BACK-WIRING POSES FIRE HAZARD
BY RONALD J. RAKOSNIK
At 11:51 hours on Friday, January 21, 1994, the Lombard (IL) Fire Department 911 dispatcher received a call reporting heavy smoke on the eighth floor of a 12-story high-rise apartment building. The box alarm brought in four engines, two truck companies, a heavy rescue squad, an advanced life support (ALS) unit, and two chief officers.
Engine 43, the first company on the scene, reported nothing visible from the outside of the building. When the engine company arrived on the reported fire floor, it encountered heavy smoke conditions on the south end. During the size-up, it was determined that there was a fire in apartment #812. Forcing entry into the apartment, firefighters found the fire in a back bedroom. It was extinguished within a few minutes. Although not large in size, the fire created extensive amounts of smoke because of the quantity of plastics and vinyls in the apartment.
THE INVESTIGATION
Whenever the first-arriving officer reports a working fire, the Lombard Fire Investigation Unit (FIU), of which I am a member, is automatically requested to determine origin and cause. In the suspected area of the fire`s origin, a V-pattern was evident and pointed in the direction of the electrical outlet. In a later interview with the tenant of the fire apartment, he reported that the only item plugged into the outlet was an oil-filled space heater, which was five feet long and approximately eight inches high.
The space heater was positioned near a sliding glass door that had a western exposure. During this particular time, the Chicago area was experiencing temperatures reaching highs of -10°F to -20°F. The tenant said the space heater had been set on the highest setting for the previous seven days and seven nights. The FIU, on completion of the preliminary investigation, believed that the space heater was not the cause of the fire but a contributing factor to it. The FIU determined the area near the outlet to be the point of the fire`s origin. On further questioning, the tenant confirmed, “The only thing plugged into the outlet was a space heater.”
The failure, the result of a poor connection, occurred at a point where the branch circuit wire attached to the receptacle. When the heater was operating in the receptacle, it was drawing its rated current, 11.8 amperes, a current level well below the rating of the circuit breaker (15 amperes). The circuit breaker did not operate in this case because a breaker intervenes only when it senses a current level greater than the rating. In this instance, the current never exceeded the 11.8 amperes the heater would draw. As a result, the circuit breaker, for all practical purposes, was oblivious to the fact that the connection point was failing. This would be the case no matter where the failing connection was occurring. Neither a fuse nor a circuit breaker is designed to detect this type of failure.
The space heater, the electrical cord (what was left of it), the electrical outlet, the electrical box, all electrical wiring from the box, and the breaker from the electrical panel were removed for close examination. All the evidence was sent to Richard Kragh of Kragh Engineering, Inc., an electrical engineering firm in North Aurora, Illinois. Kragh specializes in fires thought to be caused by electricity. He analyzed the space heater and confirmed that the switch on the space heater had been in the high setting at the time of the fire. After close examination of the space heater, it was determined that the heater itself did not malfunction and cause the fire, but it placed an extreme draw on the electrical outlet for an extended period of time.
BACK-WIRING
The next object examined was the electrical outlet itself, which was connected by a practice commonly referred to as “back-wiring.” When a wire is back-wired to an outlet, the ends of the conductors are stripped of insulation for about one-quarter inch. There are four holes in the back of the receptacle–to accommodate two hot and two neutral wires–in which the stripped wire ends are inserted. Internal to the receptacle are metal tabs that “bite” into the bare wire end. The tabs are connected to the appropriate female portion of the receptacle. They are set at a slight angle so that once they “bite” into the wire, any pulling on the wire will make them dig into the wire.
A more familiar method of wiring a receptacle is using the screw terminals. Here, the wire is also stripped. The difference between the two wiring methods is the amount of contact surface between the portion of the receptacle making contact and the wire. Generally, back-wiring has a greater tendency to result in a “poor” or high-resistance connection. When the connection fails, heat is produced. The mechanism is resistance heating or I2R heating, where “I” is the current flowing through the connections and “R” is the resistance of the connection. All connections have resistance, so all connections will heat to some degree. When the connection becomes sufficiently poor, the resistance will increase to a point where the heating will become significant.
The Lombard FIU determined that the space heater would draw 11.8 amperes at the high setting it had been on at the time of the fire. Since the termination to the receptacle was poor, sufficient heat was generated to cause adjacent combustibles to ignite. Once they were ignited, the fire spread to the room.
We believe the back-wired outlet heated up at the connection and consequently was unable to carry the load of electricity the space heater demanded. The outlet got hot, igniting combustibles in the area of the outlet and eventually in the room.
CODES AND BACK-WIRED RECEPTACLES
Back-wired receptacles are accepted by the National Electric Code® and are recognized by Underwriters Laboratories. Back-wiring is an inexpensive and fast way to wire a receptacle or switch. If properly installed, back-wired receptacles may perform as well as any other device. However, there appears to be a tendency not to install these devices properly.
On February 10, 1994, I advised James Bandel, Village of Lombard building inspection supervisor, of the findings involving the apartment fire. Currently, our building code does not permit back-wiring of outlets unless it is the “end of a run outlet.” The receptacle involved in the fire was an “end of a run outlet.”
On April 12, 1994, Deputy Chief Tonne (chief of operations) and I attended the Village of Lombard`s Electrical Commission meeting to express our concerns and ask that the back-wiring of outlets be eliminated from our code. After some discussion, the Electrical Commission voted 6 to 1 to prohibit the back-wiring of outlets in new construction in the village.
As in the past whenever the FIU found a building construction problem, product failure, or other practice that was potentially hazardous to our citizens, the matter was brought to their attention. In this case involving back-wired receptacles, we felt it necessary to make as many people as possible aware of their potential danger. n
RONALD J. RAKOSNIK, a firefighter/paramedic with the Lombard (IL) Fire Department, has been a member of its Fire Investigation Unit (FIU) for nine years. He is an Illinois state-Certified Fire Investigator and member of the International Association of Arson Investigators. A Certified Fire Officer I and II, Rakosnik has an associate`s degree in fire science and attended the National Fire Academy in Emmitsburg, Maryland (Cause and Origin); the Federal Law Enforcement Training Center in Glynco, Georgia (Advanced Arson for Profit); and numerous seminars pertaining to the fire investigation field.
