Undersized Grounding Electrode Conductor

[Engineerintraining12]

Hello everyone,

This is my first time posting to this forum and I had a question that I've been obsessing about for about a week now. I am an engineer in training and relatively new to this field, so I am still learning on a daily basis. The other day I noticed on one of my previous projects that I undersized my grounding electrode conductor and main bonding jumper. The project had an 800 amp main distribution panel with two sets of 500 kcmil for the service entrance. When I went to size the grounding electrode conductor, I accidentally sized it for only one set of 500 kcmil using table 250.66 in the NEC. Instead of using a 2/0 wire I used a 1/0 for my grounding electrode conductor size as well as my main bonding jumper. I know that having an undersized grounding electrode conductor can lead to the possibility that when there's a fault current, the cable could burn up when transferring the fault current to the grounding electrode, but I wanted to know if being off by one size (1/0 instead of 2/0) poses a huge compromise to safety or if the 1/0 would be able to handle most fault current situations. The project is already built and the contractor may have picked up on the mistake, but I needed some peace of mind on this question. This is a mistake that I surely won't be making in the future.

Best Regards

 

[waross]

That question is more interesting than I first thought.
Note; I don't suggest ignoring the code, however the question has to do with the safety of the installation.
I don't have the NEC but:

The 2012 edition of the Canadian Electrical Code sizes the main bonding jumper based on the ampacity of the service conductors. The ampacity of parallel 500 MCM exceeds 800 Amps so 2/0 cable would be required.

The 2015 edition of the Canadian Electrical Code sizes the main bonding jumper based on the size of the service conductors.
If we consider the two 500 MCMs to be the equivalent of one 1000 MCM then a #1 AWG cable would be required.
However;
In the case of parallel feeders, The 2015 edition of the Canadian Electrical Code now requires the grounding conductor to be run in parallel also. If this were to be installed under the 2015 edition of the Canadian Electrical Code you would require a #3 AWG conductor to be run in close proximity to each group of 500 MCM conductors.
You may have slightly higher touch potentials.
Quite possibly the contractor felt that it would be cheaper to just use the proper cable than to argue with you and/or the AHJ.
This may be more of an issue of noncompliance with the current code.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[xnuke]

This is both an ethics and safety question. This is a design error that causes the facility to not meet an electrical safety code. Code is law - that's why it's called a code and not a standard. You need to report your undersized grounding electrode conductor (GEC) to your supervisor and let them take the appropriate action to rectify the problem with the client. They may pursue a variance from the AHJ. You don't get peace of mind until the issue is resolved. Keep your head up and admit your mistake. Everybody makes them. It might hurt for a while, but you learned and won't do it again.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[resqcapt19]

I would be much more concerned about the undersized main bonding jumper....that is the fault clearing path. The grounding electrode conductor plays a very small part in the fault clearing process.
What is being used as the grounding electrode? The NEC would permit a #6 copper grounding electrode conductor if the grounding electrode was a driven rod. The only grounding electrodes that actually require a "full size" (per Table 250.66) is a metal underground water pipe or building steel.

 

[Engineerintraining12]

Hey everyone,

Thank you for the responses, I appreciate the help. I have attached an image of the detail I used. The PE that I work under didn't seem to be super concerned about it. He said that if you have a fault condition that is enough to melt the 1/0 cable then you've got more problems to worry about then the grounding electrode conductor failing. I don't think he was concerned though because the contractor that we work with used the proper size in the field.

Best Regards