GEC Functions/Misfunctions

[don_resqcapt19]

Re: GEC Functions/Misfunctions

I think that we will still need a local grounding electrode with the 4 wire service for protection from lightning and accidental contact with higher voltage systems. Also the 4 wire installation does not solve the problems caused by an open service neutral, the only advantage fo the 4 wires is to eliminate parallel paths for neutral current between the building and the utility transformer. Would the advantages of the 4 wire system jsutify the cost increase of installing that system?
Don

 

[macmikeman]

Re: GEC Functions/Misfunctions

The answer to that question probably would be "Ask the plumber what he thinks."

 

[macmikeman]

Re: GEC Functions/Misfunctions

Interesting side track to this post. Check out the Mike Holt newsletter about the old telegraph system in the USA. One overhead conductor on poles an it used the Earth for the return path. Think about the old western's where the message is sent out from D.C. and they get it way out in Kansas. Apparently the current draw was so low it worked ok.

 

[LarryFine]

Re: GEC Functions/Misfunctions

Charlie, I have to disagree with you a bit. I believe that grounding electrodes serve a purpose beside a neutral-current pathway: bonding between the grounded service neutral and the earth.

In other words, to minimize voltage gradients, so touching metallic equipment cabinets and raceways while standing on the earth doesn't provide a pathway for stray voltages through personnel.

Whether at an actual 0.0 volts to the system neutral and/or earth, it's important that equipment and nearby grounded surfaces be at the same potential, as is assured by swimming-pool bonding.


(The following assumes a 240/120v 1ph service):

As for the original question, it is possible that, with an open neutral, the loads on a lightly-loaded phase could indeed see voltages approaching phase-to-phase voltage when paired with a heavily-loaded phase.

Sure, the phase-to-neutral loads on a service are still in parallel with one another, but the loads on phase A would effectively be in series with those on phase B. The neutral current maintains voltage balance.

For example, if we have 120 ohms of load on phase A and 60 ohms on phase B, with an intact neutral, phase A current would be 1 amp, and phase B current would be 2 amps. Neutral current would be 1 amp.

Now, open the neutral, and we have 180 ohms accross 240 volts, meaning A and B current are both 1.33 amps. Phase A loads would now be subject to 160 volts and phase B loads to 80 volts.

Now, lets look at a resistive, but not totally open, neutral. Let's make up a neutral pathway resistance of, say, 30 ohms (through local water and driven grounds), resulting in a sort of Y system.

The neutral attempts to pull the neutral back towards 0 volts, so the voltage imbalance is reduced, but not eliminated. It is too complicated to calculate the voltage and currents now, but Mike helps.

See: http://mikeholt.com/free/neutral3wire.xls

We now see that phase A sees 137.14 volts and flows 1.14 amps, while phase B sees 102.86 volts and flows 1.71 amps. These voltages are almost within acceptable tolerances; 10 ohms would be even better.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

CharlieTuna:
I live in Atlanta, GA.
I do not believe that a low resistance path exists to complete the circuit in question from the residential service GE system (including the neighborhood-wide unilaterally bonded metallic water main service) to the utility pole GE to the transformer.
The earth is a conductor however.
Fortunately for my neighbor the path for the objectionable current flow did exist - whatever the value of the resistance of that path.
Proof interesting is the operation of the loads supplied by the system and no fire, blown TV, stereo, et.
See Mr. Holt's article recently posted on the history and operation of the telegraph system?

GE system: Lowering the resistivity of the earth by what ever means possible, lowering the resistance of the electrode itself and the connections to it, and lowering the contact resistance between the electrode and the soil adjacent to it is crucial for safe and effective operation of the systems supplied both at the utility pole (source) and at the service supplied.

The current return path by means of earth does pose a measurable resistance to circuit current.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

In the case of a severed neutral a grounding electrode system and earth will serve to complete the circuit back to source.
A recent case scenario I observed showed that true.
Now. Here is a question:
What if the Main Service Disconnect circuit breaker was designed with a tap conductor to the main bonding or equipment grounding terminal bar at the service point. The device senses an objectionably high resistance of the system's grounded conductor circuit return path to source and/or complete loss of that path and then it would trip out thereby removing the hazard?>

Is such a device already available?

 

[iwire]

Re: GEC Functions/Misfunctions

Originally posted by grandpapastu:
In the case of a severed neutral a grounding electrode system and earth will serve to complete the circuit back to source.

I guess that depends on what you consider completing the circuit.

Yes current will flow but not nearly enough to provide a steady, correct voltage at the panel with the severed neutral.

For our purposes as electricians in my opinion the earth will not serve to complete the circuit back to source.

 

[George Stolz]

Re: GEC Functions/Misfunctions

Originally posted by grandpapastu:
In the case of a severed neutral a grounding electrode system and earth will serve to complete the circuit back to source.
A recent case scenario I observed showed that true.

Grandpapastu (cool name, by the way) with all due respect, you seem to let physical proximity mess with your head. A 200' metallic connection to the source beats a 50' earth connection to source seven days a week.

Earth makes a pretty terrible conductor for 120V, that's pretty much a given. There are a couple way more plausible explanations for why there wasn't smoke leaking out and catastrophe in the house. The most likely one advanced is the connected water pipe therory.

It's less likely, but possible that the loads were perfectly balanced, the 120V equipment inside could conceivably see no difference.

