multiple sub panels

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  #1  
Old 08-01-15, 07:14 PM
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multiple sub panels

hi all

I have landed pg&e (local electric utility) on a pump shed. I could only get 200 amps max using secondary extension in this location.
I will next supply 2 homes under construction from this location, bringing 200 amps to a garage and then splitting from there to supply both homes with 100 amps.
One home will get an additional sub panel as it is very spread out with one wing over 50 ft from the main sub panel location. I will use 4/0 cu for the first run as it is 250 ft. from there I will run 1/0 to each home, 100 ft and 250 ft removed from the first sub panel. Question... can I reduce the neutral size in any of these feeder circuits? All subs will have ufer grounds and I am assuming that all panels will share a continuous running ground wire and unbonded neutrals.
What is the best wire to use for the ground, solid or stranded? Will solid bare pull ok at these distances? I will oversize conduits (pvc) for ease of pulling.
I've done quite a bit of this work, but always looking for tips and advice.
Thanks
 
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Old 08-01-15, 10:14 PM
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Welcome to the forum.

I have landed pg&e (local electric utility) on a pump shed.


Just to touch on a few points.

A ground wire in a conduit must be insulated and I'd recommend using stranded.
4/0 aluminum wiring is what is used for a standard 200A service. Now you're extending that 200A service 250'. You're going to need go larger to reduce voltage drop.

Other comments will be added.
 
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Old 08-01-15, 10:48 PM
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The sizing rules are going to change since the feeders are not serving the entire load of the dwelling.
 
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Old 08-02-15, 08:20 AM
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If it was me I would use direct burial cable/wire rather then pull that wire, that far, through conduit. You will be digging anyway, what's another 6"? Then only need to use PVC for the risers.

I would also suggest using aluminum for your conductors rather then copper. This will save you a boat load of money, and will be easier to install. I would also do a real load calculation to determine the load on the service. This will better help properly size your feeder(s) for voltage drop. 4/0 copper sounds overkill to me.
 
  #5  
Old 08-03-15, 12:21 PM
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Yes. I figured 4/0 copper would land me at under 3 % drop. Stranded ground it is. Maybe I'll order green for clarity
 
  #6  
Old 08-03-15, 12:26 PM
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Db aluminum conductors will save $$ until a nick turns into a beach ball of bloated white corruption. Swore it off years ago
 
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Old 08-03-15, 12:29 PM
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Copper usually runs about 2-3x the cost of aluminum, even given the conductor upsize required when using aluminum. It is common to use green tape to mark large conductors as ground instead of special ordering green.

If you do go with conduit, use no smaller than 3" at that distance. Install a heavy pull rope or braided tape (no string!) and ideally use steel sweeps. At that distance and weight of the cable, PVC sweeps will erode through during the pull. A quazite pull box in the middle of the run wouldn't be a terrible idea either.
 
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Old 08-03-15, 12:35 PM
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I have 3 inch on the job. The steel bends is a great idea!!
There isn't a great place for a pull box and the conduit will run at about a 15 % grade downhill which should help a little. I will use a 5/8 poly rope and a mule to crank it in. Probably prove the pipe with a mandrel first as well so no problems mid pull
 
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Old 08-03-15, 12:51 PM
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Testing the pipe is a good idea, of course lots of pulling lube too. Just prior to pulling the cable you can pour some big glugs of lube into the uphill entrance of the pipe and pull a foam sponge ball through to spread the lube out in the pipe. Then also lube up the conductors with a barbeque mop as it goes in the pipe while your helper pulls from the other end.
 
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Old 08-03-15, 03:53 PM
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Thanks for the help ibpooks
 
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Old 08-04-15, 08:12 PM
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I figured 4/0 copper would land me at under 3 % drop
At what load?
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Old 08-05-15, 07:55 AM
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Things are changing daily in the house design. Now at the last minute a tesla car charging station was added
I'm bumping 170 amp draw for both houses, pumps, charger. Locked in at 200 from utility as they wanted 50 to 60 k to bring primary up for higher ampacity . first house is 750 ft from power pole and second house is another 230 ft farther. Owner says no poles in his meadow. I need to keep the first leg of 250 ft as hot as possible or the second house will have marginal voltage.
 
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Old 08-05-15, 09:28 AM
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They can afford a Tesla pushing $100K and skimping on the power design?
 

Last edited by Tolyn Ironhand; 08-05-15 at 03:40 PM. Reason: added "K"
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Old 08-05-15, 03:43 PM
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I will use 4/0 cu for the first run as it is 250 ft.
first house is 750 ft from power pole and second house is another 230 ft farther.
You are changing your distances. Now you are 750' away from the pole rather then 250'?
 
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Old 08-06-15, 07:11 PM
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The 750 is from the pole. I brought power 500 ft from pole to meter with utility company. Just explaining the layout. I now have the 250 ft from 200 amp meter to the house to install
 
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Old 08-06-15, 07:15 PM
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This is a single old guy who drives an older Prius He has clients who will meet him in this remote location for business and visits. Budget is set,fixed, and tight . Just trying to make it work.
 
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Old 08-06-15, 08:08 PM
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Budget is set,fixed, and tight
Then buy aluminum direct burial and spend about 1/2 on the wire, also eliminate most of the cost of the 3" PVC conduit and labor. 350 MCM AL will cover your voltage drop requirement.
 
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Old 08-07-15, 07:17 AM
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Agreed. This has got heavy direct burial aluminum written all over it. Backfill with 4" of pea gravel if you're really worried about a stone puncturing the cable.
 
  #19  
Old 08-07-15, 08:31 PM
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I'm slowly coming around you guys
The direct burial sure would be easy.
And AL wire fixes my budget. Trench will be shared with 2 water lines and a propane line but I can put the wire way down and separate the services by a foot
Is p gravel better than sand?
Most of our gravel is crushed and sharp because fish and ge shut us out of the waterways 15 years ago
We have red lava sand which is pretty cheap and really shows up when you get near utilities with a dig

Thanks for the ideas. Finally got a permit today to hang a meter base on a pump house. California. Three weeks when it should be issued over the counter. Now I'll get inspected and pg&e will schedule their work a month from the sticker date. All told an eight week process. Patience is pretty much used up. The crew will really be glad to get away from generators
 
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Old 08-10-15, 08:23 AM
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Whatever backfill you can get cheapest that is smooth / soft. Pea gravel is the choice around here, but sand sounds reasonable too. Check with a local concrete ready mix vendor to see what aggregates they can deliver.
 
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Old 08-10-15, 08:32 AM
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I would use sand.
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