New Single Phase 1000 amp GEC

[iustacould]

Seems I have more questions than answers now days. I’m finding truth in the saying “The older I get the more I find out how little I know”

1000 amp 1 phase parallel UG service from POCO pad transformer to CT meter. Parallel 400 MCM copper from meter to Wire trough. Landed in power buss and split to multiple ATS and a few 200 amp disconnects all outdoor, then fed to interior panels throughout.

My confusion occurs with GEC size in 2017 NEC.

250.66(A) seems to apply seeing as I’m using rods as my electrodes with an IBT. Reading through other posts coupled with the overall size of the service worries me though. Wondering if I should actually apply table 250.66. I have to be over thinking this seeing as the exception is right in front of my face. Just wanted to see what the experts think. Big difference between #6 and 2/0.

All service equipment is outdoor. Single Family Dwelling with several outbuildings.

 

[480sparky]

#6 is the largest you'll ever need to take to ground rods. Even if your service is 1,000,000 amps.

 

[iustacould]

Thank you. Confirmed my suspicion that I was overthinking it. Glad to have all you folks!

 

[ptonsparky]

Rods will only pass so much current. 6s are adequate to the rods.

 

[tom baker]

If this is a new building you are required to have a Ufer or concrete encased electrode. No ground rods needed.
And a 4 AWG copper to the Ufer or CEC per 250.66(B)

 

[tom baker]

Wow thats a big single phase service! No thought to using 120/208?

 

[iustacould]

Wow thats a big single phase service! No thought to using 120/208?

This monster dwelling (18,000 sqft) is located on a lake peninsula of other large dwellings. The transformer is on a pad (think it’s a 178kva 1ph) and at this time only supplies one other dwelling. POCO has passively requested not to change to 3ph. I think in part, for logistics purposes as the pre existing transformer is still able to hold both dwellings.

 

[iustacould]

If this is a new building you are required to have a Ufer or concrete encased electrode. No ground rods needed.
And a 4 AWG copper to the Ufer or CEC per 250.66(B)

I was under the assumption that ufer's are used for unusually dry conditions. Never had an issue using the standard double rod electrode system for single family dwellings. I’m always open to learn so please let me know what reference I can use that requires this for a new dwelling. Our practice has been to use #4 copper GEC for 400 amps or larger but never found a requirement to do so in our construction atmosphere. Just made the AHJ feel more comfortable.

 

[infinity]

I was under the assumption that ufer's are used for unusually dry conditions. Never had an issue using the standard double rod electrode system for single family dwellings. I’m always open to learn so please let me know what reference I can use that requires this for a new dwelling. Our practice has been to use #4 copper GEC for 400 amps or larger but never found a requirement to do so in our construction atmosphere. Just made the AHJ feel more comfortable.

The CEE may be optional if the footing has no rebar, coated rebar, or rebar smaller than 1/2". If it contains 1/2" or larger standard rebar then you must use a CEE which can be either the rebar or 20' of #4 or larger bare copper.

 

[hillbilly1]

Boss’s house is 800 amp single phase with a 800 amp ATS feeding an 800 amp iLine distribution panel. Way overkill because everything he has is LED and high efficiency gas heat and appliances, but the VP designed it not me (I just have to make it work! They forgot to feed the detached garage/apartment. LOL!) I’m running the entire thing off a 60 kw generator, and with everything on, still only 25 kw load.
Put in a 1200 amp single phase service to a rural general store once, owner was too cheap to put in three phase, even though it was at the pole. Poco had to move everybody else over to the other two phases down the road. Load was about 600 amps. All T12 lighting, and a small grocery section.

 

[electrofelon]

The CEE may be optional if the footing has no rebar, coated rebar, or rebar smaller than 1/2". If it contains 1/2" or larger standard rebar then you must use a CEE which can be either the rebar or 20' of #4 or larger bare copper.

Additionally, if the concrete is not in direct contact with the soil, such as due to vabor retarders, then it does not qualify as a CEE. IMO vapor retarders should be used under footings to prevent "rising damp" in the concrete.

BSI-011: Capillarity—Small Sacrifices

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[kwired]

If this is a new building you are required to have a Ufer or concrete encased electrode. No ground rods needed.
And a 4 AWG copper to the Ufer or CEC per 250.66(B)

I was under the assumption that ufer's are used for unusually dry conditions. Never had an issue using the standard double rod electrode system for single family dwellings. I’m always open to learn so please let me know what reference I can use that requires this for a new dwelling. Our practice has been to use #4 copper GEC for 400 amps or larger but never found a requirement to do so in our construction atmosphere. Just made the AHJ feel more comfortable.

