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Need advice on 200 amp underground service


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Have worked on overhead services before but would like to do my first underground service. Here is my plan. Run 2" conduit up pole about ten feet then 2' under ground with 4/0 3 conductor aluminum wire. Then to meter socket on two treated 6x6 posts with 2x8 treated boards between them to mount Meter Main with Load Center. Two 8' ground rods 6' apart within about 2' in front of posts with 4 gauge copper stranded wire going from panel then both ground rods then back to the panel. Have a couple things that I am not sure of though. Does ground wire have to go in conduit or can I just strap it to the service conduit? And do I need expansion fittings where the conduit goes up the pole and up to the meter?

Here is the meter socket and breaker panel I am thinking about using.

Milbank Meter Main with Load Center

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Hi Robert

First off I applaud you for doing some checking before attempting something for the first time. I do wonder if you came to the best place for that. This forum is used primarily by inspectors, and not by electricians or DIYs. There are several excellent electrical forums out there, including Mike Holt's forum, where you can expect to hear a lot more on this question. http://forums.mikeholt.com/

My first question would be why you are bringing this underground. We normally see that only with pad-mounted transformers, not overhead conductors, though I'm sure you must have a reason. Next, the 2 inch conduit would meet the code for your 4/0 wires, but it may have to also comply with utility rules. Here in my part of California, our utility has a minimum 3-inch size for all underground services. Also remember that your 2 feet underground means 2 feet of cover on top of the conduit, not 2 feet from grade to the bottom of the ditch.

If you're going to use 4AWG copper to your ground rods, you don't need conduit for them. You could use 6AWG (even though you have a 200-amp service, grounding electrode conductors that solely serve rods never have to be larger than 6). You still would not need conduit if you ran the conductors onto your posts or strapped to your riser.

You may need expansion fittings on the pole, though most likely that can be avoided with straps that allow some movement. Depending on the slope of the grade and the potential for frost heave, you may need a meter riser slip fitting.

I'm not impressed with that Milbank equipment. Siemens/Murray make some nice meter mains with a separate pull compartment to the left of the breaker compartment.

Finally, your rods will have greater efficiency if they are further apart. 6 feet is the code minimum. 16 feet would be better.

I think you want to do some research with the local utility and building department before proceding. Good luck.

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Have worked on overhead services before but would like to do my first underground service. Here is my plan. Run 2" conduit up pole about ten feet then 2' under ground with 4/0 3 conductor aluminum wire. Then to meter socket on two treated 6x6 posts with 2x8 treated boards between them to mount Meter Main with Load Center. Two 8' ground rods 6' apart within about 2' in front of posts with 4 gauge copper stranded wire going from panel then both ground rods then back to the panel. Have a couple things that I am not sure of though. Does ground wire have to go in conduit or can I just strap it to the service conduit? And do I need expansion fittings where the conduit goes up the pole and up to the meter?

Here is the meter socket and breaker panel I am thinking about using.

Milbank Meter Main with Load Center

My best advice:

Go down to your building department and ask to speak with the inspector who'll be inspecting your work. You'll probably have to come back at a specific time when he'll be there. Ask him for advice.

If you're nice, he'll be a great resource for you.

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Thank you so much for the info. I have been going over the PDF document that National Grid sent me and the NEC but some stuff I just was unsure of. Because they say use an expansion joint for underground service conduit but don't specify if needed on both sides or just one side. The reading and stories I have read about conduit pulled apart seems like a good reason to just go ahead and use them at least at the meter side because of the cold winter and hot summer. The conduit on the pole could be allowed to slide up and down because it will not be fixed to anything. But I will try the other forum for some more info. Some parts I have to go back and fourth and see if their requirements are higher than the NEC. Nothing about the conduit size. But once I have completed my plan I will submit it to them and see what they think.

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As far as National Grid is concerned you and I are in the same region. Surprisingly, they do not require expansion joints at the meter or the pole. It's an excellent idea to install them though, they're very inexpensive.

I you're running PVC, they want schedule 80 at the pole, schedule 40 is ok elsewhere. Leave at least 30' (feet) of the 4/0 URD above the top of the riser the for them to make the connection .

If you don't have a big crimping tool to install the necessary connectors for the meter socket, there is a terminal called a Cytolock that works great with no special tools.

If you call an electrical supply house, they'll probably know exactly what you need to satisfy the utility.

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Yes I plan on using Schedule 80 all the way from the pole to the meter socket. Here inspectors like to see Schedule 80 used on all service cables and all sub panel wire underground.

The document I am looking at from National Grid says it's required.

Even though the meter has hex set screws to tighten the wires I still need to use a crimped connector? Electrical supply let me borrow a crimper last time.

Seems inspectors around here all have their own ideas. Once did some piping inspector failed some PVC pipe said we had to use cast iron. Call and another inspector shows up and said why would you use cast iron.

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The recommendation for going to the local inspectors is the best advice; it's what I always did when I was working in rural areas. The next best place is the local supply house; the good counter guys know exactly what you'll need because they're constantly selling it.

Between the two, you'll probably know most of what you need; you can find the rest.

In the city, you can't do anything fun. Some of the supply houses won't even sell to you unless you're Local 134.

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Thank you to everyone for the great info. I will be sure to use those resources and then double check with national grid by sending them a diagram of everything I am going to do. I really wished the building was permanent so I could do overhead.

Looks like that conduit in your pictures never saw any glue. Usually the conduit glued properly should break when being pulled out. Something that came apart that clean looks line no glue used. I never knew about slip fittings just read about them in the document I got from national grid.

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