Rough Wiring for Home and Office: Setting Boxes

You should now be ready to start installing the electrical system you carefully planned in the previous section This process begins with the rough in, as the first stage in wiring a new house or addition is called, and it involves mounting the outlet boxes, running the cable or conduit and wires, and locating the service equipment in the stud walls and ceiling joists before they are covered with finishing materials. A knowledge of how and why this work is done is helpful even for those who won’t actually perform these tasks because it provides a basic understanding of the physical structure underlying an electrical system.

The electrical service can be installed anytime after a house or addition is framed up and closed in without creating problems. The electrical rough in could also begin at this time, but it's customary to wait until after the plumbing and heating have been roughed-in to make these basic electrical installations. After the electrical, plumbing, and heating rough ins have passed inspection, the walls are insulated and finished.

Running cable and setting boxes can quickly become tedious if you are doing a large wiring job, but it’s imperative that you be methodical and careful and review all your work before the walls are closed.

SETTING BOXES

The NEC requires that all wiring in the home be enclosed in a box wherever it connects to a receptacle, switch, or light fixture or where splices are made. So you start the rough in by mounting the boxes for these receptacles (shown in your floor plan) on the exposed studs and joists.

Marking Box Locations

Few hard-and-fast rules govern the setting of boxes, but they should be mounted at the same height throughout the house or addition. Standard heights are to the top of the box, 16 inches up from the floor for receptacles and 48 inches for wall switches. Boxes for wall bracket lights are usually about 6 feet above the floor. Using your electrical plan as a guide, mark the side of each stud to which a box will be mounted, at the correct mounting height. To story pole as a marking gauge:

Take a 48-inch piece of 1 by 2 and mark 16 inches up from both ends with a horizontal arrowhead, with the point at 16 inches. You can now position the stick and mark the studs quickly and repetitively.

Switch boxes installed be side doorways must be far enough away from the opening to allow for some space between the door casing and the switch plate. If necessary, you can use blocking to gain the required space.

The face of most boxes should be flush with the finished wall. Set switch boxes tend into the room beyond the stud or joist a distance equal to the thickness of the finished wall or ceiling. Square boxes are the one exception to this rule. They should be mounted with their fronts flush with the framing. When the mud ring is attached, its opening will be flush with the finished wall.

Many boxes nail up to the sides of the studs with large captive nails that do not pass through the interior of the box. Instead, the nails pass through extensions at the top and bottom of the box. This system provides a solid installation. Other boxes rely on integral metal brackets for mounting. The brackets are set back from the front of the box enough to allow for the thickness of common wall materials, such as wallboard and paneling, so you can set the front bracket flush with the front of the stud with out measuring. Drive a couple of shingle nails through each bracket for added support.

36 Roughing-In Cable and Boxes: Box for ceiling fixture; Receptacles; Receptacle; GFCI receptacle for exterior use be enclosed in a box wherever it connects to a receptacle, switch, or light fixture or where splices are made. So you start the rough in by mounting the boxes for these receptacles (shown in your floor plan) on the exposed studs and joists.

37 Common Measurements for Outlets and Switches: Story Stick

1. All outlets must be grounded.

Mark the position of the switch or outlet box on the stud to which it will be nailed.

2. Careful planning ensures that all receptacles on 1 floor or in 1 room aren't connected to 1 circuit. In a kitchen or work area, the outlets above the counter must alternate between 2 small- appliance circuits so that adjacent receptacles aren't on the same circuit. The Code allows up to 8 outlets on a circuit, but local regulations vary—be sure to check the code in your area.

3. Any wall 4’ or more wide must have at least 1 floor outlet. Any wall wider than 12’ must have at least 2 outlets. Floor outlets should be no more than 12’ apart.

4. Floor outlets should be between 12” and 18” above the floor.

5. Any work-counter area up to 4’ wide must have a receptacle above it; over 4’ wide must have 2 outlets. Work-counter outlets should be no more than 48” apart.

6. Work-counter outlets should be 8” above the counter.

7. Light switches must always be on the same side of the door as the doorknob.

8. Lights in stairways, hallways, garages, and most rooms with 2 entrances should be controlled from at least 2 locations using 3-way or 4-way switches.

9. Light switches should be between 44” and 48” above the floor or 8” above a work counter.

Choosing Boxes

Boxes come in a number of shapes and sizes to accommodate particular functions and permit a specific number of de vices and wires to be enclosed in them. Metal and plastic boxes are available, and to a certain extent they are interchangeable because they and the switches and receptacles used in them are standardized. The shape of a box suggests its function. (Note that in this book the term plastic includes a variety of nonmetallic materials such as Bakelite, vinyl, and plastic.)

Based on the sidebar and the illustration, select the appropriate box type for each purpose and location in the house. After you have determined which shapes you need, you must choose sizes that are large enough to accommodate the number of wires and devices to be located inside them. The rules for making this selection changed with the 1990 NEC. Generally, larger boxes are now required because of concern about providing sufficient space to accommodate GFCIs and dimmer switches. The sidebar shows the maximum number of wires permitted in a box according to wire size and box volume, which is stated in cubic inches. All boxes, mud rings, and surface-mount device covers are marked with their volume in cubic inches to help you calculate the permissible number of wires quickly. Here’s how it works.

Each wire entering a box, except for the grounding conductors, requires space within the box based on its size. Each No. 14 wire, for example, re quires 2 cubic inches of free space within the box; each No. 12 wire needs 2.25 cubic inches; each No. 10 wire, 2.5 cubic inches. The sum of these volumes largely determines the box size needed, but other factors also apply. Additional space equal to one wire must be provided for grounding conductors if one or more are present in the box, and space equal to one wire is added for each internal cable clamp, fixture stud, and hickey. Each mounting yoke or strap containing one or more switches or receptacles requires space equivalent to two additional wires. To determine the volume required for each of these additional items, use the largest wire size in the box. Include everything to determine total volume available or required.

