Why ground [earth]

[crossman]

In a Sine wave only the positive side of a graph is doing work,

On this note, what I have been taught is that both the positive and negative portions of the sine wave will do work. Here's the reason why:

Take a mostly resistive circuit. Whenever the voltage is positive, the current will also be positive. If we multiply the current by the voltage, we get a positive number, and this extended through time yields positive work accomplished. Now, on the negative half-cycle of voltage, the current flow is also negative. Multiplying this voltage times this current also yields a positive number for power, which when extended through times yields positive work.

Both portions of the sine wave graph will produce positive power, hence positive work. Essentially, it doens't matter which direction the electrons are flowing, they will do an equivalent amount of work in the typical electrical circuit. By typical, I am mean it doesn't contain directional components such as a diode.

Same thing holds true with realistic reactive circuits, except there will be times on the sine wave where we multiply a positive voltage times a negative current, and vice versa. This is because the voltage and current are out of phase. This will still yield an overall positive power, albeit less than simply multiplying RMS voltage by RMS current. This is where the notion of power factor comes from.

In a theoretically perfect reactive circuit, it is possible to have zero work done, because the energy going to the reactor is exactly returned to the source.

I didn't follow some other parts of your post. I couldn't seperate the "code requires it" from "theory says". The fault may lie on my end because I am not an engineer or physicist.

 

[crossman]

Note to TryingHard: I will also agree that your points in post 12 hit the mark, with George's thought from post 13.

 

[dereckbc]

I think it'd be great if the utility did the grounding, and ran an EGC from their xfmr to the service. Then we'd have a lot less problems with stray current. I can see the need for the secondarys to be "earthed" to help voltage stability, but it doesn't do much for the consumer, just the utilities.

That is never going to happen, niether the utility or insurance companies would ever allow it to happen. Think about it for a minute.

You would be betting your life by being protected by the utility. Ever seen and nuetral or phase open in a service feeder? What would prevent the EGC from opening?

 

[iwire]

If, and only if I carried a camera to every site, I could feed you your words. "Properly installed", does not mean "properly maintained". The NEC in my stupid opinion really lacks allowing raceway to be acceptable as an EGC. Quite frankly, I think it's bull.
Again, just my stupid opinion.

Well luckily the NEC applies more then a 'gut feeling' before making un-necessary rules.

Let me ask you this.

The people that improperly install pipe.....are they suddenly going to become better electricians when it comes time to make up EGC terminations?

In other words the installer either cares....or they don't.

 

[Dennis Alwon]

We can go down this road again but this thread has already been there pertaining to the necessity of an egc in metal conduit.

 

[cosmos]

Back to the original question - Besides the NEC and our guesses, is there scientific evidence or studies justifying an "earth" connection for interior wiring ?

 

[suemarkp]

The reason I've heard (still not scientific proof) is that a nearby lightning strike can induce voltage in house wiring (like an antenna coil, and the longer the wire the higher the voltage). This is common mode induced voltage, meaning each wire in a cable becomes X volts above earth. Connecting the bare/green grounding wire to earth will help drag the voltage down to 0 on that wire. The other insulated wires though, could have their insulation damaged by a high induced voltage that isnt' dissipated quickly.

For this voltage on the ungrounded conductors to get dissipated requires (I believe) a surge suppressor (TVSS or lightning arrestor) or some sort. If the wire is rated for 600V, then the arrester needs to clamp below this. I think most meters have a lightning arrester, but TVSS installation is optional. I don't know what voltage lightning arrestors in the meter clamp at. For either if these to work, they must be earthed since the voltage induced in the wiring is relative to the earth. Bonding the neutral to earth fixes that wire, but if it wasn't earthed it too would need a TVSS between it and the wire that is earthed.

 

[RayS]

That is never going to happen, niether the utility or insurance companies would ever allow it to happen. Think about it for a minute.

You would be betting your life by being protected by the utility. Ever seen and nuetral or phase open in a service feeder? What would prevent the EGC from opening?

huh? maybe I'm missing something, but it seems to me that the only issue if the now poco supplied EGC opened would be when working across 2 different services, or between the service and the utility pole. Bonding and EGC's still installed at premises and able to clear faults downstream of the service equip. even with a loss of poco EGC.

I say the ground rod mainly helps the utility, as they benefit from a massive distributed ground system. It does little for the consumer, and the possible benefit (limited due to the generally high resistance) for local lightning protection is often outweighed by the adverse effect of poco unbalance currents flowing thru the premises.

 

[don_resqcapt19]

Ray,

huh? maybe I'm missing something, but it seems to me that the only issue if the now poco supplied EGC opened would be when working across 2 different services, or between the service and the utility pole. Bonding and EGC's still installed at premises and able to clear faults downstream of the service equip. even with a loss of poco EGC.

If the utility installed an EGC from their transformer to the service equipment, there would be no bond between the grounded conductor and the grounding conductor at the building. An open utility EGC would prevent the clearing of any ground faults at or in the building.
Don

 

[ronaldrc]

I have been taught although unusual that with a ungrounded system the voltage can exceed 240 volts.And this is not lightning.I personnelly have never experienced this first hand so do not ask for details of how.



lets assume most on here are right and the earth ground is not worth anything.

