Grounds for 800a service

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Therealcrt

Senior Member
Location
Kansas City
Occupation
Electrician
I’m doing an 800 amp three phase 208/120 V service. I have an 800 amp main disconnect next to my main disconnect is a self-contained 400 amp meter enclosure. The next to that meter enclosure is a 400 amp disconnect that controls a two section 400 amp panel inside my question is about my equipment grounding conductors I need to go from my ground bar in my 800 amp main disconnect over to my 400 amp disconnect, but I passed through the self-contained meter should I put a ground bar in the self contained meter and jump from my 800 amp disconnect to self-contained meter and then from self contained meter over to my 400 amp disconnect or should I just pass through that equipment grounded conductor and put a bonding lock nut or bonding bushing on the inside of my 800 amp disconnect coming from my self contained meter
 
Also i forgot to mention I do not have any concentric or eccentric knockouts they are Al punched and I have rigid nipples between disconnects and meter enclosure
 
That is an odd arrangement. POCO here would not allow the meter on the load side of a service disconnect. If it's a 208 system with no concentrics then you should not need to worry about and bonding bushings/locknuts on the load side of your service disconnect.
I can't see a problem with your EGC landing in the meter and then routing to your panel, however, I may eb overlooking something. Be interesting to see what others say,.
 
Is the neutral in the meter enclosure isolated from the chassis? Many times they are not and cant be isolated, at least on the smaller ones.
 
But the meter can has neutrals from the 800 amp load side which the neutral is bonded in the 800 amp to ground so technically I could just pass those grounds through the meter enclosure and not put a ground bar in the meter enclosure or I could just to be safe
 
Therealcrt said:
Here is the one line diagram
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So if the 800 amp disconnect is the service disconnect then the 400 amp conductors are tap conductors. The EGC for the tap conductors would be sized according to 800 amp OCPD. You need an EGC along with the tap conductors to the meter enclosure and to the 400 amp disconnects. If the raceways are metallic and qualify as an EGC then no wire type EGC is needed.
image-jpg.2580997
 
Therealcrt said:
But the meter can has neutrals from the 800 amp load side which the neutral is bonded in the 800 amp to ground so technically I could just pass those grounds through the meter enclosure and not put a ground bar in the meter enclosure or I could just to be safe
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Potential violation of 250.142(B). Read the details of Exception 2.
 
suemarkp said:
Potential violation of 250.142(B). Read the details of Exception 2.
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Well, considering that this is an engineered drawing city approved this is how it is service conductors three sets of 400 aluminum come into the 800 amp disconnect line side . one set of 500 copper from the load side goes to the existing 400 amp disconnect and then two sets of 250 aluminum go from the load side to the meter enclosure line side from the meter enclosure load side. It goes to the 400 amp disconnect line side from the 400 amp disconnect load side goes inside to the 400 amp two section panel. The meter enclosure has lugs four hots and neutrals since it’s in between my main disconnect and my 400 amp disconnect I decided to put a ground bar inside the meter enclosure since my power company also requires me to run a grounding electrode number six bear copper to every meter enclosure I needed a ground bar anyways so I landed all my grounds two and from both disconnects inside the meter enclosure everything is bonded. The 800 amp disconnect has grounding electrode conductor from the ground rods. Also from building steel and water pipe. The neutral is bonded there at the 800 amp main disconnect like I said this was all engineered already
 
The key item in 250.142(B) Exception 2 is that the meter needs to be immediately adjacent to the service disconnect. These little details don't tend to get put on drawings, but hopefully there is a note to the installer somewhere to do that (or Engineers expect the installer to know the code and mount it accordingly). Using the neutral to ground on the load side of the service disconnect creates a path for objectionable current. Since meters don't tend to isolate the neutral, the code making panel knows this so they require the meter to have a minimal distance from the disconnect.

We could debate all day why objectionable current is bad or not, because you're always going to have it on the line side metering equipment. What difference this current makes on the load side versus the line side I don't know, but they drew the line at the service disconnect for where current becomes "objectionable".

Also, if this was a 1000A service with GFPE, then that GFPE could possibly nuisance trip with neutral grounded meters on the load side. That is the other prohibition in 250.142(B) Exception.
 
infinity said:
No that is a tap according to what's mentioned in the OP. Also if the 400 amp disconnects have 400 amp fuses the 500 kcmil conductors are too small.
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I still don't understand. The drawing says, "4#500KCMIL, 1#3G". What is the 1#3G supposed to mean. I do read and produce One-line Drawings all day long, but there is no consistent style guide that I am aware of.

Thanks,

Mark
 
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