Grounding Electrode Conductor Question

[GingerZap]

I am in an Electrical Program taking an NEC 1 class and my teacher is no help. I am wanting to check my work to make sure I am on the right track. Below is the question and how I solved it. Can anyone verify if my answer is correct?

A multifamily dwellings service-entrance conductors consist of four paralleled sets of 3/0 AWG THHN copper conductors. What size copper grounding electrode conductor is required?
2/0 AWG

Table 250.66 is used to size grounding electrode conductors for A/C systems. Note 1. States If multiple sets of service-entrance conductors connect directly to a service drop, set of overhead service conductors, set of underground service conductors, or service lateral, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.
My understanding of that is that you would add up the areas of the parallel conductors and use the combined area to size your grounding electrode conductor using Table 250.66. Does that sound right? My work is listed below.

(1) 3/0 AWG THHN Copper conductors' area is 167,800 per Table 8, Chapter 9.

167,000 x 4 parallel conductors = 671,200 cmil = 671.2 kcmil

Table 250.66 states Copper conductors Over 600 kcmil through 1100 kcmil requires a 2/0 AWG Copper Grounding Electrode Conductor.

 

[roger]

The question would need to tell you what electrode(s) are being used.

 

[petersonra]

My answer is #6

 

[suemarkp]

I would say 2/0 unless the type of electrode is stated. Those electrode specific sizes are permitted reductions from the normal size required.

 

[Tulsa Electrician]

The question would need to tell you what electrode(s) are being used.

This is the first step.
The question has multiple answers.

My answer is #6

His ansawer I do believe would be based off of a rod type electrode.

I would say 2/0 unless the type of electrode is stated. Those electrode specific sizes are permitted reductions from the normal size required.

This ansawer would be based off of table 250.66
Review 250.52 Grounding electrodes.
You will see there are multiple ansaweres based on type.
Then go to 250.66 size.
My ansawer would be 250.50
6 cu, rod
4 cu , concrete encased
2 cu, ground ring
2/0 cu, table 250.66

 

[GingerZap]

Thanks Fellas, Good Information

 

[tom baker]

You have the right attitude. A lot of what is passed on to new electricians is wrong. Or the code has changed. We see a lot of electrical myths here, example - the ampacity of #12 THHN is 20 amps. Look up what you are told and certainly ask here.
Thank you for your service.

 

[infinity]

The question should have asked for the maximum size GEC required which fits the answer of #2/0.

 

[GingerZap]

Thank You Tom