Grounding Electrode Conductor???

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tley10

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We have been asked to sit at an appeals meeting because a local electrician appealed a turn down on his grounding electrode conductor size. This is a 400 amp service with two 200 amp panels. The local electrician is trying to use 250.66(A) which states that the GEC only has to be a 6 AWG copper when connected to rods. From what we have read being that you would have multiple disconnecting means you would have to go by 250.64(D)(1) to size the GEC which tells you to use 250.66 chart. Are we correct?........ I have a little problem with 250.66(A) because the way it reads, the GEC shall not be required to be larger than 6 AWG copper when connected to rods, is that for any size service?, what if you had a 2500 amp service, would you still be able to run 6 AWG copper to ground rods?
 
The electrician is correct. You can have a 2000 amp service and a #6 is all that is required to the rod. Now the #6 must be either connected at the service ahead of the discos or it needs to be connected to both panels
 
tley10 said:
What about 250.64(D)(1) building with multiple disconnecting means (1) common grounding electrode?
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Which method was used: (D)(1), (D)(2), or (D)(3)?

250.64(D)(1) says the GEC shall be sized in accordance with 250.66... which includes 250.66(A).

250.64(D)(1) does state the GEC must be installed in accordance with Table 250.66, note 1... for service-entrance conductors that attached directly to [line-side service conductors*]... but it is referring to is where each enclosure its own service entrance conductor, as opposed to being spliced or tapped from a "main" service entrance conductor [set or sets].

*What else are they going to connect to on the line side. :slaphead:
 
They are not connecting to nothing else but those two panels. Land on one and tap to the other. I dont see where in 250.64 (D)(1) that it talks about connections to building steel, water pipes, etc.
 
tley10 said:
... Land on one and tap to the other. ...
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That could be a problem.

The tapping must occur outside the disconnecting means enclosure. First sentence, second paragraph of 250.66(D)(1) states "A grounding electrode conductor tap shall extend to the inside of each disconnecting means enclosure." That implies and one can infer that the tap cannot occur within any of the disconnecting means enclosures.
 
It has somehow been determined that a ground rod can not dissipate any more energy then a 6 AWG copper conductor can deliver to it, therefore no point in requiring a conductor any larger then 6AWG.

Similar for concrete encased electrodes except it is 4AWG.
 
From ground rod to its first termination will always be 6# max -- the design of the electrode system may require the supply side bonding jumper to be different -- what is the supplemental electrode used for this building & does it bond together with the ground rod prior to continuing to the service connection?
 
This is constantly confusing it seems for AHJ's. I probably get this question as much as anyone. Look if it's ground rods...it doesn't matter if it's multiple service disconnects or a single seevice disconnect...if ground rods are used then 6 CU AWG is the largest the GEC has to be ...if their is a common ground electrode scheme setup for multiple service disconnection means (grouped) yet still only ground rods....6 CU AWG is all that is needed.

Comments based on the 2017 National Electrical Code.
 
mwm1752 said:
From ground rod to its first termination will always be 6# max -- the design of the electrode system may require the supply side bonding jumper to be different -- what is the supplemental electrode used for this building & does it bond together with the ground rod prior to continuing to the service connection?
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This is not our job so I dont know the details of it. So if the power comes into the meter base 400 amp fed and feeds two 200 amp panels, and the building is not metal and does not have copper water piping then 6 Awg copper is fine. From what i read if you have to ground anything else then the whole GEC needs to be sized by 250.66
 
tley10 said:
This is not our job so I dont know the details of it. So if the power comes into the meter base 400 amp fed and feeds two 200 amp panels, and the building is not metal and does not have copper water piping then 6 Awg copper is fine. From what i read if you have to ground anything else then the whole GEC needs to be sized by 250.66
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A GEC or bonding jumper that connects to any electrode other than a rod, pipe, plate, or concrete-encased electrode, or a ground ring must be sized per Table 250.66. That leaves:
  • Metal Underground Water Pipe
  • Metal Frame of the Building or Structure
  • Other Listed Electrodes
  • Other Local Metal Underground Systems or Structures
 
tley10 said:
This is not our job so I dont know the details of it. So if the power comes into the meter base 400 amp fed and feeds two 200 amp panels, and the building is not metal and does not have copper water piping then 6 Awg copper is fine. From what i read if you have to ground anything else then the whole GEC needs to be sized by 250.66
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The key is that the rods are the sole electrode that the system grounded conductor (neutral) is bonded to. The sole portion from the grounded conductor to the rod(s) grounding electrode never has to exceed #6 AWG.

If a grounding electrode system is built from the system grounded conductor to electrodes daisy chaining different electrodes than the system has to be built making sure that the conductors do not violate the larger required size grounding electrode conductor linking different electrodes together
 
tley10 said:
This is not our job so I dont know the details of it. So if the power comes into the meter base 400 amp fed and feeds two 200 amp panels, and the building is not metal and does not have copper water piping then 6 Awg copper is fine. From what i read if you have to ground anything else then the whole GEC needs to be sized by 250.66
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electrode in series -- ground rod to next electrode 6# max, next electrode to service 250.66 for electrode conductor size -- different electrode to ground rod to service 250.66 for different electrode conductor size even if it is greater than 6# goes all the way to service --
 
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