Trying to find out if this possible and within code. I have a detached garage which has a 100 amp subpanel it it. 60 amps are being utilized by the garage, lights, receptacles, and at one time had a heater and 220v dryer connected. Dryer is gone and heater is too. I need to know if I can run a feeder 120v line to the garden shed from this subpanel in the garage as opposed from the house main power panel which is father away and more painful to connect. The hobby/garden shed has a 40 amp subpanel installed already.

Short answer... yes you can. You will need to run 4 wires though, separate the neutral and ground, and isolate the ground. (this should already have been done at the already wired existing sub panel) You will also need a ground rod at the garden shed. (4 wires allows you to have 240v at the shed, which is much more practical) You can run #8 wires for the panel for the 40 amp service... unless the distance is too great. Care to elaborate on your project?

The garden/hobby shed is about 110' from the garage and it's a straight shot to the sub-panel. This would be easier install since the house main power panel is on the opposite end of the house and would require the run to go through the crawlspace or around the perimeter of the foundation. On the outside of the garage, wall closest to the shed is already a electrical conduit containing the main feed from the house to the garages sub-panel. I was planning on using a new conduit next to this one for the feeder to the shed... not sure about the code on this though. I was trying to figure the Voltage Drop Indicator so I could determine the wire size necessary. Here is the formula: VDI=Amp size of Circuit Breaker X Feet / Percent Voltage Drop X Voltage. My VDI comes out to 13.7 which when compared to the AWG/VDI comparison table the gauge is off the chart, not small but large... like 000 gauge. Must be doing something wrong but have not found it yet. Back to the formula, AMPs is the Amp size of the circuit breaker(my case 40 amps), Feet-total length of wire needed(for me 113 feet) Voltage-amount of voltage needed for the device or device(my case 110v) The percent voltage drop is the national standard average of 3%. I was planning on using UF-B wire, gauge 6 or 8... got this from using some the online electrical calculators. I had not planned on encasing the wire in conduit for the run only at each termination point... was going to bury it a good 18-24 inches. Any help you can give would be appreciative, thanks.

Try this calculator:


Wire Size Calculator

You should be able to use #8 for a 240 line at that distance... but you certainly could go up to a #6. My advice... put the individual wires in conduit, metal or pvc. It will make things simpler for you, and if your needs change you will easily be able to upgrade to a larger wire. The trench is the hardest part, the conduit will be a relatively cheap part of the installation. Unprotected buried cables will fail if a nick happens to penetrate the insulation and the conductor gets wet.