Subpanel on 300 ft run....

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Old 10-20-15, 06:14 AM
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Subpanel on 300 ft run....

Hello, I am trying to convert a barn into a mechanic shop, not commercial, just for me. I plan to run a car lift, air compressor, lights and receptacles, and probably an arch welder along with smaller other tools that can be plugged into the receptacles. I know at some points I will have to hire an electrician and stay within codes but I want to do what I can to keep the cost down. This is what I got.....

I have a 100amp metered subpanel in my main home. We use to use this for major appliances on a time delay for off peak hours to save money....That got old fast. The time delay was deactivated and the appliances were switched over to the main 200amp panel so the sub panel is still hot but not in use. I was going to get an electrician to upgrade this to a 125 amp panel and use it for the power supply to the new shop which is 300 feet away. I think I can save money by digging the ditch myself and purchasing the run wire between the main house and the shop. I will then have an electrician to connect the wire to the 125 amp subpanel and connect it to a new 125amp subpanel in the new shop. I know this wire will have to be 24" deep. A few questions....
1) Is this project doable?
2) What size wire would I use for the run to accommodate voltage drop? I was thinking 1/0-1/0-1/0-2? I know it will have to be underground feeder cable. It would be aluminum cable.
3) In sand/gravel conditions, will I have to put this 300 foot feeder cable in a conduit?
Any help would be appreciated.
 
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Old 10-20-15, 06:41 AM
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The 1/O-aluminum cable will support 100 amps at 240 volts at 3% voltage drop here. You would want 2/O cable for 125 amps.

Direct burial cable can go in any soil conditions. A layer of sand is recommended to give additional protection in case of frost heaves or minor earthquake.
 
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Old 10-20-15, 07:04 AM
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Thank you Allen....currently the sub box at the main house is 100amp, do you think I am doing overkill by going to a 125 amp box for this project or would 100 amp be sufficient? If I did not have to have that swapped out it would save me some bucks. The heaviest thing that would be run in the shop is the arch welder on a 50 amp breaker. The car lift will only require 20 amps, the air compressor 20 amps, and of course not everything will not be running at the same time. Would I get away with 100 amps? I know once I bury the cable I am committed.
 
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Old 10-20-15, 10:03 AM
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I know at some points I will have to hire an electrician and stay within codes but I want to do what I can to keep the cost down
Is it your plan to run the wire and then call an electrician ?
As an electrician I wouldn't make those connections. I'd recommend contacting an electrician first and working with him.
 
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Old 10-20-15, 10:53 AM
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No, I will have an electrician out before I even buy anything but I need to know exactly what I want before I get him out here. I suspect that he will not touch it unless he can see the wire in the ditch to ensure it is up to code. Right now I am in the planning stage so I know how much this is going to cost me but there are some things I can do myself. I do not need to pay an electrician to dig a ditch and can purchase most of the materials myself to save....all I need is his skill for a half a day to hook it up. Before the ditch is filled in I would also need it inspected by the county. I plan to do it correctly but am wandering about the 100amp vs 125amp options. It would cost much more to convert to 125 amp but if I really don't need it for a hobby garage I would just stick to the 100....I am not sure. I would just like to make an informed decision when the electrician is out here rather than just rely on his one opinion. I am not going to be running a lot in the garage and the biggest thing would be the 50amp arch welder.
 
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Old 10-20-15, 04:49 PM
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all I need is his skill for a half a day to hook it up. Before the ditch is filled in I would also need it inspected by the county.
So, who is getting the permit for this work?

Direct burial cable can go in any soil conditions
If the soil is rocky, direct burial cable will last a few years before a rock penetrates the insulation. If it is rocky, I'd use PVC conduit and separate Type XHHW conductors rather than trying to pull direct burial cable into conduit.
 
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Old 10-20-15, 05:18 PM
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The 100A supply is fine for your garage. Save the money by not increasing the size there and put it into the PVC conduit and even up-sizing the wire size.

I'm a fanatic with long distance services. I always run larger wire than called for to reduce sagging on high current demands.
 
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Old 10-20-15, 06:02 PM
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Thank you for all the info. The electrician will have to apply for the permit, that is just how it is done. I just can't see him doing all the mule work. My hope is, if I can make it happen, to put a chunk of change in his pocket for an easy breezy job while keeping a chunk in mine.
 
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Old 10-20-15, 07:48 PM
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I agree..... just keep him in the loop. There is more than one way to do your job. If he doesn't approve it could cause a problem.
 
 

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