GES

electricalist

Senior Member
Location
dallas tx
With multiple disconnects ( service) can the grounding electrode IE cold water ,ground rod ,bldg Steel be Daisy chained from 1 disconnect to the next then to the electrode?

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mwm1752

Senior Member
Location
Aspen, Colo
250.64 ( C ) (2) could be interpreted as such -- or run to a buss bar with the continuous EC & then individually to each disconnect is the most common ( the max 6 switch service is grouped)
 

kwired

Electron manager
Location
NE Nebraska
I usually run GEC to one of the service disconnects (the one that requires the largest GEC if there are those kind of diffferences).

I then run tap conductors from each other service disconnect to the GEC.

If you have multiple electrodes you must have unspliced GEC to one of the electrodes, but the others can be connected via bonding jumpers.
 

kwired

Electron manager
Location
NE Nebraska
So if I have 2-xx app disconnects would the GEC be sized by them combined or only by one .

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A common GEC would need to be based on total circular mils of service entrance conductors. I don't know what to tell you for certain if some have copper and some have aluminum SE conductors though.

Individual GEC to each disconnect only needs sized to what supplies each disconnect.
 

infinity

Moderator
Staff member
Location
New Jersey
Just an footnote to that graphic the taps to each service disconnect can be connected via a split bolt or some other mechanical connector, since you are not splicing the GEC an irreversible connection is not required.
 

david

Senior Member
Location
Pennsylvania
I usually run GEC to one of the service disconnects (the one that requires the largest GEC if there are those kind of diffferences).I then run tap conductors from each other service disconnect to the GEC.If you have multiple electrodes you must have unspliced GEC to one of the electrodes, but the others can be connected via bonding jumpers.
• I usually run GEC to one of the service disconnects (the one that requires the largest GEC if there are those kind of diffferences).

250.64 ( C ) (2) could be interpreted as such -- or run to a buss bar with the continuous EC & then individually to each disconnect is the most common ( the max 6 switch service is grouped)
• 250.64 ( C ) (2) could be interpreted as such

With multiple disconnects ( service) can the grounding electrode IE cold water ,ground rod ,bldg Steel be Daisy chained from 1 disconnect to the next then to the electrode?
No.

and why would you want to involve all the unaffected equipment in the chain as the current path to the grounding electrode (s)
250.64 Grounding Electrode Conductor Installation.
• shall be installed as specified in 250.64(A) through (F).
(D) Service with Multiple Disconnecting Means Enclosures. Where a service consists of more than a single enclosure as permitted in 230.71(A), grounding electrode connections
• shall be made in accordance with (D)(1), (D)(2), or (D)(3).

Keep 250.24 in mind as well:
250.24 Grounding Service-Supplied Alternating-Current Systems.
(4) Main Bonding Jumper as Wire or Busbar. Where the main bonding jumper specified in 250.28 is a wire or busbar and is installed from the grounded conductor terminal bar or bus to the equipment grounding terminal bar or bus in the service equipment, the grounding electrode conductor shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected.

• Where the main bonding jumper specified in 250.28 is a wire
• Where the main bonding jumper specified in 250.28 is a busbar


Before you land your grounding electrode to the service equipment metal enclosure with a lug.
Or land your grounding electrode to the equipment ground buss that uses the metal enclosure as a current path to the service grounded conductor.

The green screw you commonly see bonding the Neutral to the metal enclosure and the metal enclosure as the current path to the equipment ground buss is not the allowed path for the grounding electrode conductors current back to the grounded conductor.
 

david

Senior Member
Location
Pennsylvania
A common GEC would need to be based on total circular mils of service entrance conductors. I don't know what to tell you for certain if some have copper and some have aluminum SE conductors though.

Individual GEC to each disconnect only needs sized to what supplies each disconnect.
I don't know what to tell you for certain if some have copper and some have aluminum
I would use 250.28 as guidance

(1) General. Main bonding jumpers and system bonding jumpers shall not be smaller than the sizes shown in Table 250.66. Where the supply conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the bonding jumper shall have an area that is not less than 121/2 percent of the area of the largest phase conductor except that, where the phase conductors and the bonding jumper are of different materials (copper or aluminum), the minimum size of the bonding jumper shall be based on the assumed use of phase conductors of the same material as the bonding jumper and with an ampacity equivalent to that of the installed phase conductors.

(2) Main Bonding Jumper for Service with More Than One Enclosure. Where a service consists of more than a single enclosure as permitted in 230.71(A), the main bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded service conductor serving that enclosure.
 

david

Senior Member
Location
Pennsylvania
To expand on what Kwired posted here's a graphic from the NECH:

Just to clarify
I would make note in the illustration the 350 awg service conductors enter the building.

The common grounding electrode is based on the largest service entrance supplying the grouped enclosures.

• The common grounding electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded service-entrance conductor(s).
• Where the service-entrance conductors connect directly to a service drop or service lateral, the common grounding electrode conductor shall be sized in accordance with Table 250.66, Note 1.
• Note 1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, 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.
 

kwired

Electron manager
Location
NE Nebraska

Just to clarify
I would make note in the illustration the 350 awg service conductors enter the building.

The common grounding electrode is based on the largest service entrance supplying the grouped enclosures.

• The common grounding electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded service-entrance conductor(s).
• Where the service-entrance conductors connect directly to a service drop or service lateral, the common grounding electrode conductor shall be sized in accordance with Table 250.66, Note 1.
• Note 1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, 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.
If the image had two separate entrances of 3 AWG and 3/0 AWG instead of the common 350 kcmil, you would need to add the area of each together and then use that total as basis for sizing the GEC. It only comes up to 220420 circular mils, just so happens to work out that total still requires a 2AWG Cu GEC.
 

kwired

Electron manager
Location
NE Nebraska
How would you like this for a test question on the NEC

A 400 Kcm

B. 600 Kcm

C. 1000 Kcm

D. None of the above
In general I don't like it. If I know how the writer wants to view how the service conductor size is determined... not as much of a problem when it comes to giving the answer they want. I may not agree that it is what the NEC intends though.

How's that for a non specific answer. Needs to be an E. any of the above.;)
 

david

Senior Member
Location
Pennsylvania
How would you like this for a test question on the NEC

A 400 Kcm

B. 600 Kcm

C. 1000 Kcm

D. 800 Kcm
In general I don't like it. If I know how the writer wants to view how the service conductor size is determined... not as much of a problem when it comes to giving the answer they want. I may not agree that it is what the NEC intends though.

How's that for a non specific answer. Needs to be an E. any of the above.;)
How about change the D to 800 Kcm now they have to pick one
 

david

Senior Member
Location
Pennsylvania
To the OP

The common grounding electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded service-entrance conductor (s)

• of the largest ungrounded service-entrance conductor

We have sets of service disconnects (more than one enclosure) implying you have at least one set of service entrance conductors supplying each enclosure.

You can have more than one set of service entrance conductors supplying a single enclosure. In the example I gave disconnect one is feed with two sets of 200 Kcm conductor and defined as a single conductor base on the sum of the circular mil area 400 Kcm. Conductor.

If one of the single service disconnects s supplied by a 500 Kcm (two sets of 250Kcm) than the 400 Kcm (defined single conductor) is not the largest the 500 kcm would be the bases for the rule.

Edit If in your reading of the sentence you remove the word largest than you have a sum of circular mil area of the service entrance conductors

The common grounding electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the ungrounded service-entrance conductor (s)
 
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