’s critical. The safety equipment green/bare ground wire is tied to the drills case so if there’s short there’s a dedicated current return path back to the panel to trip the breaker. If you had a drill with a metal case and only a two wire circuit serving it with no third equipment grounding conductor and say you drove a ground rod and attached it to the drills case, you think that would save your life if a hot wire got shorted to the drill case NOOOOO OOOOO OOOOO OOO YOU DIEEEEE EEEEE. The reason is the earth (depends on moisture n mineral content etc. etc.) is a poor high resistance conductor so there wouldn’t be enough return current back to the panel to trip a 20 amp circuit breaker buttttt ttttt tt it only take like 50 milliamps through your old ticker to kill you which that short can continue to supply since there’s no low impedance return current path (like the equipment ground) to trip the breaker.

Sooooo ooo it’s the Neutrals that get tied to Mother Earth and driving rods into the earth to “ground” that equipment grounding conductor isn’t the thing, it’s the fact that it’s bonded to the Neutral and provides a current path back to the panel in case of a short/fault to trip the breaker n save your life that’s important.

Clear as mud lol John T Nordhoff, retired Electrical Engineer in Indiana

Dave, Same warning applies as my sub answer above to S. Crum, Im rusty as an old barn nail on NEC Article 250 Grounding so heres rusty opinion..... (had I been asked this 15 years ago Id really shine lol)

First of all, services to other remote buildings (what youre doing if I understand your post) isnt quite the same as service to sub panels in the same building. My understanding from Article 250 is that since at the remote location theres more then one branch circuit (I assume thats the case???) A GROUNDING ELECTRODE (driven rod etc) IS REQUIRED

AGAIN thats NOT the same situation where in one building you carry an Equipment Grounding Conductor and a Neutral (Grounded Conductor) to a sub panel in which case THERE IS NO SECOND GROUNDING ELECTRODE at the sub.

If this is all tooooo rusty I hope a currently practicing electrician can bail me out !!!!! !

John T

At the Genset (Im taking it to be a seperately derived source) the Neutral is tied to a grounding electrode such as structural building steel or a made ground such as driven rod as you mentioned (Id keep that on there permanemtly) and is also bonded to the generators metal frame. That "equipment grounding conductor" commencing at the point where the earth grounded Neutral is bonded to the gennys frame, would be carried and bonded to the transfer switches metallic case AND ALSO to the other "equipment grounding conductor" which was carried to the switch from the panel serving as the utility. I DONT ENVISION SWITCHING THAT EQUIPMENT GROUNDING CONDUCTOR but instead have BOTH EGC's tied together and bonded to the switches non current carrying metal enclosure. In that configuration theres ALWAYS an equipment grounding conductor tied back to whichever Neutral supplies the load to carry fault current REGARDLESS if the utility or your genny is the system. True that can take place if you broke n reconnected an EGC, but as I see Article 250 (albeit rusty) the EGC from BOTH sources bonds at the X fer switch and also to its frame.

Thats my best shot, hey I know what I know but also know n freely admit the areas where Im rustyyyyy yy, but my gut just dont like the sound of that breaking or switching any EGC's

John T

AGAIN I dont see any switching of the Equipment Grounding Conductors (EGC) like I take you to mean !!!!! !!!!! I see the Gensets Neutral tied to ground at the genset and also to the sets frame and that EGC (Where N and Frame n Ground all bond) then runs n ties to the Xfer switches frame amd also to the EGC ran from the panel i.e. BOTH EGC's bond togetehr n bond to the Xfer switches metal case PERIOD. That way the Xfer switches non current carrying metal enclosure is bonded to whichever source feeds it, Genset or Utility, so any short to its frame has a return path back to the source to trip the breaker.

I see switching of the Hots n Neutrals in your X fer switch but NOTTTTT TTT the EGC's WHY YOU THINKING AOBUT SWITCHING THEM ????? ????

Also the EGC is still the EGC REGARDLESS if from a main or sub panel, tie them BOTH together at the X fer and tie them to its metal case and switch the Hots n Neutrals from utility or genset and feed your loads with the switches Hot n Neutral outputs and the one common UNSWITCHED EGC

Can someone explain how such is incorrect ORRRR an NEC violation cuz I see it as correct regradless how NEC Article 25o rusty I may be!!!!! !!!!! !!!

Let me know Steve, we BOTH need a good answer or clarification of my thinking here.

Till then "Thats my story n Ima stickin to it" lol Switch Hots n Neutral but bond alllll EGC's and carry the EGC to your loads same as normal.

John T

I dont quite follow your Neutral and green wire talk????? ? To my way of thinkin the EGC's (Grounding conductors) are bare or green and Neutrals (Grounded conductor) white but theres all this NEC proper lingo goin on so Im not gonna open any more worm cans

Best wishes n keep safe n do as your local authority dictates

John T

My house {old} has an outside breaker panel. I take the electricity {temporary} from the meter drop in the panel and run it to a shop. The neutral is grounded in the house panel to a ground rod. Do I need a ground rod at the shop panel or not?? From what I read below, I do not, but mine prolly isn't code.

First of all, services to other remote buildings (what youre doing if I understand your post) isnt quite the same as service to sub panels in the same building. My understanding from Article 250 is that since at the remote location theres more then one branch circuit (I assume thats the case???) A GROUNDING ELECTRODE (driven rod etc) IS REQUIRED

AGAIN thats NOT the same situation where in one building you carry an Equipment Grounding Conductor and a Neutral (Grounded Conductor) to a sub panel in which case THERE IS NO SECOND GROUNDING ELECTRODE at the sub.

If this is all tooooo rusty I hope a currently practicing electrician can bail me out !!!!! !

John T

John T

John T

1) You must provide a separate equipment grounding conductor along with the hot and neutral wires to the sub-panel.

2) You must isolate ground from neutral at the sub-panel. (Or in "Code-ese" the GROUNDING conductor must be separate from the GROUNDED conductor.)

3) It is a code (and safety) violation to attempt to add ground rods to the NEUTRAL in the sub-panel. Don't do it. Among other reasons, any voltage drop in the neutral path back to the main panel will be impressed upon all the exposed metal parts of the sub-panel.

4) The code does not require you to add ground rods to the (separate) equipment GROUND in the sub panel. There is no code provision that I know of that forbids doing it if you really want to, but I don't recommend it (because of the potential for ground loops).

John T

That's valuable information, and your explanation is very clear and informative. This is a subject that falls into a funny category---not only is it a matter that most of us don't know about, but one that most of us think we know about, but don't. Thanks for taking the time to educate us.

All the best, Stan