It is super-duper-kahzaam unlikely the grounding electrodes would let everything operate normally on their own.

Now. Here is a question:
What if the Main Service Disconnect circuit breaker was designed with a tap conductor to the main bonding or equipment grounding terminal bar at the service point. The device senses an objectionably high resistance of the system's grounded conductor circuit return path to source and/or complete loss of that path and then it would trip out thereby removing the hazard?

Is such a device already available?

Stu, I don't believe that's possible. I ask you this: how would you test for an objectionally high resistance on the neutral with a multimeter? (If you say, via the grounding electrodes, I'll cuff you upside the head. )

The best protection I've seen (in my short time) for an open neutral condition, is surge protecting every sensitive item with a plug strip. A 240V Surge Protector on the service is no good, as the line-to-line voltage never changes during an open neutral. Here's a diagram that Ed MacLaren has drawn, it illustrates the situation perfectly:

120V Plug-strip style surge protectors will protect computers, I know, beyond that I assume. That overvoltage leg of the open neutral will cook the plug strip, but it will protect the equipment.

 

[charlie tuna]

Re: GEC Functions/Misfunctions

i am sure we have all come across problems in our service careers concerning a open service neutral and it's effect on the operation of a residential home's electrical system. each home's ground resistance back to the power source is different depending on soil-depth-distance-conductivity-etc.. your neighbor calls and tells you "when i turn my stove burner "on" the kitchen lights go out" or something to this nature. right away, you consider the neutral! this might be a high resistance return path. and then there are others that aren't so obvious, maybe excessive dimming of lights when certain loads are applied. this may be and return ground path with a low resistance where the ground system is pretty much doing the job of the neutral conductor and returning the unbalanced current back to the power source via the ground rod and earth..

i think, or from what i have seen in 45 years, the ground rod does very little to "reduce" damage caused by lightning! maybe some of you guys have seen differently? i have seen, most of the time, where it comes in on the utility network--tv-phone-power and ignores the fact that the ground rod is right there and then goes off and attacks branch circuit devices while leaving a tracking path --- maybe carbon???---to follow it! at best i can understand that the existing installations "may" help to standardize the potential throughout the entire network --- residential rod(s) utility ground rings under each pole, etc..

on a four wire service drop, there would be complete protection upon an "open nuetral"! as a matter of fact, it would be had to determine!! as mike holt say's in class---"if the ground rod was actually important and served a function, would we be allowed to drive a second rod and "assume" we had a 25 or less ohm resistance ground path back to the power source?". no! we would be required to test and continue to drive rods or extend the depth until this 25 ohm rule was met!!! or maybe install a "chemical ground rod" to assure continued low resistance?? they only cost about $4000,00!!! ??

my pet peeve is the ground rods at utility and light poles! again, it isn't the cost involved, it's actually a safety factor! again, the evidence is not there that shows me that this rod ever has served a function during a lightning strike!(?) it only adds an additional conductor for confusion and also continues to provide the installer and/or maintainance personel an idea by being installed that this "is" a return path to the power source. again, i can understand that the ground rod at pole bases "tend" to stablize system voltage in some small way, and that anyone can argue the effects of lightning since everyone agrees "it's unpredictable"!!! we are killing an average of 370 people a year in the united states due to improperly grounded utility metallic surfaces! and as i read the reports, more than half could have been prevented by the removal of this "ground rod" and it's myth that it serves some useful function!!!

 

[grandpapastu]

Re: GEC Functions/Misfunctions

The prototype main service disconnect circuit breaker would measure voltage drop and current on an integrated test circuit designed with a fixed resistance between phase conductor and equipment grounding terminal bar at the service point.
An open or loose neutral would present signature change in the measurable values triggering the circuit breaker trip mechanism.

 

[iwire]

Re: GEC Functions/Misfunctions

Papa, a simple GFP main breaker would do the job also.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

I am just not so sure that a GFCI main breaker would do the job.
I suspect that it might and then I consider that in the absence of a neutral the GFCI only serves a phase-to-phase load and will not trip.
But then....
I will just have to research the operation of the GFCI further.
Ah, yep: a portion of the current would develop across the GE system.
The GFCI would sense a current imbalance and trip out. (According to only one principal of operation)
Correct?

 

[grandpapastu]

Re: GEC Functions/Misfunctions

Thanks iwire:
you are of course 100% correct on this one.
The GFCI main breaker would do the job and would be performing as it was intended to.

Glad you were paying attention.
Glad for all the reply comments.

 

[benwieland]

Re: GEC Functions/Misfunctions

REMEMBER THAT 240 SPH CKTS ARE OUT OF PHASE BY 90 DEGREES MEANING THAT THEY REACH THIER CORRESPONDING ZERO POINT OF NO VOLTAGE AT DIFFERENT INTERVALS AND CAN ASSIST IN CARRYING UNBALANCED CURRENT BACK TO THE SOURCE. SEEMS LIKE A STRETCH BUT MAYBE, I AGREE THAT THE METAL PIPE IS RESPONSIBLE

 

[bphgravity]

Re: GEC Functions/Misfunctions

Originally posted by benwieland:
REMEMBER THAT 240 SPH CKTS ARE OUT OF PHASE BY 90 DEGREES...

Actually, 3? sytems are three alternating currents 120? out of phase, and 2? systems operate 90? out of phase. Each of the individual alternating currents are 1? currents with poles 180 electrical degrees apart.