How to Run Underground Power to a Shed – This Old House

How to run power to a shed

Powering an outbuilding is probably a job for a pro, from figuring out how many volts and amps a shed needs to knowing whether the current electrical service can give that to excavating a hole for conduit that complies with code.

The electrician from This Old House, Scott Caron, walks us through his process in this video.

How To Run Power To A Shed | Steps to Run Power to a Shed:

Determine the outbuilding’s expected power requirements. Is 120 volts sufficient, or will 240 volts be required? What types of electrical loads can be expected? This defines the size of the feed wire and the new circuit breaker size required at the main panel of the house. The shed requires 240 volts and 60 amps.

Locate the main panel of the house and check to see whether there is enough power coming in to fulfill the needs of the outbuilding and if there is still room to add the new circuit breaker.

The wiring connections are made simpler by adding a subpanel close to the main breaker for the house.

It’s time to dig the trench outside. Scott dials 811, the national Call Before You Dig hotline, before starting an earthwork. In order to prevent damage from digging, this service sends out a technician to find and mark any existing subterranean services. This service is not only free, but it is also mandated by law.

With a trenching machine, it is significantly quicker to dig a trench that is deep enough (for 240v power, code requires the conduit to be at least 18 inches below the surface). However, even this machine can’t pass through ledge or bedrock, thus a subsequent step will be necessary.

The ditch is filled with a few inches of sand to shield the conduit from jagged rocks. It’s crucial to have dug the trench deep enough so that the conduit will be at least 18 inches deep, even with his added material.

Pulling wires will have enough of clearance if 1 12 inch PVC conduit is used. The joints are secured using specialized adhesive.

Heat from a specialized propane torch is used to soften the plastic pipe where gentle bends are required so that it can be bent. The new shape of the conduit is fixed once it has cooled.

The trench has been completely lined with conduit and is protected by a layer of sand. Scott places red caution tape on top of the sand to warn anyone digging here in the future that there is subterranean power.

The conduit, sand, and warning tape are covered with a 2 inch thick coating of concrete in one location where the trencher ran into ledge and was unable to dig down far enough.

The trench is backfilled with the dirt from the excavation after all the conduit has been placed. The excavation will merge back into the lawn with some grass seed, mulch straw, water, and time.

Running an electrician’s fish tape from one end to the other is the first step in getting the wires into the pipe. To know when the fish tape reaches the other end, it is helpful to have a helper in this situation, in this case the homeowner.

Scott threads the fish tape through the conduit, fastens a piece of 14 inch rope to the end, and then pulls the rope back to the opposite end.

Code mandates the use of separate conductors rather than sheathed cable in conduit (typical house wiring where two or three conductors plus a ground wire are wrapped together in an outer shell). Two 120v conductors, one neutral, and a ground are linked to the rope in this instance and hauled into the conduit because it is a 240v circuit. To supply the necessary 60 amps, all the wires are heavy, 6-gauge.

The conduit is attached to a junction box inside the shed at the point where it passes through the wall. Since it is simpler to run the cable within the shed to the new sub-panel, the individual wires from the conduit are connected to the same gauge non-metallic sheathed cable. Special connections with screw-clamps are utilized with this heavy-gauge wire.

In contrast to the main panel in the house, where they hook together, the ground and neutral terminals are separated in the sub-panel. The ground terminals are connected to a separate ground rod that is buried outside the shed.

One hot wire is connected to each bus bar, while the ground and neutral wires are connected to the appropriate terminals.

The subpanel is equipped with breakers and a surge suppressor, and the shed is wired using conventional interior wiring methods.

Just like it was done at the shed, the wires from the conduit are connected to wires from non-metallic sheathed cable in a junction box at home. The connection continues from there to the new panel, which was put in place below the primary panel that was already there. The shed can now be powered up thanks to the installation of a 60 amp, double-pole breaker.

When the work is finished, the shed will have outlets, inside and exterior lighting, and is prepared to accommodate an eventual electric vehicle charging station.

Tools

Reminder: If you need to move a lot of earth and a shovel is insufficient, think about renting a gas-powered trenching machine from Home Depot.