It is not required, unless local rules exceed NEC requirements.

250.50 says :All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system.

CEE's are in there, so if there is a footing with qualifying rebar in it then it is "present" and must be used. If there is no qualifying rebar there is nothing in NEC that requires you to put some in there, is still optional if you want to do so.

A CEE will almost always have less resistance than two or even 10 or more rods - much more surface contact with the soil than a rod has. If you have a CEE there is no requirement to supplement it with other electrodes (such as rod(s)).

 

[iustacould]

Boss’s house is 800 amp single phase with a 800 amp ATS feeding an 800 amp iLine distribution panel. Way overkill because everything he has is LED and high efficiency gas heat and appliances, but the VP designed it not me (I just have to make it work! They forgot to feed the detached garage/apartment. LOL!) I’m running the entire thing off a 60 kw generator, and with everything on, still only 25 kw load.
Put in a 1200 amp single phase service to a rural general store once, owner was too cheap to put in three phase, even though it was at the pole. Poco had to move everybody else over to the other two phases down the road. Load was about 600 amps. All T12 lighting, and a small grocery section.

I greatly appreciate information regarding dwellings over 800 amps. It’s hard to find (not that they aren’t out there) these types of residential loads. I’ve installed and calculated hundreds of 400 amp and lower single family dwellings. This is my first over 400 and it just so happens to be the largest dwelling and service that this GC company has installed. Probably won’t be the last but I absolutely don’t want to be the reason customers go another direction for 16k SqFt + homes. I have posted 2 requests for clarification so far. Will most likely request more information as the project progresses. I find it more than beneficial to have a qualified and experienced group of peers who enjoy passing on excellent information and references to back them up. Mr Holt and his staff have created an environment that has led to this seemingly endless amount of knowledge and input. Again thank you all so much for the help you provide.

 

[iustacould]

Hope everyone is doing well and staying healthy! Just wanted to post this drawing to show my intentions for Service Equipment (***Not to scale). Feel free to critique (or boost confidence). This wall going to be located on the dwelling's master bedroom wing. Due to the finished grade at this area and the amount of clearance above the equipment, I can see no issues with minimum distances. Had to re-draw this after meeting with the GC, Sup, Generator Contractor and homeowner today. Checked on size of CEE's for GEC purposes but found that they are all 3/8" per the GC (what I was told, no further info available). Plan is to split the load parallels in the Service Trough on Power buss (I guess this is considered a "Tap") and feed to all the ATS's. Give me what you got so I can plan ahead to make this work safely and efficiently! Thanks again!

 

[hillbilly1]

Assuming all three ATS are service rated. What size ocp from generator? And #? Looks like two generator feeds, one for the 400's? The other for the 200?

 

[iustacould]

Natural gas (single unit) liquid cooled 120kw B&S. Two feeds. 1 500kcmil Cu parallel for 800 amp (two 400 amp slit 200’s) at main house, 2/0 Cu single for “barn” 200 amp ATS. All ATS are service rated and double as disconnects (installed 15 different times on a smaller scale). Not sure about OCPD at generator but the unit is in the same service court less than 10’ away.

 

[hillbilly1]

The service rated ATS will have ocp on the utility side, but not on the generator side. Shooting from the hip, the generator may have a 400 amp breaker, or possibly a 400 and a 200. Don't know about South Carolina, but I think North Carolina wants both the utility and generator disconnects grouped together. If not, you should be able to tap the both 400 amp switches off the same feeder if it is a 400, but you will need a 200 off that feeder for the barn, unless the other breaker in the generator is 200 or less. Probably time to open it up and see before getting too far ahead in planning.

 

[iustacould]

Roger that. I’m waiting on the specs/cut sheets from the Gen Contractor. Going to meet with him again next week to iron out any other details that come up. Conduit plan has to be solid for next Wednesday. Basement floor concrete phase 1 prep starts end of next week. Gotta have that in and the walls core drilled for feeders by the 17th.

 

[spyderx92]

I had the same question but for 800 amp service. so when do you use the table to size the grounding conductor?

 

[packersparky]

I had the same question but for 800 amp service. so when do you use the table to size the grounding conductor?

When 250.66 tells you to. (A) through (C). (A) for rod, pipe and plate electrodes; (B) is for concrete encased electrodes; and (C) is for ground rings. For other electrodes you use table 250.66

250.66 Size of Alternating-Current Grounding Electrode Conductor. The size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded ac system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C).