Objectionable Current

[gwz2]

Re: Objectionable Current

Not factual, BUT, I would think it is that two deferent Codes are invloved.

The NESC Code is what the Poco use to supply power to a premise.

The NEC Code is what the premise owner is obligated to follow.

In particular on the Grounding issue, EACH code wants to be sure THEIR portion is grounded and not dependant on the other code.

The NEC considers that Grounded Conductor ( usually the neutral ) of a premise system should not be re-grounded after the SERVICE Equipment ( 250.24(A)(5).

This is a method to prevent parallel path(s){ a source of objectional current } of a grounded conductor back to the power source ( i.e. the Service Equipment ) of Poco supplied system.

 

[bennie]

Re: Objectionable Current

Gwz2: The utility distribution system is designed to utilize the earth as a parallel conductor.

The last ground point, of a MGN system, is the ground electrode at the premises service, except when separate buildings are involved.

 

[bennie]

Re: Objectionable Current

When supplying numerous electrodes from the ground/neutral bus, of the service, the MGN is multi-point grounded at the premises.

This is a code violation. Common mode voltage is produced, and current flows on all ground electrode condctors, it should only appear on one.

Everyone tells me that bonding can be done from the top, wrong, it must be at the bottom.

 

[bennie]

Re: Objectionable Current

Take a look at StrayVoltage.org for some information about common mode voltage and current.

 

[gwz2]

Re: Objectionable Current

Bennie,

I had hoped that most BB members noted I did not elaborate on the Poco grounding methods.

In 1946, I started working for contractor(s), on Poco property mostly pole work 33KV, 11KV, 6.6KV , 12.5KV, 7.2KV, 4160V, 480V, 240V systems. Throw in some 132Kv, and 220KV tower work and a few small sub-stations and Switch yards connecting to the High Line work.

Did not do any of the Switchyard equipment line-up work though.

Started doing mainly "Narrow-Back" work in the late 50's. Did do some occasional tower work into the 60's.

This is simply a " SWAG " but I believe with the modern mowing methods of the last "Scores" of years and the quality Poco maintenance, that many of the ground rods at poles are no longer attached to the grounding of the grounded conductor.

Had reason to "just check" a series of Poco poles because of the water GEC carrying more current than the Grounded conductor of the Service Drop, only one Poco pole of 8 , ( each of the 8 poles near the transformer pole ) for this dwelling had ground rods, but had the 6AWG solid was cut or broken off the rod, propably by mowers.

I may not have much engineering, but do feel that I do have some savvy of what acutally happens in the field.

 

[bennie]

Re: Objectionable Current

Glenn: You are very well informed. We both started in a similar fashion.
I worked live line maintenance in a 500 KV switchyard, in the 60s. This was in Nevada.

I also repaired bullet hits on the 500 KV feeder to the So Cal grid. Hunters wanted a trophy

There is data that indicates the multi-earth connection of a MGN system is not as important as insuring the continuity and impedance of the MGN.

Many of the pole grounds do become disconnected. It would be a problem in high lightning areas, when an arrestor or varistor is involved.

[ April 20, 2003, 10:23 AM: Message edited by: bennie ]

 

[charlie]

Re: Objectionable Current

Bennie, Glenn is one of the few people on this forum that I know. I want to let you know that you are right about him. Glenn is a very sharp individual who really knows his trade well. Glenn is easy going and fun to be around. I also call him friend.

Glenn lives in the northern part of Indiana so I don't have the pleasure of seeing him except at the Indiana Chapter meetings of the IAEI. I love to argue with him since he is so sharp.

Whenever I think of Glenn, I also think of Walt. Walt passed away a couple of weeks ago and was another really good individual. I hate the fact that I will never see Walt again. I also hate the fact that I will never meet most of the people that I meet here (I'm not sure that made sense).

 

[wocolt]

Re: Objectionable Current

Bennie, and Dereck
Thanks for your replies I checked out that website and copied the infomaton.
One of the reasons I asked was because I have one of those receptacle testors, Sur-test' and on their menu No.4 it is called 'Highest-voltage ground-to-neutral, and goes on to say is caused by other loads on the branch circuit, or harmonics caused by switch-mode power supplies.
Thas said, any two wire circuit loaded to say 80% of its capacity will have a voltage drop on it and the ground-to-neutral voltage will be 1/2 the total drop Right ?
For the sur-test they recommend that "if the common mode voltage is 4 volts or less it is probably a usable receptacle"... If my assumption of V g-n is 1/2 the total drop then that is an 8 volt drop total and is completely unacceptacle.
The question to me is how in Residential is this unacceptacle as far as common mode voltage goes ?

