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Old 05-20-2016, 01:28 PM   #1
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Main Service panel grounding question


I am building a house and have a question about the feeder to the house
I have a remote meter with 2 200amp service breakers (One is for the house and one is for future workshop)
I have a 2 underground conduit run from the meter to the house panel. The distance is 115feet (actual cable length)
I am reading the NEC 1310.15 and I think I need 2/0 copper or 4/0 Aluminum service feeder. I also think I need SER cable to provide the two conductors and the neutral.I am not sure if the table still applies, as it does not include a distance requirement.
The meter-can and adjacent disconnect panel which also powers the Well is grounded with ground rods and the house panel is grounded to a concrete encased rebar electrode.
Questions
Confirm feeder size for 200 amp service and type for use in 115 feet of underground conduit.
Grounding Question
Do I need to use the ground wire (in the SER bundle) to connect the main disconnect at the meter and the House panel? This would Creating two ground paths in the system. Or just simply not connect the ground wire and have both ends separately grounded (ground rods at the meter and House to foundation ground).Or should I disconnect the house ground completely and use the ground at the meter 115 feet away.
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Old 05-20-2016, 01:43 PM   #2
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Re: Main Service panel grounding question


First, SER cannot be used underground . Second, you need a 4 wire feeder between the disconnect and the house.
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Old 05-20-2016, 01:52 PM   #3
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Re: Main Service panel grounding question


SER can not be used in a conduit underground? I thought it was rated for wet location.

4 wire feeder? two for load, one neutral, and ? (ground?) thus my grounding question.

what cable is then needed if not SER, I cant use SEU if I need the neutral and ground right?
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Old 05-20-2016, 01:55 PM   #4
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Re: Main Service panel grounding question


You will use individual conductors in the conduit..
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Old 05-20-2016, 02:09 PM   #5
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Re: Main Service panel grounding question


thank you,
it is quite expensive so am trying to make sure I understand and do it once correctly. SER is shown as XHHW-2 so I had assumed I could use it in conduit, but I may have misunderstood it.

the OP asked a couple questions and you have answered one (cable type) The gauge is 2/0 copper or 4/0 alum based on the table, right? voltage drop does not apply significantly at 115 feet?

You are saying I do need to connect the ground wire between the two panels and have 2 separate ground paths? (the 4th wire) if so does it need to be the same gauge?

Last edited by KirkJT; 05-20-2016 at 02:33 PM.
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Old 05-20-2016, 02:33 PM   #6
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Re: Main Service panel grounding question


You need to discuss your project with the local wiring inspector to make SURE you fully understand their interpretation of rules in your area. In my town, the local rules differ slightly from NEC.

Your house panel would be treated as a subpanel under NEC, since the main disconnect is at the meter, based on your description. This means, as Jim Port mentioned, that you need four wires for U.S. service, two for the hots, one for the neutral, and one for the ground. In my jurisdiction, subpanels located in a separate building require independent grounding from the main panel, which would mean two grounding rods, but possibly you could use the UFER system you described at the house instead of the rods.

As to the SER cable you mentioned, you would normally pull independent wires through conduit, as pulling cable (which is an assembly of wires) would be difficult. One of the electricians on here can help you understand what size wires you need, in my town I think the ground is generally one size smaller than the hots and the neutral, but this may vary with jurisdiction.
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Old 05-20-2016, 05:06 PM   #7
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Re: Main Service panel grounding question


looking through options; Since SER cant be used underground, I would pull THHN ? XHHW-2? or URD? The panel is 12 feet inside the house from where conduit enters the crawl space and conduit comes into the Panel direct form the meter. not sure I can use URD either in this case? as it would be inside the home?

Last edited by KirkJT; 05-20-2016 at 05:11 PM.
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Old 05-20-2016, 05:13 PM   #8
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Re: Main Service panel grounding question


The URD cannot be used inside. However , I think there is a dual listed URD/USE that can be used.
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Old 05-20-2016, 05:45 PM   #9
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Re: Main Service panel grounding question


thanks I think I am getting closer
while I have not found the dual rated UFD/USE option
I found at the supply house USE-2/RHH/RHW-2

so I would be able to pull 4 of these to make up the run?
as it can be used underground, in conduit, both inside and outside the building envelope.
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Old 05-20-2016, 07:33 PM   #10
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Re: Main Service panel grounding question


but can I pull 4 4/0 in a 2 inch conduit
or do I need to go with copper 2/0 to get 4 in a 2" conduit
looking at the IRC and not sure
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Old 05-20-2016, 08:09 PM   #11
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Re: Main Service panel grounding question


The ground should not need to be 4/0.
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Old 05-20-2016, 10:22 PM   #12
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Usually #6 copper or #4 aluminum is the minimum size for the grounding conductor on a 200A feeder*.

You'll need to investigate voltage drop as it's not an NEC required calc.
IMO you're not going to need to up size due to voltage drop but don't take my word on it.

*If you do increase conductor size to compensate for VD you'll need to up size your grounding conductor.

I can't imagine a jurisdiction allowing a three wire feed in this case but it should be a simple call to find out.

A four wire feed is not double grounding as someone in this thread is suggesting.

Your house will be considered a separate structure according to the NEC and will require it's own grounding electrode system. The GES serves a different purpose than the grounding conductor from your service disconnect.
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Old 05-23-2016, 01:48 PM   #13
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Re: Main Service panel grounding question


Now I have a new dilemma related to the OP.

I bought a 200 amp Plug-on-Neutral Panel from Eaton with all the associated breakers.

Since my service is a 4 wire and not 3 wire as I had originally assumed, how do I separate the Ground and Neutral bars on this panel to now make it work as a subpanel?

I am guessing, though could be seriously incorrect, that I don't separate the neutral bridge since the all the breakers need this to work (not even sure it can be removed) but would add a new but separate ground bar?
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Old 05-23-2016, 02:55 PM   #14
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Re: Main Service panel grounding question


Quote:
Originally Posted by KirkJT View Post
Now I have a new dilemma related to the OP.

I bought a 200 amp Plug-on-Neutral Panel from Eaton with all the associated breakers.

Since my service is a 4 wire and not 3 wire as I had originally assumed, how do I separate the Ground and Neutral bars on this panel to now make it work as a subpanel?

I am guessing, though could be seriously incorrect, that I don't separate the neutral bridge since the all the breakers need this to work (not even sure it can be removed) but would add a new but separate ground bar?
The bars on both sides of the box are to used as neutrals. You have to add an additional bar or bars for the ground.

There are raised threaded nubs on the tub for mounting.
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Old 05-23-2016, 02:57 PM   #15
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Re: Main Service panel grounding question


thank you
that makes sense.
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