Avoiding Electrical Hazards
In the 1990's AASHTO recognized a hazard with the current wiring methods of the time. Those conventional wiring methods, still used today, were identified to pose a potential deadly threat by the electric circuits that are exposed after impact by an errant vehicle. There are documented cases of motorists who survived the impact with a luminaire pole, only to be subsequently killed from the resulting explosion, fire, or electrocuted from exposed conductors on, near or under a vehicle. The explosion and fire are usually caused when the fuel tank ruptures, the vehicle having been caught on an improperly constructed foundation, and the electrical system sparks repeatedly until the fuel explodes. In other incidences, medical personnel have been delayed from attending to victims because of the risk of electrical shock from exposed conductors near or under a vehicle (Highway Engineering Handbook, 2 ed.).
Although AASHTO had set standards for breakaway poles and foundations, it was also realized that the pole wiring system must also be capable of properly separating (AASHTO Standard Specification for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, 4th ed. (2001). One reason is that the tensile strength and wire size of conventional systems directly affects the trajectory of the falling pole. Another reason is that improper separation of the electrical cabling can result in bare conductors that are still energized, posing an electrical and possible fire hazard at the accident site.
Prior experiences show "Breakaway fuse holders", which have been used as an alternate to an AASHTO compliant PCDS, frequently perform improperly during an accident situation. Rather than properly separating, the device frequently pulls off the wire, leaving an exposed end that is potentially deadly. These widely used "breakaway fuse holders" have not been certified by testing, nor do the systems they are installed in meet the latest AASHTO standards (see figure 1).
The MG²/Duraline PCDS (DOTPLUG®) is a great example of a current product that meets current AASHTO standards and avoids the hazards mentioned above (see figure 2). Avoiding these hazards also greatly reduces the liability of the DOT, Utility Companies, design engineers, and others in relation to the electrical wiring system. Another benefit from the use of this type system is the reduction of maintenance/repair cost and time. Further advances like the incorporation of a "ground fault circuit interrupter" (GFCI/ELCI) into the wiring systems is helping avoid fatal and costly accidents resulting from worn or poorly maintained Municipal lighting systems (see electrical injury/death media). It is essential that as a DOT, Municipality, Utility Compnay or as a electrical engineer; that they be educated to avoid these hazards and to abide by all current AASHTO and/or Electrical Standards.
PCDS - Thwarts Copper Thieves Targeting Highway Lighting Systems
In our Media section, you can browse to see that Thieves across the Nation and Canada are targeting Interstate/Highway lighting systems. They are after the valuable copper which is fetching over $3 a pound at recycling facilities. The Hawaii DOT has spent about $300,000 to replace wiring stolen from overhead lights, and experts say that figure could top $1 million once the wiring is replaced. This problem is not isolated to any specific region. Reports range from San Francisco, California to Charlotte, North Carolina. According to California Highway Patrol Officer Jennifer Hink, she says freeway wire theft is occurring an average of once a week. She says those stranded in conked out vehicles at night are facing dangers in Los Angeles, Orange and Riverside counties.
Thieves will simply pull a vehicle up to a lighting pole and tie off the #4 or #6 copper to a trailer hitch and take off, stripping the pole and pulling hundreds of feet of copper from the ground. Besides costing the tax payers millions of dollars in stolen copper, these thieves are leaving drivers in the dark. So how can a PCDS stop thieves wanting the copper and save valuable tax dollars in replacing wire?
The Design of a PCDS like the MG² DOTPLUG® is modular. There are three main components: a luminaire cable to the fixture, a fused plug that runs to the base of the pole, and a distribution block. Thieves tying off to the luminaire cable will find a 14-3 SOWA cord. Thieves tying off to the cord in the base of the pole won't get too far trying to pull the molded fused plug through a narrow conduit. At worst, the 6 to 11 ft piece of SOWA cord that feeds the pole base would either be ripped, or unplugged. What they end up at best with is 14-3 SOWA cord that went to the fixture and possibly a 6 to 11 foot piece of cord that went to the distribution block. The valuable #4 or #6 is left untouched in a protected junction box. In this scenario, the design of the MG² PCDS would keep other lights on the system burning. Plus each of the "plug-in" type components of the MG² PCDS is easily replaceable. This dramatically reduces replacement and repair cost and time to the lighting system.
Electrical Hazards/Copper Theft - Solutions
Figure 1 -Click Image to Englarge
Figure 2 -Click Image to Englarge
Figure 3: Breakaway fuse holders are ripped off during an accident situation. Click Image to enlarge
Figure 4: Example of a pole knockdown using an AASHTO Compliant PCDS.
Click Image to enlarge