[amiteman]

Hi,
I recently posted a question that probably wasn't specific enough about my situation. Please bear with me as I am a novice.
I have a 3600 sq. ft. metal building in which I plan to put a 2400 sq. ft. workshop ( general shop for woodworking and metal work) and a 1200 sq. ft. all electric apt.
The local power co. told me that I couldn't get a 400 amp service without a detailed amp load list for the building. I'm really not sure of the load demand so they gave me this option. I can put in a 320 amp single phase meter pan. (3 phase not available in my area) All copper cable will be used.
This is my plan. I'm going to run 500MCM from the service head through 3" rigid through the 320 amp meter pan to a 12" X 12" X 48" wiring trough. From out of the trough , through 2" rigid, 3-0 cable to a 200 amp fused disconnect for shop area and a 200 amp disconnect ( fused for 175 amps) for apt. area. The 3-0 cable will continue through to 200 amp shop service panel and 200 amp apt. panel both inside bldg. All of this will be grounded with a 1-0 wire to two 5/8" X 8' ground rods set 8 feet apart. I am unsure about how to run the ground wire.
Does all this sound practical or is there any overkill on cable sizes. I'd rather be on the safe side of safety and any future upgrades. Thanks Mr. TK Russell for answer to my previous question concerning cable size to 320 amp meter and 200 amp service.

[tkrussell]

Everything you outlined is exactly correct, and I see you noted this is not a residential service, and your wire sizes are correct.

I have a few questions and comments:
What is the distance of the interior portion of the 200 amp feeders from the trough to disconnects? This distance of interior service lateral must be kept short as possible, most inspectors and utilities allow up to 10 feet, but only if adequately protected.

If the grounding electrode conductor only connects to ground rod(s), then #6 copper wire is allowed, NEC 250.66(A). This can be run in PVC conduit from the point of connection to the grounded conductor (neutral). This connection can be at the connection of all the neutrals in the trough, or in the meter if allowed by utility or local code.

Also, since the building is all metal, it must be considered as a grounding electrode, here is where you must use #1/0 copper. Again this can be run in PVC conduit where exposed, usually the entire length if exposed in an open steel building. If a steel I-beam is close to the point of connection to Neutral, can be open wire tyrap or strap as needed.

From the two main breakers, the feeder now must have an equipment grounding conductor, if pulled in conduit, use green #6 for both feeders along with the two hots and one neutral. Keep the connections of both separate in the panels.
If the water is utility with metal pipe, then it also must be considered as a grounding electrode no than 5 feet in from the street, and need #1/0 connected to it, jump out the water meter with the ground wire. If the water is metal and well, bond it the equipment ground from a panel to anywhere on a cold water pipe.

The feeder for the apartment may be #2/0 since it is residential.

That's all I can offer for the moment, hope it helps.

[amiteman]

Dear T.K Russell,
The two 200amp disconnects, ( Shop 200 amp fused ) and ( Apt. 200 amp fused for 175 amps ) will both be connected to wiring trough right below 320 amp meter pan. The Shop disconnect will go directly through wall to interior 200 amp shop panel. The Apt. disconnect will go through wall to 90 degree condulet elbow and feed will travel some 60 feet or so to Apt's service panel. I hope I answered your question correctly.
Thanks again for all your help,
amiteman