grounding electrode conductor

[jbolen]

If you have a building with three round rods ten feet apart.
This is a 400 amp 480/277 service.

1. What is the minium size wire between these rods?

2. What is the min. size conductor used as the grounding electrode conductor?

3. The way I read it #6 is min size wire required to a drived grd rod.

 

[iwire]

As far as the NEC 6 AWG copper is largest you need, job specifications or power company requirements may require larger conductors.

 

[bphgravity]

1. The MINIMUM size cannot be less than provided in Table 250.66 of the NEC.

2. Same as answer to #1.

3. Not eactly. Section 250.66(A) states #6 would be the LARGEST required GEC fo for a rod type electrode. Per Table 250.66, #8 CU GEC's are permitted for services consisting of #2 or smaller ungrounded service-entrance conductors. Obviously, this would not apply to your specific question.

 

[erickench]

The NEC doesn't seem to require a specific size for conductors connecting different ground electrodes together except in the case of communication circuits. For these installations a no. 6 AWG is required.

 

[raider1]

The NEC doesn't seem to require a specific size for conductors connecting different ground electrodes together except in the case of communication circuits.

250.53(C) has the requirements for sizing bonding jumpers connecting grounding electrodes together to form the grounding electrode system. This section requires the bonding jumpers to be sized in accordance with 250.66.

Chris

 

[eprice]

The NEC doesn't seem to require a specific size for conductors connecting different ground electrodes together...

250.53(C) applies to these conductors. It refers us to 250.66 for sizing.

 

[erickench]

Gee Thanks. I've been looking high and low for that one.

 

[raider1]

Gee Thanks. I've been looking high and low for that one.

Your welcome.

Chris

 

[ohmhead]

Well i guess iam getting old please help me to understand this ?

A no. 6 wire ?


This is what ive been doing i go to the 310 .16 table and pick my feeder conductor .

Then i go to table 250.66 and pick the size or grounding electrode conductor .

400 amp service lets just say its over 3/0 paralleled or you may just use one run of 600 mcm .


Just do not see a no. 6 for this service i see a 2/0 copper now what am i doing wrong please explain what did i miss in the code not understanding this .

 

[roger]

Well i guess iam getting old please help me to understand this ?

A no. 6 wire ?


This is what ive been doing i go to the 310 .16 table and pick my feeder conductor .

Then i go to table 250.66 and pick the size or grounding electrode conductor .

400 amp service lets just say its over 3/0 paralleled or you may just use one run of 600 mcm .


Just do not see a no. 6 for this service i see a 2/0 copper now what am i doing wrong please explain what did i miss in the code not understanding this .

When dealing with rods, pipes, or plates you can stop reading at 250.66(A)

250.66

(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or (A)(7), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

Roger

 

[iwire]

400 amp service lets just say its over 3/0 paralleled or you may just use one run of 600 mcm .


Just do not see a no. 6 for this service i see a 2/0 copper now what am i doing wrong please explain what did i miss in the code not understanding this .

For that service you would need at least 2/0 copper to the water pipe.

But you would not need more than 6 AWG to ground rods 250.66(A).

Or no larger than 4 AWG to a concrete encased electrode 250.66(B)

Or no larger then the size of the conductor used to make a ground ring 250.66(C)

 

[ohmhead]

Well iwire ,Roger i guess for years i never looked at these articles as close as this.
Mostly our plans show on the risers a grounding electrode which will match table 250.66 or larger i honestly have never installed a GEC smaller then 3/0 since ive been doing electrical iam surprised to see i never really understood this always used what engineer picked .

I need to look at this in more detail trying to see how they came to design or picked this smaller size no .6 cu wire for grounding to rod or rods and why?
Well just for my own benefit or maybe others in the trade who still think 250.66 is what we use .

Iam going to read further about this its kinda interesting to me to see why ?

 

[Dennis Alwon]

I think it is very clear that T250.66 is for the gec to the water pipes, building steel but not to the ground rod. 250.66(A)make it clear that a #6 is all that is needed to a ground rod

 

[ohmhead]

I think it is very clear that T250.66 is for the gec to the water pipes, building steel but not to the ground rod. 250.66(A)make it clear that a #6 is all that is needed to a ground rod

Well yes i agree it is clear and i see that .

Just looking into why the electrical engineers on any project does not use a no. 6 cu ever for ground rods ?