Service Ground, Meter Ground and Ground Rods

V

Volt-Amps

Member
Location
Indianapolis
Hello, Forum Experts. I have a few questions I need help with, your help is much appreciated:

Question #1
(2) 100A residential meters next to each other sharing 3/0 feed from utility. The main disconnect is located inside each panel in the respective dwelling unit upstairs. With the service ground being required at the main service disconnect, should the service ground be:
  • One service ground, at the 2-meter enclosure, #4 CU for the 200A service that feeds both panels.
  • Two service grounds, one for each panel, #4 CU, or
  • One #8 for 100A each panel. (I would pick this one, but need experts advice)
Question #2
What rules describe grounding of the meter enclosure. I know it has to be grounded as well.

Question #3
When are ground rods required and how is the number of ground rods determined? Do I need ground rods here?


1709049948777.png
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Grounding from the meter center if POCO allows.
#4 to UFER & water.
#6 (or #4*) to ground rods

(* our POCO requires #4)

The neutral "grounds" the meter base

With a UFER, the NEC does not require a ground rod but your POCO might. Unless you can show 25 ohms or less, drive 2 rods.
With no UFER or qualified building steel, simplest is to drive two rods connected at your meter base.
 
Last edited:
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
See 250.64(D). Basically you can either connect your GEC to the common conductors before they split, or you can run a tap to each service disconnecting enclosure.

The meter enclosure will be factory bonded to neutral so you don't have to do anything with that. It is a convenient place to land the grounding electrode conductor if permitted by your power company (this would be the common location scenario)

Generally you need two ground rods unless there's a concrete encased electrode.

Edit: Augie beat me! He's fast for an old timer!
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
infinity said:
Not that it matters but is the voltage actually 120/208?
Click to expand...
Yeah I noticed that, thought it was strange, but conceivable. Years ago I did almost the exact same service as shown in the diagram, using 230.40 exception #1 for the service disconnects in each unit. I didn't know at time of install, but turns out it was 120/208, POCO called me said I needed to install a 5th jaw in the meters.
 
V

Volt-Amps

Member
Location
Indianapolis
infinity said:
Not that it matters but is the voltage actually 120/208?
Click to expand...
BY looking at the pole, I see 3 transformers. I used a volt meter to measure voltages at each phase and they were all the same, around 210V +/- phase to phase. This system can't be delta, am I correct? If 3 phase Delta, we would have a high leg, I suppose from what I learned in this forum.

1709051868385.png
 
V

Volt-Amps

Member
Location
Indianapolis
So if I grounding is to be at the 2-meter enclosure, there are no service disconnects at the meters. How does that meet code requirement that grounding be at the service disconnect?
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
250.24(A)(1):

(1) General. The grounding electrode conductor connection shall be made at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to, including the terminal or
bus to which the grounded service conductor is connected at the service disconnecting means.
 
V

Volt-Amps

Member
Location
Indianapolis
Volt-Amps said:
So if I grounding is to be at the 2-meter enclosure, there are no service disconnects at the meters. How does that meet code requirement that grounding be at the service disconnect?
Click to expand...
... AND if grounding at the meter enclosure, I need to run the #4 or #6 GEC from the meter enclosure to each panel, correct?
 
V

Volt-Amps

Member
Location
Indianapolis
Thank you so much for helping me understand and sorry if I seem confused, I just want to make sure I understand it once and for all:
- at the panelboard, equipment grounds and neutral are bonded.
- then, from each panelboard down to the meter enclosure, the neutral is run along with the phase conductors, but no ground.
- and at the meter enclosure, is the GEC (#4) which connects to building steel, cold water service entrance and ground rods.
Is this correct?
 
J

jap

Senior Member
Occupation
Electrician
Volt-Amps said:
BY looking at the pole, I see 3 transformers. I used a volt meter to measure voltages at each phase and they were all the same, around 210V +/- phase to phase. This system can't be delta, am I correct? If 3 phase Delta, we would have a high leg, I suppose from what I learned in this forum.

View attachment 2570313
Click to expand...

That dent in the transformer is probably restricting your voltage.
Have the power company pop that out and you may get 214 or maybe even better,,,,,,, :) just kiddin.

JAP>
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Volt-Amps said:
Thank you so much for helping me understand and sorry if I seem confused, I just want to make sure I understand it once and for all:
- at the panelboard, equipment grounds and neutral are bonded.
- then, from each panelboard down to the meter enclosure, the neutral is run along with the phase conductors, but no ground.
- and at the meter enclosure, is the GEC (#4) which connects to building steel, cold water service entrance and ground rods.
Is this correct?
Click to expand...
Sounds correct. One way to think about it is that everything from the service point up to and including the service disconnect is bonded to the neutral conductor. The meter enclosure is factory bonded. If you had say a metal pull box, you would bond it to the neutral conductor also. The bonding jumper in your service disconnect has a special name, main bonding jumper.
 
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