To summarize, your choice of box will depend on several factors, including: how the box will be used (junction box, light fixture, switch, receptacle, and so forth); how it will be mounted (against a stud, between joists, on a wall surface, in a tight space); how many switches or receptacles it will have (double gang, and so forth); how much volume is required for the size and number of wires it has; and any special requirements, such as supporting a ceiling fan or out door installation.

Metal versus Plastic Boxes

Traditionally, electrical boxes were made of galvanized steel. Purists still prefer the metal box, but plastic boxes have largely replaced metal boxes in new residential construction. Both types of boxes have advantages.

Metal boxes must be used with metal conduit and cable systems. They may also be used with nonmetallic cable systems. Either way, they must be grounded. Grounding is achieved via the conduit or metal cable jacket, or by the grounding conductor in the nonmetallic cable. Metal boxes can be ganged together in various combinations. They are strong and durable, but cost two to three times more than plastic.

Plastic boxes are common in new construction because they are less expensive. They also speed up the rough in because in some cases they do not have to be grounded and can be used without cable clamps if the cables entering them are properly supported outside the box. However, they can't be used with conduit.

Boxes for use with recessed lighting fixtures are usually a part of the fixture assembly. There are two reasons for this arrangement. First, it provides secure mounting for the box in a location that permits access to the wiring when the fixture is removed from its mounting frame. Second, because the box isn't in physical contact with the fixture, except for the high- temperature wiring between them, the house wiring isn't subjected to the heat generated by the fixture. This is an important safety feature.

38 Extending a Circuit: Extended circuit; circuit (incoming power)

39 Installing Boxes: To accommodate thickness of wallcoverings, boxes must extend beyond studs; Octagonal junction box; Ganged Boxes; Square junction box; Box on offset bar; Metal Boxes; Removable sides allow ganging of metal boxes; Metal Ceiling Boxes; Plastic Boxes; Metal flange box nailed to joist

Number of Conductors Permitted in a Box

The NEC strictly governs the number of wires permitted in a box in order to prevent overcrowding. The number of conductors allowed is determined by two things: the size or volume of the box and the size of the wire. This table lists the number of No. 14 and No. 12 wires that can be installed in some of the most commonly used sizes of plastic boxes. The table assumes the box has grounding wires and internal cable clamps. It also assumes the one-gang boxes contain one strap-mounted device, the two-gang contain two devices, etc. You can add one wire if there aren’t cable clamps in the one-gang boxes only.

13.5 cu. in. 1-g switch box

16 cu. in. 1-g switch box

18 cu. in. 1-g switch box

32.5 cu. in. 2-g switch box

46 cu. in. 3-g switch box

60 cu. in. 4 switch box

22.5 cu. in. ceiling box (no device)

36.6 cu. in. 1-g square box

39.1 cu. in. 2-g square box

2-#14 or 2-#12

4-#14 or 3-#12

5-#14 or 4-#12

10-#14or 8-#12

15 - #14 or 12 - #12

20 - #14 or 16 - #12

9 - #14or 8-#12

14 - #14 or 12 - #12

13 - #14 or 11 - #12

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Mapping Your Existing Circuits

Before planning a major remodeling job or addition, you should get acquainted with your existing electrical service. In other words, know what you have to work with. If there is no floor plan that documents the electrical layout of the house, this is a good time to make one. It is one of the most useful documents you can have in your home- management file.

First, go to the service panel and label every circuit breaker or fuse with a number if they aren't already labeled. Next, draw the floor plan of the house. This drawing doesn’t need to be meticulous or to precise scale but it should be legible, and there should be a separate sketch for each floor, including the basement and at tic. Now, using the electrical symbols shown, plot the approximate location of all the switches, receptacles, and permanent lighting outlets on each floor, and then draw dashed lines between the switches and the receptacles and light fixtures they control.

Also draw in the outlets for the 240-volt and 120-volt individual branch circuits and the 120-volt small-appliance circuits. Now begin tracing the circuits in the house.

Choose a time when the house is quiet. Plug a radio into a receptacle and turn it on. Go to the panel and flip breakers off and on, or unscrew fuses, until the radio goes off. Mark that receptacle on the drawing with the corresponding circuit number. Return to the radio, move it to another receptacle, and repeat the process.

This won’t be as time- consuming as you might think because you soon will notice patterns emerging, and you will be able to guess with a fair degree of accuracy the circuit to which the next receptacle is connected. You may find, for example, that all the lighting receptacles are on separate circuits, although it's more likely they will be on one of the general circuits in the room in which the lighting is installed. If you have someone to work with you, moving the radio while you flip breakers and record circuit numbers, the job will go quickly.

Once you have traced the general-purpose branch circuits, go to the kitchen area and trace all the small- appliance circuits using the radio as your guide. Identify the 120-volt individual branch circuits by tripping the remaining circuit breakers, one at a time, and checking the dish washer, food disposer, and so forth, to see if they run. Label these receptacles with the appropriate circuit number. Use this same method to identify the 240-volt individual branch circuits as well.

Once completed, this drawing can be used to determine at a glance which outlets are on which circuits. It also reflects the branch-circuit loading throughout the house. You certainly don’t want to extend a branch circuit that's already heavily loaded. It’s also helpful to know in advance everything that's going to be turned off when a given circuit breaker is opened.

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