The most recently available statistics from the National Fire Protection Association, for the years
1993 – 1997, indicate 41,200 home structure fires per year were caused by ‘electrical
distribution.’ These electrical distribution fires took the lives of 336 civilians, caused 1446
civilian injuries, and cost $643.9 million in property damage each year. These figures include
fires with other equipment involved in ignition, but do not include power cords or plugs which
are part of specific appliances. These 41,200 fires account for 9.7% of total home structure
fires during the period. Electrical distribution causes place 5th out of the 12 major causes. The
$643.9 million in property damage represents 14.4% of the total fire damages, making electrical
distribution ignition the second leading cause (behind arson or suspicious causes). Statistics
compiled earlier, for 1985 – 1994, by FEMA show very similar results: electrical distribution
equipment was the fifth-largest cause of fires, the fourth most significant cause of fire fatalities,
and the second-ranked cause of property loss.  Electrical distribution equipment causes are listed
in Table 1.
Table 1 - Leading Causes of Electrical Fires
Cause of Fire
Percent of Total
Fixed Wiring
Cords and Plugs
Light Fixtures
Switches, Receptacles and Outlets
Lamps and Light Bulbs
Fuses and Circuit Breakers
Meters and Meter Boxes
Unclassified or Unknown Distribution Equipment
Electrical arcing as a fire cause

One one of the major causes of electrical fire ignition is arcing. Arcing is when the
electrical current bridges a gap, often an air gap, and jumps to an adjacent conductor.
There are two kinds of arcs, a PARALLEL arc, and a SERIES arc. Each type occurs
differently, but both types cause elevated temperatures of wires, connectors, insulating
materials, etc. Both types can lead to a fire.

Parallel Arcing

Parallel arcs occur when the current bridges a gap between a hot conductor and a
neutral. A second type of parallel arc is when the hot conductor arcs to the safety
ground, a metal conduit or junction box, or other electrically grounded object. These
types of arcs
may trip a conventional circuit breaker. A special class of circuit breaker
called an
arc fault interrupter has been made available to specifically protect against
parallel arcing. A third type of circuit breaker, called a
ground fault interrupter is also
available. This type of protective device is intended to prevent electrocution by detecting
stray current paths (such as through a person's body) to ground, and cut off the power
before injury occurs. Since they detect stray current to ground (that which does not
return through the neutral wire as it should), they can also detect a parallel arc when it
occurs to a ground wire or other electrically-grounded object.

Series Arcing

Series arcing, on the other hand, occurs in series with the current flow. A series arc can
occur anywhere along either the hot or the neutral wire, but it most often occurs where
connections are made. Typical locations include inside a distribution panel, meter box or
socket, or at any of the numerous electrical junction boxes, outlets or switches that are
present in a structure. Most often, series arcing is caused by loose electrical connections,
where the mechanical interface is not tight, or has loosened with age, temperature
cycling, faulty installation, damage, etc.

One would initially think that a series arc will only occur briefly, and then the conductors
will separate enough that the current no longer flows, drawing the attention of the
building occupants to the problem. Sometimes, these series arcs show up as an
intermittent connection, that makes and breaks, causing lights to flicker or electrical
equipment to sporadically fail. Occasionally this is observed by the occupants, and a
remedy is sought. But other times, a much more insidious occurrence takes place, one
that the occupants of a home or business are seldom aware of.

The Glowing Connection

The glowing connection usually begins its life as an intermittent connection, or a series
arc. But then something very strange happens. The localized heating caused by the series
arc makes the connected metals begin to oxidize. Once the contact points are oxidized,
electrical resistance begins to increase. This increase in resistance, because it is
in series
with the normal current flow, causes resistance heating just like in an electric heater. The
heating that occurs is very localized, but it begins to cause an alloying of the dissimilar
metals. These alloys have additional, and unexpected, electrical properties. That is, they
semiconductors, and behave in a non-linear fashion to electric current flow. Because
of this non-linear behavior, heating can occur at very low currents such as those drawn
by a "wall wart" type battery charger or AC adapter. A glowing connection may take
hours, days or years to develop but once it has any flickering of lights or intermittent
behavior of electrical devices ceases. Instead, a very low voltage drop occurs (usually 2
volts or so), even when relatively high current electrical loads are in use. Because of this
small voltage drop, incorrect behavior of the load seldom occurs, and so it does not
attract the attention of the user or building occupant.

Circuit breakers are useless

Common household circuit breakers are unable to protect against this kind of electrical
failure. Because the fault is in series with normal current flow, the current does not
increase, and the circuit breaker cannot detect it and open. Ground Fault Interrupters are
also incapable of detecting a glowing connection, because there is no current flow to
ground. Even Arc Fault Interrupters will not detect a glowing connection, because there
is no short-circuit and resulting high current, like with a parallel arc.

A conventional circuit breaker or an Arc Fault Interrupter may open if the heat damages
the wiring insulation enough to cause the hot and neutral leads to short. A Ground Fault
Interrupter may open if the heat damage results in a short from a hot wire to the ground
wire, or to a grounded metal object. However, long before this level of damage occurs,
the combustibles that are present (insulation, plastic outlet or switch housing, etc.) can
easily ignite.

Older homes and buildings

Older buildings are more prone to glowing connections because of the age of their
electrical distribution and wiring components. Age, temperature cycling, vibration,
moisture, all have an effect on the integrity of an electrical connection. Buildings and
homes older than even a few years are possible candidates. Copper (or aluminum) wire is
soft, and it crushes under the tightening force of the retaining screws. Once the copper
"takes a fit", a loose connection can easily result. Vibration and hot/cool cycling can
further loosen the screw. Repeatedly connecting and disconnecting plugs from a wall
outlet can wear out the contact leaves inside, making the plug very loose. And the mere
action of plugging and unplugging causes movement that aggrivates loose connections.
Newer "back wired" outlets have no screws - they depend on a spring-loaded contact
that touches the bare wire inserted at the back. These outlets are also prone to developing
a glowing connection. Research conducted in the 1960s shows that brass and copper
make an ideal cocktail from which a glowing connection may emerge. Brass is widely
used as a contact material in electrical distribution systems.

Fire in the walls

If ignition occurs inside a junction box, or at a receptacle or wall switch, fire will spread
to wooden structural members inside the walls, and continue to spread fire and smoke to
other areas of the building. Concealed within the wall void, heat and smoke are delayed in
coming into contact with smoke or heat detectors. The result is a fast-spreading fire,
developing without the occupants' knowledge. By the time the fire is discovered, valuable
escape time is lost, the structure is often fully involved and a total loss by the time the fire
department arrives.

What can be done?

The only way to prevent fires caused by glowing connections is to detect them before
they develop to the point where ignition is imminent. One inventor has developed a small
thermal switch device that is plugged in between an outlet and an electrically-powered
product. One of these would have to be placed at every outlet that has something plugged
into it. This device relies on the thermal conduction of the metal prongs of the plug in the
outlet to trip it off. It would be unable to detect a glowing connection at a wall switch or
junction box in the attic. The only way to detect and protect against this hidden danger is
to be able to detect the unique electrical characteristics of a glowing connection.

The Solution

The best way to find these latent fire causes is to observe the special signatures of
voltage, current and resistance which they exhibit. An electrical test unit, operated by a
home inspector prior to closing on the sale of a used home or other structure is an
excellent way to give the new owners peace of mind. Also, electricians would be able to
offer the testing to existing tennants as an on-demand service. Similar to cleaning and
inspecting the chimney, cleaning the clothes dryer duct, and checking fuel-burning
appliances for correct operation, testing a building for glowing connections will go a long
way toward saving lives and reducing property damage.