There is one thing everyone is leaving out. 120 volts although very lethal,
240 volts is a whole lot more lethal. With the neutral grounded to the earth
120 volts is the greatest voltage you will get shocked with to ground if everything is in accordance with the NEC. If you have a ungrounded system on a 240/120 or a 208/120 volt system if either ungrounded lines happen to become in contact with the ground then you have a shocking hazard of 240 to ground instead of the 120 volts you have with a grounded system. That is a life saver, that alone if nothing else is worth the earth ground.

 

[RayS]

Ray,

If the utility installed an EGC from their transformer to the service equipment, there would be no bond between the grounded conductor and the grounding conductor at the building. An open utility EGC would prevent the clearing of any ground faults at or in the building.
Don

Let me clarify- there would still be bonding on the premises wiring, just no grounding electrode system- POCO would provide a seperate, smaller EGC and the regular neutral. Customer service and xfmrs would still be bonded.

The current GEC systems are generally not adequate to trip a breaker under a fault anyway- it's the bonding that provides a fault current path.

 

[jwelectric]

Curious Minds Have To Know

Q: Why ground [earth] :-?
A1: Common reference point?
A2: Because 250-4(A)(1)&(2)

Why else?

So we can have six plus pages of discussion on the matter

 

[don_resqcapt19]

Ray,

Let me clarify- there would still be bonding on the premises wiring, just no grounding electrode system- POCO would provide a seperate, smaller EGC and the regular neutral. Customer service and xfmrs would still be bonded.

If that were the case there would be no reason for the utility to run an EGC. You would have the smaller EGC in parallel with the neutral between the service equipment and the transformer. The parallel paths for neutral current that are there with the current system would still be there if you bonded at both locations.
Don

 

[RayS]

Ray,

If that were the case there would be no reason for the utility to run an EGC. You would have the smaller EGC in parallel with the neutral between the service equipment and the transformer. The parallel paths for neutral current that are there with the current system would still be there if you bonded at both locations.
Don

I understand what you are saying, and agree that it would be redundant. Just there as a safety ground if the neutral gets cooked. And I know, then there may be too much neutral current on it...

I'm just thinking here. It seems if the grounding electrodes mainly benefit the utility, they ought to install them, and it would give the customers options for blocking utility unbalance current when it's a problem. (i.e. marinas, livestock, and the ever popular ground current thru the plumber) Dunno if it would be feasible technically or bureaucratically.

 

[don_resqcapt19]

Ray,

It seems if the grounding electrodes mainly benefit the utility, they ought to install them, and it would give the customers options for blocking utility unbalance current when it's a problem. (i.e. marinas, livestock, and the ever popular ground current thru the plumber)

While they do provide a benefit to the utility they also provide some protection to the building in the event of a nearby lighting strike or some type of contact with the primary system. I don't see how it would help with the stray current problem. There would still be utility current flowing in the earth from the MGN system.
Don

 

[tryinghard]

So we can have six plus pages of discussion on the matter

Ya think we'd all have somthin else ta do? :grin:

 

[tryinghard]

...With the neutral grounded to the earth 120 volts is the greatest voltage you will get shocked with to ground if everything is in accordance with the NEC.

With all the equipment bonding in place, as per NEC, the fault path will travel to the source (usually XO of the transformer) as extremely high current and instantaneously open its source circuit.

The neutral conductor does not need earth ground for this function.

If you have a ungrounded system on a 240/120 or a 208/120 volt system if either ungrounded lines happen to become in contact with the ground then you have a shocking hazard of 240 to ground instead of the 120 volts you have with a grounded system...

An ungrounded system is one that intentionally does NOT include the neutral (grounded conductor) from the supply source with the phase conductors. A common system is delta 480v ungrounded and bonding to earth is still required, this system is truly 480v to ground earth. But again the bonding is the route for fault current.

 

[iwire]

An ungrounded system is one that intentionally does NOT include the neutral (grounded conductor) from the supply source with the phase conductors.

That is ceratinly true.

But as Ronald said, once one of the conductors becomes grounded (and that will happen) all the bonded parts will have 'line to line' voltage to ground be it 240 or 480.

But again the bonding is the route for fault current.

I can guarantee Ronald is fully aware of the fault current path.

 

[tryinghard]

That is ceratinly true...

But

...There is one thing everyone is leaving out. 120 volts although very lethal,
240 volts is a whole lot more lethal. With the neutral grounded to the earth 120 volts is the greatest voltage you will get shocked with to ground if everything is in accordance with the NEC...

I may be misunderstanding but this is not true with a 120/240 delta 4W; the high leg will be 208V to the case frame while the XO and grounded conductor are bonded to the case frame.

The earth ground does not determine the voltage to conductive items but XO bond to the case frame does. The conductive items are not ground but they are considered grounded,,, UGH (I'm going to get good at this someday then I'll retaire!)

 

[ronaldrc]

Redraw

Redraw

I posted this in the wrong thread sorry



I have redrawn this scenario with the utility grounding jumper.


http://home.comcast.net/~ronaldrc/wsb/High_voltage_illistration.htm

Chances are of this ever happening are very slim.
But never the less it could happen.

And if you are one of the ones that say well anythings possible,
well theres the posiblity it could be your house.

There are other scenarios that could be just as dangerous.

Stuff does happen