Electrical Grounding

I dug this up from a post I made on another board years ago to help some folks undestand all the electrical ground talk that has been here lately, sorry its longgggggg and may confuse some, but its my best shot and I didnt want to have to do it all over again lol


ELECTRICAL GROUNDING 101


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

First of all, it’s the service NEUTRAL that gets bonded to Mother Earth via a grounding electrode conductor (that bare No 4 copper wire) to made grounding electrodes such as copper rods driven into the earth or metallic water or gas pipes etc. Out at the electrical service 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 (depends on local practice), its again the Neutral that gets tied to Mother Earth. That’s to keep the services and the grid etc. at one 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 notttttttt 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 purpose of the third wire safety equipment green/bare ground is not only so that circuit is tied to Mother Earth and all those ground rods n water pipes, buttttttttt it’s to provide a dedicated low resistance return current path back (for fault current ONLY) 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 so much that bond to earth that can save their life, it’s the drill case or stove being bonded to Neutral back at the panel (via the equipment grounding bare/green conductor) that’s critical. The safety equipment green/bare ground wire is tied to the drills case so if there’s a 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 MAYBE NOTTTTTTTTTTTTTT. 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 butttttttttttttt 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 resistance return current path (like the equipment ground) to trip the breaker.

Sooooooooo it’s the Neutral that gets tied to Mother Earth and driving rods into the earth to “ground” that equipment (saw etc) isn’t the thing, it’s the fact that the equipment grounding conductor (bonded to metal saw case) is bonded to the Neutral at the panel, and as such it provides a return current path back to the panel in case of a short/fault (hot wire to saw case) to trip the breaker n save your life that’s important.

Clear as mud ???? lol John T, toooooooo longggggggg retired Electrical Engineer in Indiana

Is this on a 3 wire system or 4 wire. I though the 4 wire system had the neutral and ground seperate.

yeah, It kinda explains why I can not just run everything with ONE hot wire and just ground the other side back to earth. If it were that simple everybody would do it that way and we would save half our wire expense. On the other hand if I had a metal building I could theoretically hook the neutral side to the building, ground the building both at a stake and back to the box and use the building as a conductor. Not that I have any plans to do such, just thinking out loud.

In North America we have 120 and 240 single phase in homes.

Within that you get 2, 3 and 4 wire wiring methods. 2 wire is almost obsolete.

3 wire 120 and 4 wire 240 always have a ground and neutral both. 4 wire 220 is just so you run 120 v on the same circuit.

An easy way I've explained it to people is, while using a circuit, the neutral voltage floats around depending on a bunch of things. If you cheat and use your ground conductor as the neutral, its voltage will now float, as will the voltage of anything metal grounded on the same circuit.

So you've taken away the escape route for stray current and electrified everything.

Been in lots of barns with this problem. Neighbour broke his arm climbing the hay conveyor. He touched the metal siding and the 40 volts in the conveyor frame went through him to ground. He jerked and fell from 20 ft.

I have the typical farm setup, 3 wires coming from the main disconnect/meter running to various buildings. Each building is considered it's own main, with groundrod. This was proffesionally installed about 2007 or so. Long runs of 200 amp wire 300-400 feet, not cheap wire.

Just put up a new building, and realize, to extend off of this system - will code allow me to continue this 3 wire setup, or do I need to start at the meter with a 4 wire now? Amounts to 500+ feet of wire to go to the meter plus routing it around exsisting stuff. Or just taping off the 3-wire box positioned about 120 feet away & in the clear.

I thought the 3-wire deal was allowed for ag buildings yet, but who knows?

--->Paul

Another common residential grounding code in use here in MN is to use rebar in the footings and or floor in addition to or in place of traditional copper ground rod.

When I ran 220V 100 amp service to my pole barn back in "96 I ran approx 220' of 3 wire 2-0 Aluminum in PVC conduit and believed I was "good to go". I used it this way until" '05 without any problems but by that time I had read many horror stories about not having a dedicated ground on outbuildings.
I then bought enuf #4 copper to run a separate ground back to the main panel and separated the neutral and ground in the barn's sub-panel. Back then, the copper cost me just under $100; I lucked out on that!
There has been enuf discussion on this and other sites to make a believer out of me. I have gained a better understanding of the difference between ground and neutral from postings such as John T's. Thank you!

The typical home system is called 120/240 Volt, Single Phase, THREE wire.......

From the utility to the home you run 3 wires, 2 Hots, 1 Neutral

At the Service Entrance you bond the Neutral to Mother Earth (via the No 4 bare copper grounding electrode conductor to the grounding electrode system such as driven rods and/or pipes and/or footer reinforcement re bar)

To downstream sub panels, you run FOUR WIRES 2 Hots, Neutral, Equipment Ground and you DO NOT RE BOND NEUTRAL TO GROUND AGAIN I.E. THEY REMAIN AS ISOLATED SEPERATE BUSSES IN SUB PANELS unlike the main panelwhere they ARE BONDED TOGETHER often by a big shorting bar that connects the two

John T

Sorry, I cant answer that, its a question for your local utility and if any governing body then must inspect and approve the installation???

