Inspector's Bad Ground Call 1

[unclesyd]

I had to move the power pole for my shop about 10' as my old ground 3/8" EC Copper 16 ft long is going to be covered up. I installed a new ground made from EC Copper 3/4" rod with 1/4" bore x 20' long and hooked every thing up. It was inspected yesterday and when I went out to get the number off the inspection ticket for the power company the ground was noted as not up to code and had not passed inspection no other explanation.
It is a only a 100 Amp Main and the local codes say 3/8" copper or 1/2" copper plated steel ground rod.

What could be the reason for the inspectors call?

 

[jbartos]

Suggestion: If there is just one ground electrode installed, the measured ground impedance will be required. See Reference:
IEEE Std 80-2000 IEEE Guide for Safety in AC Substation Grounding.
Section: 19.1 Measurements of Grounding System Impedance
for methods:
19.1.1. Two-point method
19.1.2. Three-point method
19.1.3. Ratio method
19.1.4. Staged-fault test
19.1.5. Fall-of-potential method

 

[pennsy]

Skiier:
The 25 Ohm value noted in the NEC applies to the maximum resistance for a single made electrode. If a higher resistance is obtained for a single electrode, a second(paralleled) electrode is required. This should NOT be interpreted to mean that 25 ohms is a satisfactory level for a grounding system.
The wording in the NEC comes down to show me 25 ohms to ground or drive two ground rods.
For a Single phase residential/small commercial of 100 amps as listed above I have never heard of anyone checking the resistance to ground. It can be done, they make a real neat clamp-on tester that is accurate and also fairly expensive.
The requirement of two ground rods that are only 5/8 dia. and 8 feet long is not going to achieve any reuslts better than maybe 15 to 20 ohms to ground.
These ground rods were never intended to trip a breaker or blow a fuse, In the NEC it clearly says that the grounding electrode shall NOT be used as the sole equipment grounding conductor but shall be tied to the Neutral bus to tie the system together.
Also that a grounded system conductor shall be run to each service.

WOC

 

[unclesyd]

To all,
I'm in possession of a electric inspection sticker for the electric service to my shop.

To my great surprise the electrial inspector, the writing looks the same as on the denial paper, came this morning while I was in the process of checking my new ground using power from a heavy duty extension cord, with its' GFI out of the circuit, and using 3 different GF1 devices. He witnessed one test on a very sensitive GFI used by an inspection company that I had borrowed. I informed him that everything that I had tested in the shop to the new ground had tripped a GFI. He made no mention of the previous problem with the ground, in fact he didn't open his notebook on site. I didn't ask as about the previous ground problem, though I should have to give everyone who responded an answer as to why the refusal on the first inspection.
All he did was check the tightness of the treminals in the power panel and the panel inside and put a sticker on the box and said I could call the power company. Until I get power I can use my shop using the extension cord and before everyone gets on me it’s is #9 stranded wire with all the appropriate safe guards.

Again thanks to everyone who responded to my inquiry. I might try to find out what was wrong on the first try once I have power.

jbartos,
The only thing different this time was the ground rod was driven flush with ground as you first suggested.

 

[skiier]

Thanks jghrist for the useful link. I liked the fact that the gnd resistance meausurement method is shown on the first page.

 

[RonShap]

I'm glad you received the sticker. As a side note, a typical GFCI does not use the ground to function. It simply measures current on the hot and grounded conductor (grounded not grounding) and if they are different by a handful of milliamps, it assumes that it is a ground fault and opens.

 

[skiier]

Thanks again jghrist for the useful link. I understand the term "gnd electrode resistance" and how it is derived and applied.
The problem now is that I know more than I want to know. From all the information presented I have concluded that a gnd rod or gnding arrangement installation is generally a "gamble". Albeit, an educated gamble. The gamble being that you have a low gnd electrode resistance or not. Who does soil resistivity tests? I haven't as an Electrician. I did as a Corrosion Tech though and I would have remembered seeing an Electrician measuring soil resistivity in the past. So who is ensuring safe gnds and what constitutes a safe gnd? And when these tests are performed is it in a wet or dry season?
What I am thinking is that depending on the soil resistivity and other variations in your area there may be times of the year where you have a very high gnd electrode resistance and little protection against lightning strikes.You may as well pull all the gnd conductors off the gnding electrode during that time of year. It is also important to note that the resistance in copper gnd bond conductors - that protect you against shock from equipment not lightning strikes - does not change with the seasons. The main and most obvious reason for gnding a system to earth is to offer a path for lightning strikes. Obviously personel safety is improved over a ungnded system but I won't get to the details.
How often does your GND electrode clear a lightning strike. Maybe never. How often does a good bnd in a properly gnded system protect a person from shock. Almost always. So the fact that you have all your gnd bonding conductors to a gnd electrode (one point) is good. Whether the gnd electrode has low resistance to earth is another question and is of very little consequence 99% of the time. The conclusion I have come to is that a properly gnded system requires a GND electrode and proper gnd bonding of equipment.However, gnd bonding is more important for personel safety.

GND ELECTRODE - needed, important
GND BONDING - Absolutely essential, more important than gnd electrode.

So the next time you see someone driving a gnd rod next to a machine in a factory somewhere tell them they are wasting their time. Save someone's life. Who knows maybe they will be the first electrocuted but probably some poor smuck operating the equipment will.

 

[jbartos]

Comment: I am glad that the sticker has been received, and that there is a good grounding and associated electrical safety for the shop