Another site I visited said , to combat, common mode voltage would be to home-run all the neutrals, and use Electronics grade panels and Electronic grade Breakers( bolt-in type instead of the standard snap in type) and to balance all circuits as much as possible, this would be the ideal case.
Unless there is a system that could be set up that when one load comes on line ,say line-B of 10 amps then automatically Line-A is switched on with a 10 amp dummy-load to balance the neutral, this would be great but there seems to be a huge down side to this.

Wm.Colt

 

[gwz2]

Re: Objectionable Current

Charlie,

Thanks for the Kado's.

I also like to see you at the Chapter meetings.

You also add to the code-panel discussions.

Back to the objectional current.

Only in specialized attempts of small portions of a complex ( premises ) will stopping objectional current be accomplised because of the inductive and capacitve coupling of circuits is everywhere electrical power is.

I believe that a SINGLE POINT of grounding the Grounded Conductor to the EARTH ( and all EGC's also originate at that same point ) but the EGC's may be ( and maybe should be ) bonded to items connected to earth through out the premises system, which is usually in the MAIN disconnect for the premises.

The grounded conductor should NOT be re-grounded, except as permitted in 250.24(A)(5).

Let the adequate sized grounded conductor carry all of the return current to the source and let the EGC's do their purpose under FAULT conditions.

Glenn

 

[bennie]

Re: Objectionable Current

The neutral/ground conductor is an extension of the MGN, which contains common mode current from the multi-ground feature.

The equipment ground conductors are electrically extensions of the MGN system. The equipment ground conductors should not be regrounded to earth for the same reason as the neutral/ground.

Common mode current may not be possible to completly eliminate, but it can be decreased by proper design of the current paths.

It appears that the scientists of the past knew something about negative side effects of EMF.

 

[gwz2]

Re: Objectionable Current

Bennie,

just for one example;

The EGC is permitted to be Rigid Metal Conduit ( RMC ). In any premises where RMC is installed, it is very likely to come in contact with the earth or equipment in contact with the earth just by the proximity of switch gear setting on concrete or steel floors.

Except for the isolated ground receptacle and the use of insulated EGC back to the source grounding, I just don't know of any isolation of a system EGC.

The EGC should only carry current during a FAULT condition of the Circuit conductors that the EGC is installed with.

Some Section References;

250.2
250.4
250.6
250.24(C)
250.80
250.90
250.96
250.134(B)

 

[Ed MacLaren]

Re: Objectionable Current

The equipment ground conductors should not be regrounded to earth

How would you propose that the frames and enclosures of motors, switchgear, appliances, boxes, cable sheaths, piping systems, and the hundreds of other non-current-carrying metal parts of equipment that could become energized, be isolated from ground?

Ed

 

[bennie]

Re: Objectionable Current

250.6 (A)&(B) list the procedures.

 

[wocolt]

Re: Objectionable Current

Bennie:
How do you propose to accomplish this, short of re-doing 50 years of work?
Even systems done 50, 60 years ago carried objectional current, ie Old 60 amp services Piped into the dwellings with 1 inch rigid carried neutral current back to Meter socket(parallel path). Talk about a conduit overstuffed those certainly were. Those old cloth conductors I have no idea how they ever got 3 conductors in there.
And what about the old 30 amp 120 volt systems,, those were just short of disastorous. By your own definition of Common voltage, this was it.
I wouldnt trade what we have to-day to the way it was for nothing. Especially when it comes to safty ease of installation.
I cannot imagine drilling 1 1/2 holes by hand.

Wm.Colt

 

[bennie]

Re: Objectionable Current

The provisions of 250.6 (A) have been in the code for over 50 years. The section may as well be deleted if it is not respected.

 

[wocolt]

Re: Objectionable Current

Bennie:
You are right,we do have "objectionable current" on the water line ,to the ground rods and the metal nipple connection (if installed) between the meter base and the main service panel,(all parallel pathes) and so we have been installing services wrong for the last 100 years or so,,.... But what is the solution ?? Install feeders to every residence ? I mean , a 4-counductor ala, sub-panel.?

Wm.Colt