I have 2 electrical subpanels to install off my home's service. My home service is 800 Amps. These will be taken as 2 separate runs off my main service box.

The first is for a barn which is 250 feet away and I want to put in a 100 Amp panel.

The second will run to a well house which is 300 feet away. This will power a few things. One is a shallow well pump located in the well house. I want to come off this panel to run 7 post lights along my driveway (Each light has a 150 Watt bulb. 1 light will be at the well house. 2 lights will be spaced 100 feet apart towards my home and the other 4 lights will be spaced 100 feet apart away from the well house in the opposite direction. I also want to have an outdoor receptacle at each post for Christmas decorations. Also, there will be 2 gate motors at the far end of the lights around 350 feet away from the well house (motors are stepped down to 24 V dc.) I am unsure what amperage to place here.

The obvious questions are what size wiring and what size conduit? Anything not obvious I need to look out for? I am confident I can handle the wiring of the panels, etc but the sizes of the runs bother me.

Any help is appreciated.

Thanks

I would use #4/0 URD four wire cable to feed the panel.

Use #2 URD four wire cable to each light post, and to the motors.

If the path is rocky or difficult to lay cable in a bed of sand 6 " below and above, then use 4" DB PVC duct in a two foot to the top of the conduit,trench. If the soil is very rocky, lay a bed of sand above and below the conduit.

If the conduit crosses under a road or drive with heavy truck traffic, trench should be 36" deep.

Lay warning tape the entire length 12" below grade over the conduit.

At each post use a small handhole, 12" x 18" to junction to a smaller #10-3 with ground UF cable to each post. Use 1" conduit into each post. Can you splice in the pole base?

Use a in ground handhole at the panel also to change over to a smaller 2" conduit into the panels.

Be sure to treat the AL cable connections with aluminum rated connectors, anti oxidant compound, and torque the connections.

Hope this helps.

Accurate calculation depends if you have 3 phase service at 208V or single phase at 240/ 120V.

3 phase transmits approximately 3X the power but the conductors will have a greater voltage drop and will be sized larger. Best to know now because if you undersize your supply conductors it will get expensive.

I believe most utilities do not allow single family residential buildings, and most rural areas to use three phase, but certainly something to be sure of.

208 volts will skew the calculations.

But speaking of accurate calculations:

100 Amps at 240 volts single phase = 24000 watts of power

100 Amps at 208 volts three phase = 35984 watts of power

Or doubled the amount of power, at voltage reduced by 13%

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Originally Posted by mkgal4

I have 2 electical subpanels to install off of my home's service. My home sevice is 800 Amps. These will be taken as 2 seperate runs off of my main service box.

The first is for a barn which is 250 feet away and I want to put in a 100 Amp panel.

The second will run to a well house which is 300 feet away. This will power a few things. One is a shallow well pump located in the well house. I want to come off of this panel to run 7 post lights along my driveway (Each light has a 150 Watt bulb. 1 light will be at the well house. 2 lights will be spaced 100 feet apart towards my home and the other 4 lights will be spaced 100 feet apart away fom the well house in the opposite direction. I also want to have an outdoor receptacle at each post for Christmas decorations. Also, there will be 2 gate motors at the far end of the lights aound 350 feet away fom the well house (motors ae stepped down to 24 V dc.) I am unsure what amperage to place here.

The obvious questions are what size wiring and what size conduit? Anything not obvious I need to look out for? I am confident I can handle the wiring of the panels, etc but the sizes of the runs bother me.

Any help is appreciated.

Thanks

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Thanks for the good info. I want to avoid aluminum if possible (even though copper is more $$) to avoid any connection trouble. I had some reliability issues with an older house that had some aluminum coming into copper. How would that affect the wire sizing?

Then 2/0 in place of the 4/0 and still use #2 copper for the other.