The N.E.C. and groundfault current.

[marc w schecter]

I work for a state university.We have set up a groundfault program.We have installed amp meters on our main distrubition panels on our main bounding jumper to monator and repair groundfault current.WE have been able to get our building to "zero".WE have to check our meters every 3 months.
I have not been able to convince anyone that the N.E.C. says that there should not be any current on the ground except what is explained under art-250-6-c.Our electricial inspectors and engineer's says 5 or 10 amps are ok,but they wont tell me at what amprage level.I have thought the N.E.C.code means zero Can anyone help me clear this topic up.

Marc W Schecter

 

[ron]

I'm not sure that I've ever seen a facility with 0A on the bond or GEC on a regular basis.
A particular value is not stated in the code. IMHO

 

[BarryO]

I believe the NEC requirement is that the current cannot be "objectionable". I also think "objectionable" is not defined.

The actual current is going to be dependent on the ratio of the resistances of the intended and unintended return paths; hard to control.

 

[don_resqcapt19]

Marc,
In many cases there will be current on the main bonding jumper and there is no way around that in some code compliant intallations. In areas where there is a common metal underground water pipe system, it is not uncommon to find 10 to 20% of the grounded conductor current flowing on the main bonding jumper.
Don

 

[marc w schecter]

Ground Fault Current

Ground Fault Current

We Have Found That Our Ground Fault Current Has Come From Poor Workmanship And Parallel Grounding Paths.we Have To Continually Work At Keeping Our Groundfaults Down.when We Finish Making Repairs We Have A Zero Building.
The N.e.c.does Not Define Objectional Current, But It Does Define Non Objectionable Current In 250-6-c.does This Mean That Anything Not Listed Under 250-6 Is Objectionable? This Seems To Be A Gray Area That No One Wants To Define.i Am Trying To Fine A Firm Position From The Code Board.can Anyone Help In This Area?

Thank You,

Marc.

 

[ryan_618]

i Am Trying To Fine A Firm Position From The Code Board.can Anyone Help In This Area?

Make proposal in the 2001 NEC to define objectionable current as "zero". You will then get a reply from panel 5. My bet is that they don't inted "zero" as the requirement, but either way you will have an answer.

Also , you might try making a comment in the 2008 cycle, since there are changes proposed to 250.6. They might, however, consider it new business, and therefore you would have to wait for the 2011 cycle.

 

[marc w schecter]

groundfault current

groundfault current

Thank you for all your replys.We have never had a problem getting our buildings to zero, but it is time consumming. We have always found the cause.
This problem came to our attention when we had to replace all our mech systems in one of our high rise dorms.
We then tracted down all the ground faults and installed a 100 amp meter on the front of the main panel board , and installed a 100/5 C.T. around the main bonding jumper.

Marc.

 

[don_resqcapt19]

Marc,

we Have To Continually Work At Keeping Our Groundfaults Down.when We Finish Making Repairs We Have A Zero Building.

That is not possible in a code compliant installation. The code requires parallel paths. If the only grounding electrode system is ground rods, the parallel path will have enough resistance to limit the ground current to a very low level, but there will still be some...that is assuming that we are talking about current on the main bonding jumper. If you are talking about current on the system bonding jumper for an SDS, then you should be able to get it to zero as there are no parallel paths permitted.
Don

 

[marc w schecter]

ground faults

ground faults

Our meters are showing zero.That is not to say we have less than one amp of current present.We see no current present on our 100 amp gauges.We can induce a ground fault in our buildings and watch our meter move accordingly.I understand your position,it is just that it does describe what we have expereranced with our electricial systems.

Marc.