main grounding conductor

[etechman]

Please help me out to understand the main grounding condutor size i need to install on a 400 amp single phase 240 volt service with no water pipes. This install is on a H-frame in the middle of a grass area for a cell tower. I have parallel 3/0 cu going to a tap box from a utility pole and a 3 gang meter socket plgged into it. I installed a #2 cooper tinned wire from the main tap box to 2 5/8x8' ground rods and the inspector says i have to install 2 3/4 x10' rods and a 1/0 cu wire to both rods. I talk to 2 other inspectors and they told me i'm fine. I would like to get your thoughts on this

thanks

 

[jumper]

2 8 ft 5/8" rods and #6 copper would meet NEC code

 

[etechman]

can you site a article reference #

 

[jumper]

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.

 

[kwired]

Aren't these towers usually engineered with specifications that exceed code minimums on grounding electrodes?

If you have a qualifying CEE 4 AWG copper is minimum NEC requirement, other made electrodes 6 AWG is all NEC requires. If there is qualifying structural steel, on a tower this is a possibility, then 250.66 is used. If CEE or structural steel is used for grounding electrode, supplementary ground rods are not a NEC requirement.

 

[ActionDave]

250.52(5), 250.66(A)

 

[jumper]

Aren't these towers usually engineered with specifications that exceed code minimums on grounding electrodes?

Motorola has a spec book called RG-56, it is a monster.

 

[ActionDave]

Aren't these towers usually engineered with specifications that exceed code minimums on grounding electrodes?

If you have a qualifying CEE 4 AWG copper is minimum NEC requirement, other made electrodes 6 AWG is all NEC requires. If there is qualifying structural steel, on a tower this is a possibility, then 250.66 is used. If CEE or structural steel is used for grounding electrode, supplementary ground rods are not a NEC requirement.

Yes they are, but the meter is not always at the shelter. Very often they are on a pole.

 

[kwired]

Yes they are, but the meter is not always at the shelter. Very often they are on a pole.

OK, if the structure in question is a pole, post, or other separate structure from the tower and there is no electrodes present the most likely made electrode to be installed is a ground rod (or two) and as others have mentioned 6 AWG is all that is required regardless of service or feeder size, a rod will not dissipate any more energy than a 6 AWG can reliably deliver to it.

 

[ActionDave]

Agreed.

Added- Something to consider. There are inspectors that are part of the local AHJ and then there are company inspectors employed by the cell company. These guys come up with some wild stuff

 

[etechman]

I agree with you but the inspector is telling me article 250.28 (2) parallel conductors and that a 5/8 rod cant handle a 1/0 so you have to use a 3/4 x 10' because there is no rating The normal grounding for cell sites are # 2 copper tinned solid wire and all cadwells

 

[etechman]

this is the AHJ inspectors not the cell tower inspector all cell towers use the #2 solid tinned and all cadwell connections

 

[ActionDave]

Somebody is confused. The Main Bonding Jumper and Grounding Electrode Systems are two different things. Their is the reference in 250.28 to Table 250.66, but Article 250.66(A) is clear.

Where did he get the 3/4 ground rod idea?

 

[eprice]

I agree with you but the inspector is telling me article 250.28 (2) parallel conductors and that a 5/8 rod cant handle a 1/0 so you have to use a 3/4 x 10' because there is no rating The normal grounding for cell sites are # 2 copper tinned solid wire and all cadwells

An important step in properly applying the code is understanding the definitions. 250.28(D)(2) is talking about the size of the main bonding jumper. Article 100 has a definition for "Bonding Jumper, Main" an it is clearly not the conductors you are trying to size. Your conductors are "Grounding Electrode Conductors" and 250.28(D)(2) does not apply to them. 250.66 is the section that applies to the sizing of grounding electrode conductors and in your case 250.66(A) as jumper has already mentioned.

Now, if there is engineering on the plans calling for something beyond what the NEC requires, then that is a different story.