GEC to Neutral

[W@ttson]

Hello,

The GEC can terminate on the incoming service line neutral, in the meter can neutral, or at the main service disconnect neutral.

The MBJ must be at the incoming service neutral to bond the neutral to the case/ EGC bar.

The GEC CAN land on the grounding bar terminal bar if there is a wire type or buss bar type MBJ connecting to the neutral bar where the service neutral lands.

Question: Why is it so important the GEC land on the neutral bar? The GEC and the ground electrodes are really only used for reducing insulation stress from built up voltage/charge from over voltages, lightning, load switching etc. The MBJ is the main tool that does the clearing of faults. If all equipment is properly bonded, and there is a line to case fault, the fault current travels through the mental enclosure to the EGC, back to the service disconnect, hitchhikes a ride on the MBJ to the neutral and sent back to the source to clear the fault. The GEC and the ground electrodes play no role in this, so why is it important for the GEC to land on the neutral?

Is it because there is where it is doing its charge reduction magic - at the neutral?

 

[ptonsparky]

Possibility of poor or intermittent connection to the neutral. I've seen and corrected them.

 

[W@ttson]

Possibility of poor or intermittent connection to the neutral. I've seen and corrected them.

loose or intermittent connection to the neutral which in turn would not allow it to discharge the built up charge?

 

[LarryFine]

Question: Why is it so important the GEC land on the neutral bar?

Answer: Because, especially in the early days where everyone had metallic water piping, the goal was to re-establish the neutral as the zero-voltage reference.

Even nowadays, we often see evidence that electrodes carry appreciable neutral current, especially when there is a defect in the service neutral pathway.

 

[wwhitney]

A related question is why is the GEC required to be unspliced?

If you accept that the job of the GEC is to connect the neutral to the earth, then and that the GEC is supposed to be unspliced, then it follows that the GEC should connect directly to the neutral, and not connect via the MBJ and possibly a section of EGC.

Cheers, Wayne

 

[W@ttson]

the job of the GEC is to connect the neutral to the earth

Why is that the job?

The NEC talks about the ground electrodes to provide charge dissipation from built up charge. This is true for the main service location and at separate structures.

LarryFine mentions that the reason also is to make the neutral a voltage reference of 0 and that there is evidence that ground electrodes carry some neutral current.

I guess in both of those cases above it is important to be no questions asked direct connection to neutral.

 

[ptonsparky]

Larry's answer, no splices.

 

[W@ttson]

Larry's answer, no splices.

yes, why? Not just code reason (because code says no splices), what is the physics behind it.

I think wwhitney is getting at it with saying the job is to connect neutral to earth, but why. Why is it its job, what is the physics behind it.

The NEC talks about charge dissipation as the purpose of the ground electrode system. It has to be that they want to make sure that this occurs and for this to occur, you must connect the neutral to ground - that is how you dissipate the charge.

 

[LarryFine]

You need to consider the average mindset when electricity was new around 100 years ago.

Many older rules still exist because nobody ever came up with a good reason to change them.

 

[ptonsparky]

You need to consider the average mindset when electricity was new around 100 years ago.

Many older rules still exist because nobody ever came up with a good reason to change them.

FWIW, I remember watching what I thought were balls of lightning roll along the primary power lines East of our rural house. That would have been mid 50s.

 

[jaggedben]

Simply, I think it's because the neutral is the grounded conductor. If nothing else, the way the code is written serves to educate people what a grounded conductor is. It's supposed to be grounded, not incidentally bonded to other stuff that is grounded.

 

[jaggedben]

yes, why? Not just code reason (because code says no splices), what is the physics behind it.

I think wwhitney is getting at it with saying the job is to connect neutral to earth, but why. Why is it its job, what is the physics behind it.

My personally belief is that the main reason is so that if a high voltage line breaks on a pole and falls onto the grounded conductor below it then there will be reduced earth impedance to trip ground fault detectors on the high voltage source before too much damage is done. People will say other things, like it helps dissipate lightning charge. They are all a little bit true.

The NEC talks about charge dissipation as the purpose of the ground electrode system.

It does? Where? I think it only talks about limiting imposed voltage, in 250.4(A)(1)

If the voltage between exposed metal and ground is predictably near zero, that reduces shock hazard. But this only works if the whole system is reliably grounded at multiple points.

 

[W@ttson]

It does? Where? I think it only talks about limiting imposed voltage, in 250.4(A)(1)

Yes, that’s the one:
250.4(A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.
Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.


Mike holt in a video on grounding and bonding dissects this portion and talk about how we evolved from ungrounded systems. The ungrounded systems were prone to insulation stress due to built up charge from all those transients talked about in 250.4.

 

[LarryFine]

Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.

Even though these details aren't spelled out in the NEC, they sound like the rules for lightning earthing.

 

[W@ttson]

Even though these details aren't spelled out in the NEC, they sound like the rules for lightning earthing.

I thought the same thing when reading it.