Info

Furnace, forced-air gas

6.5 to 13

780 to 1560

Water heater

15.8 to 21 (240-v)

3800 to 5040

Knockouts

Metal brace clamp

Grounding wires

Grounding .screw

Coverplate

NM (nonmetallic) cable

Wire connector

Octagonal boxes usually contain wire connections for ceiling fixtures Cables are inserted into the box through knockout openings and are held with cable clamps Because the ceiling fixture attaches directly to the box the box should be anchored firmly to a framing member Often, it is nailed directly to a ceil ing joist However metal braces are available that allow a box to be mounted between |oists or studs A properly installed octagonal box can support a ceiling fixture weighing up to 35 pounds Any box must be covered with a tightly fitting coverpiate and the box must not have open knockouts

Electrical Boxes

The National Electrical Code requires that wire connections or cable splices be contained inside an approved metal or plastic box. This shields framing members and other flammable materials from electrical sparks. If you have exposed wire connections or cable splices, protect your home by installing electrical boxes

Electrical boxes come in several shapes. Rectangular and square boxes are used for switches and receptacles Rectangular (2" x 3") boxes are used for single switches or duplex receptacles Square (4" x 4") boxes are used anytime it is convenient for two switches or receptacles to be wired or "ganged" in one box. an arrangement common in kitchens or entry hallways. Octagonal electrical boxes contain wire connections for ceiling fixtures

All electrical boxes are available in different depths A box must be deep enough so a switch or receptacle can be removed or installed easily without crimping and damaging the circuit wires Replace an undersized box with a larger box. using the Electrical Box Chart (right) as a guide The NEC also says that all electrical boxes must remain accessible Never cover an electrical box with drywall. paneling, or wallcoverings

See Inspector's Notebook:

• Electrical Box Inspection (pages 128 to 129).

• Common Cable Problems (pages 124 to 125).

Electrical Box Chart

Box shape

Maximum number of individual wires in box*

14-gauge

12-gauge

2' x 3'

2'A' deep

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