Grounding Electrode Conductor at Common Location

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Grouch1980

Senior Member
Location
New York, NY
I'm having trouble visualizing this section in the 2017 NEC: 250.64(D)(3); it describes connecting the GEC to a common location. My questions are as follows:

1) The GEC is connecting to the line side of the disconnecting means correct? It is NOT connecting to the grounded service conductor / neutral INSIDE the disconnecting means, but rather connecting to the GSC before it enters the disconnecting means?

2) What exactly do they mean by 'common location'? What if you have 2 disconnecting means, each one with a set of service entrance conductors tapping off an End Line box / demarcation point from the utility? where's the common location?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
It is just saying that if the connection is on the supply side of all of the multiple disconnecting means, then you only need one GEC connected in one place, as the GEC is 'common' to all of them.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Regarding your second question, if you actually have two separate services from the utility, with separate service points, then you would need one GEC connection for each service. This is different from one service with multiple disconnecting means.
 

Grouch1980

Senior Member
Location
New York, NY
It is just saying that if the connection is on the supply side of all of the multiple disconnecting means, then you only need one GEC connected in one place, as the GEC is 'common' to all of them.
So this means the GEC is connecting to the neutral conductor of the service entrance conductors? before the SEC's split off into the multiple disconnecting means?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Thanks. What's another way to comply with (D)(3)?
We use a ground bus mounted to the wall and run a separate single GEC to each service ahead of the service disconnects from the bus. From there we also hit the CEE and the water main.
 
Last edited:

Grouch1980

Senior Member
Location
New York, NY
We use a ground bus mounted to the wall and run a separate single GEC to each service ahead of the service disconnects from the bus. From there we also hit the CEE and the water main.
Isn't this the same as section (D)(1)? or is it different in where you're landing the GEC at each service disconnect? (D)(1) mentions landing each GEC 'inside' each service disconnect, at the grounded conductor / neutral. You're saying 'ahead' of each service disconnect.
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
250.64(D) gives three options (D)(1), (D)(2), or (D)(3) for when there are multiple service disconnects. (D)(3) allows for a Common Location which would be the single upstream connection of the GEC to the neutral.

250.24(A)(1) allows the GEC to connect at any point upstream of the service disconnect. So if there are multiple service disconnects you can use a single GEC connected upstream of those disconnects to the neutral conductor.

2008 NEC:
250.24(A)(1) General. The grounding electrode conductor connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.
 

Grouch1980

Senior Member
Location
New York, NY
250.64(D) gives three options (D)(1), (D)(2), or (D)(3) for when there are multiple service disconnects. (D)(3) allows for a Common Location which would be the single upstream connection of the GEC to the neutral.

250.24(A)(1) allows the GEC to connect at any point upstream of the service disconnect. So if there are multiple service disconnects you can use a single GEC connected upstream of those disconnects to the neutral conductor.
Ah I see. 250.24(A)(1) clears it up for me... so you can connect at any point upstream of the service disconnect down to the actual terminal inside the disconnect. Letting you comply with either (D)(1), (D)(2), or (D)(3)....
 

infinity

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Location
New Jersey
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Journeyman Electrician
Ah I see. 250.24(A)(1) clears it up for me... so you can connect at any point upstream of the service disconnect down to the actual terminal inside the disconnect. Letting you comply with either (D)(1), (D)(2), or (D)(3)....
Yes that's it. If you want to use a single GEC just connect it before the first service disconnect. We use this method when we have a service switchboard and there are "taps" for the fire pumps and fire alarm disconnects in separate enclosures ahead of the first switchboard disconnect. For our big services there is typically a "tap" section built in for the connection of the "taps". The GEC is connected upstream of the first "tap". Here's a drawing of a recent job:

Tap Section 002.jpg
 

Grouch1980

Senior Member
Location
New York, NY
Ah I see. 250.24(A)(1) clears it up for me... so you can connect at any point upstream of the service disconnect down to the actual terminal inside the disconnect. Letting you comply with either (D)(1), (D)(2), or (D)(3)....
@infinity... my apologies... I was thinking about my question, and the way I worded it may not have been too clear in retrospect... does section 250.24(A)(1) allow for the GEC connection under 250.64(D)(1) to be inside the disconnecting means AND, as an alternative, also on its supply side at the service entrance conductors (still under (D)(1))? The way I read it, (D)(1) specifically says the GEC tap conductors shall extend only to the 'inside' of the disconnecting means enclosure. So 250.24(A)(1) only gives you the flexibility of (D)(3) to exist, where allowed to connect on the supply side.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If I'm understanding your question you're asking if you bring the GEC to a point ahead of the service disconnects and can you also tap that GEC and run a tap conductor to each disconnect?
 

Grouch1980

Senior Member
Location
New York, NY
If I'm understanding your question you're asking if you bring the GEC to a point ahead of the service disconnects and can you also tap that GEC and run a tap conductor to each disconnect?
This is what I mean (I added diagrams from one of the handbooks, hopefully this helps)... Pic A complies with 250.64(D)(1). My question is, does Pic B also comply with (D)(1)?... in Pic B, I modified the connections on my phone for the GEC taps to be on the supply side of the 2 disconnects, to the grounded service conductors (I dashed out the tap connections on the inside of the disconnects). Or is Pic B strictly for (D)(3) only?

Pic A:
IMG_6032.jpg

Pic B:
IMG_6033.jpg
 

Grouch1980

Senior Member
Location
New York, NY
How would you size the conductors in pic B?
In Pic B, each GEC tap I would size based based on table 250.66, based on the size of the service entrance conductors serving each disconnect. So on the left, I would size that GEC tap based on the #3 AWG wire. On the right, based on the 3/0 wire.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
In Pic B, each GEC tap I would size based based on table 250.66, based on the size of the service entrance conductors serving each disconnect. So on the left, I would size that GEC tap based on the #3 AWG wire. On the right, based on the 3/0 wire.
The issue I see with that is that you're ahead of the disconnect so you cannot use the disconnect conductor size to size the GEC.
 

Grouch1980

Senior Member
Location
New York, NY
The issue I see with that is that you're ahead of the disconnect so you cannot use the disconnect conductor size to size the GEC.
Ah. So that means Pic B is invalid, and you cannot make those connections? Meaning Pic C, that I attached here, is the correct way when you are ahead of the disconnects? So this fits into section (D)(3) then, with the common connection? Here I would size the GEC based on the 350 MCM service entrance conductors.

Pic C
8CB761E7-5570-4FDD-B362-200DEDD2F205.jpeg
 
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