Above Ground Wiring Installation

NM, UF, AC, and MC Cable Installation
1. Use NM, UF, AC, and MC cable where the cable is not subject to physical damage. Physical damage can occur unless the cable is covered by drywall or by other material or unless the cable is run in conduit or tubing. Physical damage includes damage by sunlight. Read the full Topic

Below Ground Wiring Installation

Below Ground Wiring Burial Depth
1. The following table lists how much cover is required for wiring and conduit buried underground. Depths are in inches.

Protection where Wires Emerge from Ground
1. Protect wires where they emerge from the ground using enclosures or raceways beginning at the wire’s minimum burial depth or at least (≥) 18 inches below where the wires emerge from the ground, whichever is less. Extend the protection to at least (≥) 8 feet above fi nished grade.
2. Protect wires at the point where they enter the building. Read the full Topic

Knob and Tube Wiring

Knob-and-tube wiring is found in some older homes built before about 1940. It consists of two separate wires supported on insulators (knobs) and running through insulating cylinders (tubes) when the wires pass through framing. You may tap into and extend existing knob-and-tube wiring if you use a currently approved wiring method (such as NM cable) for the extension and if you enclose the tap in an approved junction box.

Knob-and-tube wiring is often part of an obsolete and undersized electrical system that is easy to overload. Carefully calculate the existing and new load on the existing knob-and-tube circuit and do not overload the existing circuit. Do not use existing knob-and-tube wiring if the insulation is deteriorated. Do not place insulation around or over knob-and-tube wires. Insulation can allow the wires to overheat and cause a fire.

While extending existing knob-and-tube wiring is not prohibited, it is not recommended. It is usually wise to upgrade to a modern electrical system rather than extend an obsolete and potentially dangerous existing knob-and-tube system.

Wiring Methods and Allowed Uses

Wiring Methods Currently Allowed
1. The following table lists the wiring methods currently allowed in residential construction. Note that certain wiring methods may not be used in certain applications.

Circuit Wires in Same Raceway
1. Run all wires for the same circuit, including grounding wires, in the same cable, raceway, or trench. This includes service, feeder, and branch circuit wires.
2. You may not run equipment grounding wires (e. g., for a receptacle or switch) to a water pipe, as is done in some older homes. This att empt at grounding violates this provision and grounding electrode provisions. Read the full Topic