3 wire isnt really so bad, it was used for yearssssssssss and whats there may well be grandathered in,,,,,The new NEC (4 wires to outbuildings) is partly concerned with you may have communication lines like phone or internet cables etc etc and depending on if they were grounded properly.

If theres already 3 three wire feeds out of one location I dont see problems with one more but again I CANT ANSWER THAT. Its more important when a main panel feeds sub panels in SAME building that you do NOT re bond Neutral and Equipment Ground but they cut you more slack when its a seperate outbuilding........

If Neutrals get in paralell with Grounds and get rebonded downstream and if the exact WRONG SET OF ERRORS HAPPEN you may be either energizing the Equipment ground (and it ties to your toaster or metal saw or drillcase, I dont like the sound of that, a hot case) and/or using the ground as normal current return although its supposed to be a dedicated path for fault current ONLY.

John T

Youre welcome.

Equipment ground is a dedicated low resistance path for FAULT CURRENT ONLYYYYYYYY so the breaker trips before you dieeeeeeeeeee

Neutral is the normal current carrying return path, its a grounded conductor becasue its indded grounded to eaerth at the service entrance

If N and G are mixed n matched and re bonded downstream in a sub panel and the wrong accidents take place, the ground is carrying current instead of or in paralell with Neutral and/or if things really go bad you may energize an appliances metal case THATS BADDDDDDDDD

John T

Yup, I agree with you.

My setup is legal & inspected & good to go.

Just got to thinking about adding wiring to the new building, I assume I can tie on like planned, but - another hickup to check into. I'll be having a pro do the work, just asking because it's cold & the snow is deep, gives me something to do.

--->Paul

My farm is a 4 wire system.

That would be three phase to be a true four wire system.
A 120/240 single phase is a three wire system.
There are some odd,weird and strange grounded delta and even two different kinds of five wire systems

Paul had a good example a couple of days ago.
Your water may be supplied from one well pump and your hot and cold taps are connected back to that same pump. Your hot and cold taps are still two different devices.

(quoted from post at 22:37:45 02/19/10) That would be three phase to be a true four wire system.
A 120/240 single phase is a three wire system.
There are some odd,weird and strange grounded delta and even two different kinds of five wire systems

Click to expand...

'..three phase to be a true four wire system."

"true"......WTF?

L1, L2, Neutral, safety ground adds up to what? 3?


:roll:
Just stirring the pot, are you?

The ground is always understood. Same as saying 12/3 wire which means two live wires, neutral and a ground wire. 12/3 means four wires.
I've seen a electrical system that used four live lines 90 degree's apart. Even what would be called a 5 phase system instead of three phase.
Some really odd stuff around from the turn of the century beofre electricty was standardized.
Have to say while Nicolas Telsa was challenged socially while dealing with people. He was absolutely brilliant with electricity.

In MN...My brother-in-law had a wire break underground to his house in a farm yard. Years ago you could run wires from your meter pole that had a 200 amp meter setup with side arm handle for REA ON..OFF..Generator ON. This box had taps on the bottom for running wires to your buildings. You could connect anysize wire you needed for your service in each building. 200 amp down to 30 amp. For 240 volt run 2 hot wires and 1 neutral wire and drive a ground rod with a copper #6. THere are lots of Right ways to ground your service..it depends if new or old construction..if metal water lines, etc. You would land the earth wire(ground) and neutral on the same spot at the pole and each main service. This was allowed for years.....BUT....NOT NOW..Last winter when that wire went bad you could repair that wire between between the yardpole and the house..But if you replaced with new you had to bury 2 hots, 1 neutral and 1 ground with a disconnect on the pole for the house. Your neutral and ground would be on the same bar on the yardpole (Meter Main Disconnect). This could be a setup next to your transformer on the ground. In the house you need to separate the grounds and neutrals. Also will have problems with electric dryer and range. Years ago you could run 3 wires now they need to be 4 wire. Now any new farm yards or yards with more that 1 outbuildings need to have a way of shutting off each set of wires going to other building. Now it costs lots of money to do it right....This is what the NEC (National Electric Code) tells us now. Every 3 years we get a new bible. They have a group which gets ideas and from people. They then decide on how to use them. Remember the NEC is the minimum way to wire and there are exceptions to some things. Also ask your local electrical inspector. House wireing now you need GFCI and Arc-fault and tamper-proof recs.Just because your shop was wired a way 15 years does not mean that way is correct today. mnjoe