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Conduit and Commercial Electrical Rough-In A mobile classroom is wired for electricty. From "Trade School" episode DTRS-205

Figure A

In this segment, electrical student Jerry Harper participates in a class "rough-in" project for a mobile classroom building (figure A).

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Basic Tools:

tape measure
power drills
pliers
screw-tight connectors
conduit bender
hacksaw
reamer
couplers
pipe straps
wire
electrical tape
wire cutters
wire strippers
wire nuts
mud rings
box plates

Figure B

The classroom is completely framed, but does not yet have any insulation or drywall. One noticeable difference between this commercial project and a residential one is the installation and use of metal piping, called conduit (figure B).

After discussing the game plan, instructor Ted Topoleski divides the class into teams of two and assigns each a circuit to wire. Jerry pairs up with his classmate Barry, and they begin by installing the metal junction boxes for their particular circuit.

Referring to the engineer's prints, Jerry measures and marks along the framing and installs the boxes flush with the studs and rafters using a power drill (figure C). Since the boxes are made of metal, and therefore conduct electricity, Jerry screws in a green ground-wire pigtail to the back of each box (figure D). Next, Jerry attaches screw-tight connectors inside the removed knockout hole (figure E). Later, these connectors are used to secure the conduit to the junction boxes.

Figure C

Figure D

Figure E

	Figure F
	Figure G

In most commercial installations, electricians work around aluminum framework that might include pre-fabricated portals for conduit. But because this classroom is framed with wood, Jerry bores large holes through the top plates of the walls to support and contain the conduit. He lines up these holes directly above each installed box and drills using a heavy-duty power drill (figure F).

A network of conduit connects all the junction boxes and the main panel together, which serves to protect the wires that make up the circuitry for the building. Bending it is more complicated than it may appear.

To join a wall to a ceiling box, Jerry first positions one end of the 10 foot section of conduit to the connector and, in this case, estimates an offset bend that will angle the pipe toward the nearby stud, and then angle again vertically up to the stud (figure G). More experienced electricians might use trigonometric formulas to devise the exact angles. According to code, the conduit must sit against studs or joists so that it can be strapped within 12 inches of the junction box. The other end will be fed through the hole drilled earlier, and needs to be bent at a 90 degree angle.

Jerry marks on the pipe where he'll need to create the bend, and then fits it into a bender. The bender has markings to indicate the angle (figure H). Jerry forces the conduit against the bender until achieving the desired angle, and then repositions the conduit to make the next bend. With the section of conduit formed, he hooks the top end through the hole in the top plate (figure I) and secures the bottom end in the junction box connector (figure J).

Figure H

Figure I

Figure J

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