Installing Sub Box/Running Power

Old 10-18-15, 09:40 AM
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Installing Sub Box/Running Power

To start off, I am not an electrician, hence why I am asking everyone here. I enjoy learning and electricity isn't completely foreign but don't know enough to get my job done without help.

I just had a 30x30 shop build about 150ft from my house. I just installed a sub box in the shop.

4 outlets, and thinking of installing 6-8 8ft light fixtures.
items to be used in shop
110v mig welder
air compressor SPEEDAIRE 2 HP, 30 gal. Horizontal Splash Lubricated Tank Mounted Electric Air Compressor, CFM: 4.9 - Stationary Electric Air Compressors - 4B234|4B234 - Grainger Industrial Supply
In the next few months I will be installing a car lift so I will need 220 for it.
3 HP 220V +/- 5% (209-231volts) single (1) phase. A 30 amp breaker is required.
Basic tools usually found in shops.

Now here is what I am thinking will work "not sure if it will". Suggestions Appreciated
(3) #6 stranded common/powers
(1)#10 Stranded ground

What size conduit should I use? What kind of conduit? How deep to burry? It is a clear straight shop from the back of the Main Box to my shop. Cleared Back yard.
Old 10-18-15, 09:57 AM
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Welcome to the forums.

Based on #6 THWN copper wiring you would end with a 60A subpanel. You would use a 2P60 breaker in your main panel. You could use 3/4" PVC to run that line but it may be tight. I would recommend 1" PVC conduit buried 18" below the surface.
Old 10-18-15, 10:25 AM
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You should use at least a 12 space (20 might be better) 100 amp main breaker panel for your 60 amp subpanel. That way the 100 main breaker serves as your code required disconnect and you have space for several circuits. You will need to add a ground bar to the sub panel and need a ground rod at the shop. Ground rod id connected with #6.
Old 10-18-15, 07:06 PM
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Workshops have a tendency to need more power as time marches on and for that reason I would at the very least make it easy to apply future upgrades. To that end I would use nothing less than 1-1/4 inch PVC electrical conduit. Schedule 40 will be sufficient for the straight underground portion but for the bends and risers at the point where the conduit enters and leaves the earth I would opt for either intermediate (IMC) or rigid (RMC) metallic conduit. The reason for the metal is that on a long pull the conductors (or even the pull rope) can literally cut through a PVC bend. Also, the if the portion above ground is "subject to damage", a somewhat subjective condition that will be determined by the inspector, the use of schedule 80 PVC is usually seen as a minimum. So much easier to just run the metal conduit in the beginning.

You don't need threading tools for the metallic conduit, just use compression adapters made for rigid conduit. They are not always stocked by the big box mega-mart homecenters but they are readily available from electrical supply houses. You shouldn't need but one length of the metallic conduit and you can cut from each end thereby having to use only two compression adapters. Use factory bent elbows unless you have the means to bend the metallic conduit without kinking it. I personally would bury the conduit with a minimum of 24 inches of cover over the top of the conduit, especially if you will have vehicle traffic over the conduit.

At 150 feet (actually more if you count the risers) you need to consider voltage drop. For minimal amperage draw, a few lights and either the welder or compressor the #6 conductors should be ample. However, as I previously stated, the electrical needs of a shop are likely to grow over time. I would consider upsizing the conductors to #4 with a #8 for the equipment grounding conductor if you are using copper conductors and increasing to #2 and #6 respectively if you are using aluminum. For the panel in the shop I would suggest at the very least an 8-space, 16-circuit main breaker panel or the 12-space panel that Ray recommended.

When you buy the wire DO NOT scrimp on the length. Add in the horizontal distance from each riser to the height to the top of each panel and then add a minimum of five feet at each panel for bending and connecting. The last thing you want is find that you are a foot short on one end. Better to toss five feet of extra wire than to have to add a junction box, splice and then add another couple of feet of wire.

Note well, these are just the bare minimums of instructions. There are a lot of details that have been omitted.

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