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Electrical Grounding

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John T

09-17-2007 08:15:47




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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

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suptscottyb

09-18-2007 20:03:33




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
Here is another topic along these lines. Do all states require GFI (ground fault interupter) circut breakers in all wet and/or outside locations as Calif. has for years?



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djfarmer

09-18-2007 06:26:55




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
I just changed my electrical service at my place to add service to my pole barn. Power comes in to a transformer at the pole, drops to the meter, then to the box below the meter on the pole. From there the power runs to three seperate building( house, garage and pole barn ). There is a ground rod at the power pole. Do I need a second ground rod at the pole barn off of the ground buss bar? Thanks.

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John T

09-18-2007 07:03:58




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 Re: Electrical Grounding in reply to djfarmer, 09-18-2007 06:26:55  
DJ, I just answered a similar question from dave below, heres a copy, its my opinion YES you need a ground at those remote locations.

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

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tech4

09-18-2007 05:48:18




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
John you gave the best description that I have seen on the boards. I agree fully with you as grounding seems such a mystery to those that do not work with electricity every day.



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S. Crum

09-17-2007 21:51:41




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
John here's a question along the same lines. If I install a separate sub panel supplied from the main panel thru a transfer switch so I can break the sub panel from the main and power the sub panel with a 10K gen set, the ground to the sub from the main should also be broke, and the ground then be taken from the gen set? I also will have a ground rod to clamp an earth ground to when using the gen set.

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John T

09-18-2007 06:44:38




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 Re: Electrical Grounding in reply to S. Crum, 09-17-2007 21:51:41  
Steve, Im rusty as an old barn nail on Article 250 (NEC Grounding) so dont bet your life on this, that being said heres my rusty/cloudy opinion:

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

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S. Crum

09-18-2007 07:13:42




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 Re: Electrical Grounding in reply to John T, 09-18-2007 06:44:38  
John,
Your not the only one that's foggy on this. I know that I want to be sure that when the transfer is thrown to the gen set that there is positively no way that the gen set power can be fed back into the line for the protection of any lineman working on the line. I will be running about 100 feet of 2-2-2-4 cable in conduit underground to the entrance area and transfer so the welder/generator can sit off the end of the driveway for easy access. My thinking is that the gen set ground would be established at at ground leg of the 240 volt of the gen set and the neutral be bonded to the gen set frame and the frame is bonded to the ground rod.
The transfer switch is an industrial 60 amp 3 phase switch, so I have the 3rd leg of this to switch the ground from the main panel to the gen set ground. I'm not a big fan of sissy homeowner equipment when it comes to power. The neutrals of the main and the gen set would remain tied to both panels and the ground rod at the main and the rod at the gen set location. Does this make sense? I can ask 3 different electritions around here and get 3 completely different answers
Thanks

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John T

09-18-2007 08:59:29




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 Re: Electrical Grounding in reply to S. Crum, 09-18-2007 07:13:42  
Boy, I reallyyyyy opened a can of worms huh.

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

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S. Crum

09-18-2007 14:57:58




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 Re: Electrical Grounding in reply to John T, 09-18-2007 08:59:29  
John,
Lil Jake at work (licensed industrial and residential) electrical guru cleared this up for me tonight with pictures and all. The ground wire (green insulation) must by code be broken with the power legs in the transfer switch due to the line and the gen set possably having different potentials However the mechanical ground or earth ground or bond wire as this is commonly called in this area should all be lugged to the same earth ground rod.
Jake said I could pay a licensed electrition to do this for me, or I can do it myself as it would be done the same way.
Most of the confusion in this are appears to be in the terminology. "neutral" is the service ground (green wire low impedence). And the bond wire or mechanical ground (bare wire high impedence) gets lugged to the earth ground rod. At least around here.

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John T

09-18-2007 18:49:40




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 Re: Electrical Grounding in reply to S. Crum, 09-18-2007 14:57:58  
Thanks Steve, BOTTOM line is you have to do it however your local authority says. Thats not how I remember Article 250 but its been yearsssss s so I may have to dust off my old code book lol What I really need is an updated one cuz mines no longer the latest revision grrrrr rrrr maybe thats my main problem trying to apply it to todays standards????? ???

