by Nick Gromicko, Rob London and Kenton Shepard

 

Armored cable (AC), also known as BX, was developed in the early 1900s by Edwin Greenfield. It was first called “BX” to abbreviate “product B – Experimental,” although AC is far more commonly used today. Like Romex cables, they cannot be used in residences higher than three stories, and the rules for protection and support of AC wiring are essentially the same as the rules for Romex. Unlike Romex, however, AC wiring has a flexible metallic sheathing that allows for extra protection. Some major manufacturers of armored cable are General Cable, AFC Cable Systems, and United Copper Systems.

 

 

These cables begin at the splice and enter the meter. They are not permitted inside homes, with the exception of “style R” SE cable that can serve as interior wiring in branch circuits for ovens and clothes dryers. Style R cables should be clearly marked on their jacket surfaces.

 

 

Most houses constructed prior to World War II were wired using the knob-and-tube method, a system that is now obsolete. They are more difficult to improve than modern wiring systems and are a fire hazard. Knob-and-tube wiring is supported with ceramic knobs, and runs intermittently though ceramic tubes beneath framing and at locations where the wires intersect. Whenever an inspector encounters knob-and-tube wiring, s/he should identify it as a defect and recommend that a qualified electrician evaluate the system. The following are a few reasons why inspectors should be wary of this old wiring system:

In summary, inspectors should understand the different types of conductors that are commonly found in homes. 

 

 

 

Situations in which arcs may be created:

• electrical cords damaged by vacuum cleaners or trapped beneath furniture or doors.
• damage to wire insulation from nails or screws driven through walls.
• appliance cords damaged by heat, natural aging, kinking, impact or over-extension.
• spillage of liquid.
• loose connections in outlets, switches and light fixtures.

E3802.12 Arc-Fault Protection of Bedroom Outlets. All branch circuits that supply120-volt, single-phase, 15- and 20-amp outlets installed in bedrooms shall be protected by a combination-type or branch/feeder-type arc-fault circuit interrupter installed to provide protection of the entire branch circuit.

Exception: The location of the arc-fault circuit interrupter shall be permitted to be at other than the origination of the branch circuit, provided that:

1. The arc-fault circuit interrupter is installed within 6 feet of the branch circuit overcurrent device as measured along the branch circuit conductors, and
2. The circuit conductors between the branch circuit overcurrent device and the arc-fault circuit interrupter are installed in a metal raceway or a cable with metallic sheath.

• Branch/feeder—installed at the main electrical panel or sub-panel.
• Outlet circuit—installed in a branch-circuit outlet.
• Combination—complies with the requirements of both the branch/feeder and the outlet circuit AFCIs.
• Cord—a plug-in device connected to the receptacle outlet.

Nuisance Tripping

• Check that the load power wire, panel neutral wire and load neutral wire are properly connected.
• Check wiring to ensure that there are no shared neutral connections.
• Check the junction box and fixture connections to ensure that the neutral conductor contacts a grounded conductor.

• Never use anything but the proper fuse to protect a circuit.
• Find and correct overloaded circuits. 
• Never place extension cords under rugs. 
• Outlets near water should be GFCI-type outlets. 
• Don't allow trees near power lines to be climbed. 
• Keep ladders, kites, equipment and anything else away from overhead power lines. 

 

 

MORE SAFETY PRECAUTIONS :

Rod and pipe electrodes not less than 8 feet (2438 mm) in length and consisting of the following materials shall be considered as a grounding electrode:

1. Electrodes of pipe or conduit shall be not smaller than trade size ¾ (metric designator 21) and, where of iron or steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.
2. Electrodes of rods of iron or steel shall be at least 5/8 inch (15.9 mm) in diameter. Stainless steel rods less than 5/8 inch (15.9mm) in diameter, nonferrous rods or their equivalent shall be listed and shall be not less than 1⁄2 inch (12.7mm) in diameter.

Notes

• Although the 2006 IRC does not mention whether the rod may be driven at an angle, the 1998 California Electrical Code allows for a maximum oblique angle of 45 degrees from the vertical.
• An electrician can install two grounding rods if necessary. They should be at least 6 feet apart from one another.
• In Canada, grounding rods should be 10 feet long and two are required. 

Concrete-Encased Electrodes (Ufer Grounds)

 

This electrical grounding technique was invented during World War II in Arizona, and is commonly called “Ufer” after its creator, Herbert G. Ufer. The United States Army was concerned that lightning or static electricity could cause the accidental detonation of explosives that were stored in igloo-shaped vaults. The desert climate restricted the usefulness of grounding rods, which would have to be driven hundreds of feet into the dry earth in order to be effective. Ufer advised the military to connect ground wires into the concrete-encased steel reinforcement bars (re-bar) of the bomb vaults in order to dissipate electricity effectively into the ground. Testing confirmed his theory that the relatively high conductivity of concrete would allow electric current to dissipate into a large surface area of earth. The Ufer method is more common in newer residential construction and requires a metal frame. It might be difficult for an inspector to detect this type of electrode. The 2006 IRC details Ufer grounds as follows:

 

An electrode encased by at least 2 inches (51 mm) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 20 feet (6096 mm) of one or more bare or zinc-galvanized or three electrically conductive coated steel reinforcing bars or rods of not less than 1/2 inch (12.77 mm) diameter or consisting of at least 20 (6096 mm) feet of bare copper conductor not smaller than 4 AWG shall be considered as a grounding electrode. Reinforcing bars shall be permitted to be bonded together by the usual tie wires or other effective means.

