Arc-fault circuit interrupters (AFCIs) are special types of electrical receptacles or outlets and circuit breakers designed to detect and respond to potentially dangerous electrical short circuits in electrical wiring. 
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How do they work?
 
AFCIs function by monitoring the electrical circuit and promptly breaking or interrupting the electrical current in that circuit. They also are capable of distinguishing safe or normal arcs, such as those created when a switch is turned on or a plug is pulled from a receptacle, from arcs that can cause fires. An AFCI can detect, recognize, and respond to very small changes in wave pattern.

What is an arc?
 
When an electric current crosses an air gap from an energized component to a grounded component, it produces a glowing plasma discharge known as an arc. An automobile depends on an arc from the spark plug to ignite the fuel in the piston cylinder. Another example is a bolt of lightning.  It is a very large powerful arc that crosses an atmospheric gap from an electrically charged cloud to the ground or another cloud. Just as lightning can cause fires, arcs produced by domestic wiring are capable of producing high levels of heat that can ignite their surroundings and lead to structure fires. Electrical problems are responsible for many structure fires every year.
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According to statistics from U.S. Fire statistics website as of 2013 there were well over one millions house fires per year but the number has steadily been declining. Much of the decline should be attributed to education and the use of safety devices such as AFCIs. 

Where are arcs likely to form?
 
Arcs can form where wires are improperly installed or when insulation becomes damaged. In older homes, wire insulation tends to become brittle as it ages and is  prone to cracking and chipping. Damaged insulation exposes the current-carrying wire to its surroundings, increasing the chances that an arc may occur.
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.

Where are AFCIs required?
 
Guidelines have been written into the National Code requiring the use of AFCIs in certain locations in new construction such as bedrooms. Since enforcement varies from one area to another it is recommended that you consult a licensed electrician for recommendations in your area. 


 
What types of AFCIs are available?
 
AFCIs are available as circuit breakers for installation in the electrical distribution panel. 

 
Nuisance Tripping
 
An AFCI might activate in situations that are not dangerous and create needless power shortages. This can be particularly annoying when an AFCI stalls power to a freezer or refrigerator, allowing its contents to spoil. There are a few procedures an electrical contractor can perform in order to reduce potential “nuisance tripping." 
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Arc Faults vs. Ground Faults
 
It is important to distinguish AFCI devices from Ground Fault Circuit Interrupter (GFCI) devices. GFCIs detect ground faults, which occur when current leaks from a hot (ungrounded) conductor to a grounded object as a result of a short-circuit. This situation can be hazardous when a person unintentionally becomes the current’s path to the ground. GFCIs function by constantly monitoring the current flow between hot and neutral (grounding) conductors, and activate when they sense a difference of 5 milliamps or more. Thus, GFCIs are intended to prevent personal injury due to electric shock, while AFCIs prevent personal injury and property damage due to structure fires.
 
In summary, AFCIs are designed to detect small arcs of electricity before they have a chance to lead to a structure fire. 

Adjustable steel columns, also known as screw jacks and beam jacks, and are hollow steel posts designed to provide structural support. An attached threaded adjustment mechanism is used to adjust the height of the post.
 A few facts about adjustable steel columns:

• They are usually found in basements.
• In some parts of North America, adjustable steel columns are called lally columns, although this term sometimes applies to columns that are concrete-filled and non-adjustable.
• They can be manufactured as multi-part assemblies, sometimes called telescopic steel columns, or as single-piece columns.

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The following are potentially defective conditions:​

• The post is less than 3 inches in diameter. According to the 2012 International Residential Code (IRC), Section R407.3, columns (including adjustable steel columns)..."shall not be less than 3-inch diameter standard pipe." Structural engineers -- not inspectors -- decide whether adjustable steel posts are of adequate size. However most posts are 3 inches with exception of shorter posts.
• The post should be painted and protected from rust.
• The post is not straight. According to some sources, the maximum amount out of plumb should not exceed 1 inch. The post should not be bent or damaged.
• The column should be fastened to the floor or imbedded in concrete. The columns in the picture are not fastened correctly.
• The column is not connected to the beam. The post should be connected to the beam above to provide additional resistance against lateral displacement.
• More than 3 inches of the screw thread are exposed.
• There are cracks in upstairs walls. This condition may indicate a failure of the columns.