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

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Dave in Tx

09-17-2007 19:20:22




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
Question 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.



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John T

09-18-2007 06:58:29




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 Re: Electrical Grounding in reply to Dave in Tx, 09-17-2007 19:20:22  
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

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dr. sportster

09-17-2007 13:19:37




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
Since the grounding conductor and the grounded conductor are two separate things and two different color wires it should be understandable.If you are going to do some installation without inspection youll never know mistakes untill an electrucution occors.I always said you can do your own electric and you can do plumbing too but unless you want the walls to look like crap hire a qualified drywall finisher.Otherwise its five coats of spackle and dust everywhere.PS John using the gas pipe was dissalowed in several codebooks past.Probably not a bad idea to not land grounds on gas pipes.

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John T

09-17-2007 13:50:13




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 Re: Electrical Grounding in reply to dr. sportster, 09-17-2007 13:19:37  
Thanks for the code update (NOT bonding to gas pipes), not practicing in an area for years reallyyyyy yyy causes it go get away from a feller.

John T



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Dick L

09-17-2007 10:20:57




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 Talking About Ground Stakes in reply to John T, 09-17-2007 08:15:47  
Just a note from an old mans farm memorys.
A common practice when I was a kid for small chicken coops on runners that were pulled out in a field so young chickens could be in clean green grass was to run one wire on poles to the coop and then drive a stake in the ground to complete the circuit and have lights at night.



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John T

09-17-2007 11:29:41




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 Re: Talking About Ground Stakes in reply to Dick L, 09-17-2007 10:20:57  
When we were kids n wanted fishing worms we stuck a coat hanger in the earth n attached a hot 120 wire n waited till they wiggled n squirmed up outa the ground and also tied hot wires to metal garbage cans on wood blocks to deter cats n dogs wooooo hooooo wonder we werent all electrocuted huh

John T



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Dick L

09-17-2007 10:13:07




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 Very Good in reply to John T, 09-17-2007 08:15:47  
Got all of that way back in code school but I guess I didn't know that people were trying to drive stakes in the ground to connect the safety ground wire between the circuit breaker/fuse and the equipment.



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jjamna

09-17-2007 09:56:06




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
Well said John, Being a Master Card carrier myself. I just have to shake my head at some of the things discussed in these forums. If I could put it in writting like you did, I would, but I can't. So thanks. Maybe some lives will be saved.
Jeff



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Arkandan

09-17-2007 08:48:20




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
Well thank you John! You're a good and thoughtful person. You're making things come into focus. Just one thing; if I drive a ground rod at a sub panel location and tie a #6 copper to it and to the neutral bar (isolated from the ground bar) on the panel am I improving the circuit or degrading it? If it's an improvement I'll do it for safety sake. If it degrades I'll drop it for the economics of it and presumably a safety concern. Thank you kindly.
Dan

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David - OR

09-17-2007 13:11:20




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 Re: Electrical Grounding in reply to Arkandan, 09-17-2007 08:48:20  
If the subpanel is in the same building as the main panel, then:

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).

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John T

09-17-2007 11:27:47




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 Re: Electrical Grounding in reply to Arkandan, 09-17-2007 08:48:20  
Theres no code provision for such Im aware of (notwithstanding sub services to a seperate outbuilding) but its been manyyyyy moons since I retired from the practice. While neutral is mother earth grounded at the pole n meter base or panel etc I dont forsee earth grounding it anywhere after the main distribution panel, might create some sort of ground loop or multiple current paths in paralell with which a person might find themselves n I dont like the sound of that. Sorry I cant really explain that one good as my initial point but Im just gonna go on record as saying I wouldnt do it.

John T

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Bus Driver

09-17-2007 09:55:50




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 Re: Electrical Grounding in reply to Arkandan, 09-17-2007 08:48:20  
Grounding the NEUTRAL at ANY point after the main panel creates potential electrical hazards for PEOPLE. No problem as it relates to equipment, but not good for PEOPLE. Do not add any type grounds to the NEUTRAL.



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Stan in Oly, WA

09-17-2007 08:47:38




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 Re: Electrical Grounding in reply to John T, 09-17-2007 08:15:47  
Hi John,

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



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