 

Metal Underground Water Pipes

 

A building’s plumbing system can be connected to the ground wire and function as a grounding electrode. For some time, this was the only mandatory grounding electrode type and it was generally preferred over other methods. As of 1987, however, this method became the only one that must be supplemented with another type of electrode. This transition is due to the increased popularity of nonconductive dielectric unions and plastic pipes. When plumbing has been replaced with plastic pipes a notice is required to be placed at the electrical service panel that states that there is a non-metallic water service. Inspectors will not be able to tell if outdoor water pipes that run to street water mains have been replaced with plastic components.

 

Inspectors should check for the following:

• Ground wires should be firmly attached to water pipes close to the point of entry to the building. A ground wire that is loosely tied around a pipe is inadequate.
• Gas pipes should never be used as grounding conductors. They usually are made of plastic at the exterior of the home and carry flammable gases that may ignite if exposed to electrical current.

The 2006 IRC states the following about water pipe electrodes:

 

 

Less Common Grounding Electrodes

 

The previously mentioned grounding electrodes constitute the vast majority of grounding systems that inspectors will encounter. The two electrodes described below are far less common, although they are recognized by the IRC. Inspectors might not be able to verify their presence. The 2006 IRC explains them as follows:

 

Plate Electrodes

 

A plate electrode that exposes no less than 2 square feet (0.186 m2) of surface to exterior soil shall be considered as a grounding electrode. Electrodes of iron or steel plates shall be at least 1⁄4 inch (6.4mm) in thickness. Electrodes of nonferrous metal shall be at least 0.06 inch (1.5mm) in thickness. Plate electrodes shall be installed not less than 30 inches (762 mm) below the surface of the earth.

 

Ground Ring Electrodes

 

A ground ring encircling the building or structure, in direct contact with the earth at a depth below the earth’s surface of not less than 2.5 feet, consisting of at least 20 feet of bare copper conductor not smaller than No. 2 shall be considered as a grounding electrode.

 

In summary, a variety of home service grounding electrodes can be used to safely route unexpected electrical charges away from places that they can cause harm. Inspectors should be aware of how they differ from one another and be prepared to spot defects.

 

Aluminum Wiring

Aluminum possesses certain qualities that, compared with copper, make it an undesirable material as an electrical conductor. These qualities all lead to loose connections, where fire hazards become likely. These qualities are as follows:

• high electrical resistance. Aluminum has a high resistance to electrical current flow, which means that, given the same amperage, aluminum conductors must be of a larger diameter than would be required by copper conductors.
• less ductile. Aluminum will fatigue and break down more readily when subjected to bending and other forms of abuse than copper, which is more ductile. Fatigue will cause the wire to break down internally and wukk increasingly resist electrical current, leading to a buildup of excessive heat.
• galvanic corrosion.  In the presence of moisture, aluminum will undergo galvanic corrosion when it comes into contact with certain dissimilar metals.
• oxidation. Exposure to oxygen in the air causes deterioration to the outer surface of wire. This process is called oxidation. Aluminum wire is more easily oxidized than copper wire, and the compound formed by this process – aluminum oxide – is less conductive than copper oxide. As time passes, oxidation can deteriorate connections and present a fire hazard.  
• greater malleability. Aluminum is soft and malleable, meaning it is highly sensitive to compression. After a screw has been over-tightened on aluminum wiring, for instance, the wire will continue to deform or “flow” even after the tightening has ceased. This deformation will create a loose connection and increase electrical resistance in that location.
• greater thermal expansion and contraction. Even more than copper, aluminum expands and contracts with changes in temperature. Over time, this process will cause connections between the wire and the device to degrade. For this reason, aluminum wires should never be inserted into the “stab,” “bayonet” or “push-in” type terminations found on the back of many light switches and outlets.
• excessive vibration. Electrical current vibrates as it passes through wiring. This vibration is more extreme in aluminum than it is in copper, and, as time passes, it can cause connections to loosen.

Identifying Aluminum Wiring

• Aluminum wires are the color of aluminum and are easily discernable from copper and other metals.
• Since the early 1970s, wiring-device binding terminals for use with aluminum wire have been marked CO/ALR, which stands for “copper/aluminum revised."
• Look for the word "aluminum" on the plastic wire jacket. Where wiring is visible, such as in the attic or electrical panel, inspectors can look for printed or embossed letters on the plastic wire jacket. Aluminum wire may have the word "aluminum," or a specific brand name, such as "Kaiser Aluminum," marked on the wire jacket. Where labels are hard to read, a light can be shined along the length of the wire.
• When was the house built? Homes built or expanded between 1965 and 1973 are more likely to have aluminum wiring than houses built before or after those years.

Options for Correction

Aluminum wiring should be evaluated by a qualified electrician who is experienced in evaluating and correcting aluminum wiring problems. Not all licensed electricians are properly trained to deal with defective aluminum wiring. The following corrective actions may be taken:

• Rewire the home with copper wire. While this is the most effective method, rewiring is expensive and impractical, in most cases.
• Splice the aluminum wire to copper wire at the connections using approved wire nuts (called "pigtailing"). This method is only effective if the connections between the aluminum wires and the copper pigtails are extremely reliable. Pigtailing with some types of connectors, even though they might be presently listed by Underwriters Laboratories for the application, can lead to increasing the hazard. Also, beware that pigtailing will increase the number of connections, all of which must be maintained.
• Replace certain failure-prone types of devices and connections with others that are more compatible with aluminum wire.
• Remove the ignitable materials from the vicinity of the connections.
• All connections should be checked and an anti-oxidant paste applied.
• Copalum crimps can be installed. Although effective, they are expensive (typically around $50 per outlet, switch or light fixture).