I just received an engineers drawing for a 400 amp underground service to a single family house. Here is what I do not agree with and I am sure I will have support on this forum. From pad mount transformer he has 6 300mcm xhhw Al being run in single 4" PVC to meter pedestal along with a 1/0 CU ground. Is the ground wire from padmount to meter pedestal o.k.? From meter pedestal we have two runs of 4/0 AL xhhw in separate 2 1/2" pvc conduits going to house and each run has a #2 Cu ground wire in it. First run hits a main disco. inside house for supply of a 200 amp panel at other end of house (PP2) second run hits 200 amp panel (PP1). Grounding - this is where the problem with design seems to be, is as follows- #2 CU from water line hitting main disconnect and then 200 amp main panel. My question here is no detail is given. Shouldn't #2 CU be continuous through the main disconnect hitting ground bar and then go on to PP1. Also is the #2 CU in both runs from meter pedestal correct? I must admit I am confused with what I have been presented here. Also am I correct to be keeping my grounds and neutrals seperated with my OCPD being at meter pedestal?? Finally he has me supplying PP2 with 3 4/0 XHHW AL from disconnect and a #8 CU ground. Now I know this is not right, should be a #4. I just wanted some input before I respond to engineer with list of issues. How would you tactfully suggest this appropriately to the engineer?
Engineer's Design???
- Thread starter moresi
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Assuming single phase and 1 set of your 300s is a neutral, I see no reason fro the 1/0
Again, if the meter pedestal has no overcuurent devices, I see no reason for the #2
There should be 1 grounding electrode conductor from each service disconnect. They can each be routed seperately to the water or one can be tapped to a common electrode conductor, which in this case should be a 1/0
From the disconnect to PP2 could be a #6 Cu based on 200 amp
Engineer and tactfully..surely you jest
SAC
Senior Member
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- Massachusetts
If you don't think something flies, let them know why you think that. Give the section number, why you think that the plans violate that section, and ask why it doesn't apply. In your post you have a long description, but no references to the code. You'll get better attention from the engineer(s) if you have the code references (if not simply because hat it saves them from having to search the code - if they were to bother to).
That changes things. From your meter pedestal combo, here you would need a a #6 Cu or #4 AL to you disconnect & panel.
Per 250.32(E) the grounding electrode conductor from your disconnect and panel would have to be sized per 250.66. In your case,a #4 cu from each, or a common 1/0 Cu to the water with #4 taps to each disconnect.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I thought you couldn't run two feeders to a home?
- Location
- New Jersey
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- Journeyman Electrician (retired)
Yes the #1/0 from the transformer must come out since it would be in parallel with the neutral and would do nothing. There can only be one supply to the house so the two 200 amp feeders is incorrect. Sounds like the entire setup needs to be redesigned.
I have seen this type of service used on other large homes here in the area where a meter main with 2 - 200 amp breakers is used - pedestal mount - and 2 sets of feeders run to the home. The OCPD at the meter / main is a requirement of the POCO as a means of disconnect. PErhaps it is allowed under 225.30(B)(2).
Correct me if I am wrong but 225.30 limits the number of supplies to more than 1 building on the same property. Th OP has 1 house on 1 piece of property so 225.30 would not apply in this case. What the OP has is 1 service feeding 1 house with 2 sub panels. I don't see the problem with that.
winnie
Senior Member
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- Springfield, MA, USA
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- Electric motor research
I am also comfortable with this installation, in that it is _essentially_ the same as having a meter-main on the side of the house, followed by two feeders to two separate sub panels inside the house.
The technicality that may make it a code violation is that the meter pedestal can be considered a _separate structure_. So if the AHJ interprets things this way, then you have two feeders from one structure to another.
I believe that it makes more sense to consider the meter pedestal to be an component of the house...but I believe that a literal reading of the definition of 'structure' and the requirements for detached structures actually supports the more restrictive definition.
-Jon
Obviously, as Winnie, Cow and Jomaul all point out. Acceptance of this installation in general will depend on how your AHJ looks at the separate pedestal in reference to 225.30.
If the "two feeders" are allowed, the I refer back to my post #5.
If the "two feeders" are allowed, the I refer back to my post #5.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
So even if the AHJ accepted this arrangement based on the definition of a structure and it's application to the meter pedestal wouldn't the two disconnects need to be grouped together at the house? Sounds like the panels are at opposite ends of the house.
Yes, PP1 and a main 200 amp disconnect is grouped together in mechanical room 1 where feeders from pedestal enter. So at this point, as I assumed, we agree that the desing is wrong in including a ground wire running from pad mount xformer to pedestal. It seems to me that design should have two rods driven at pedestal and then 2 sets of 4 conductor cable run to house - 4/0 xhhw Al and #4 CU ground each set. Then at house water pipe ground should be 1/0 CU hitting PP1 and 200 amp disco. I plan on sending this to engineer along with code sections.
sounds good to me, not a fact that will matter.
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