Seeing the Light At the End of – and Throughout – the Tunnel
Project Considerations
Designing a lighting system for a tunnel can be challenging. For each project it is important to ascertain the power sources and quantity along with the voltage and amperage requirements. Additional design factors include the length and diameter of the tunnel, foot-candles of illumination required, the light fixtures specified and the hue of the earth being mined. It is remarkable how a tunnel can devour the best-engineered lighting scheme if rock hue and type of material being mined is not taken into consideration. Even when all these design factors are utilized during the design phase, it is inevitable that every project has a “consistency of change” as the job progresses. Because of the many changing variables and unforeseen challenges that consistently arise, it is wise to over-engineer the power and lighting systems to assure the project can proceed on schedule.
It is wise to prepare for the worst of conditions to keep the project on schedule and within budget. Boston’s “Big Dig” tunnel project in the 1990s is a good illustration of the need to plan for the harshest tunnel conditions and unknown variables through over-engineering the power and lighting system. In that instance, plastic light fixture sockets were used, which led to repeated lighting outages due to seawater intrusion. The general contractor came to Connomac to put a light system that would withstand the effects of salt water and keep the project moving forward. Connomac’s fully molded neoprene power feeder system with Conno-Change Connector drops for each light fixture solved the problem.
In some regions of the United States and in other countries, underground natural gasses can provide another layer of challenge for powering and lighting a tunnel-mining project. Sometimes the gaseous conditions are known or predicted and sometimes they are unexpectedly encountered as the mining of the tunnel progresses. If gas is a possibility, the lighting must comply with National Electrical Code (NEC) categories that are:
Class 1/Division 1, which will require conduit and seal offs for all fixtures and connectors. This option is very expensive and rarely used for a temporary installation.
Class 1/Division 2, allows the use of cord and cord connectors, rather than conduit, with explosion-proof connectors.
A critical requirement for Class 1 installations (both Division 1 and 2) is the employment of a hyperventilation system.
Experience Underground
Connomac has furnished light and power cords for many tunnels throughout the United States including Toronto, Chicago, Washington, D.C., New York, Indianapolis, Milwaukee and San Francisco.
In all of these projects, the company works closely with the general and electrical contractors to help them with the specifications for the required temporary light cords which may be custom tailored for 480v-3 phase, 277v-3 circuit or 110v/220v-single phase.
The biggest project the company is currently involved with is the SR 99 highway tunnel in Seattle. While the TBM being used to mine the tunnel is currently the world’s largest, it will still encounter many of the same challenges as smaller tunnel projects – although the immensity of the tunnel itself may put fear and trepidation into the mathematical formulas. The key to meeting the challenges of a tunnel so large is building in the flexibility previously discussed to deal with unforeseen conditions, which requires proactively over-engineering the electrical systems. Specifically, the spacing of the lights in a tunnel of this magnitude must be very carefully engineered.
Looking Ahead
With the increased capabilities and efficiencies of tunnel boring machines and the growing need of critical tunnel infrastructure for transportation, water, sewage and storm water retention in major population centers around the world, we expect tunneling to continue to grow in the United States.
As new and larger population centers around the world continue to demand increased tunnel infrastructure, the tunnel market will continue to grow substantially, especially internationally in Canada, India, Mexico, China and South America.
Another area of potential growth in the tunneling industry is the possible new applications of TBMs in the coal mining industry that could stimulate an expansion of tunneling work.
As more and more existing tunnel infrastructure ages, a part of the tunneling market expected to grow is in maintenance upgrades and renovations to keep older tunnels effectively functioning. In this segment of the tunneling market there is a movement toward using Low Smoke Zero Halogen (LSZH) cable in finished subways as contractors do utility and repair work. LSZH cable has been used previously in the aircraft and railroad industries because it reduces the amount of toxic and corrosive gas emitted during combustion. Connomac has developed a LSZH temporary light cord that is approved by NYC/MTA.
Digging and mining tunnels will always be challenging work requiring innovative engineering, construction and products. It is great to see the “light at the end of the tunnel” but even better to see throughout the entire tunnel.
This article was submitted by Connomac Corp. especially for TBM: Tunnel Business Magazine.
Connomac in the Spotlight
Connomac Corp., located in suburban Chicago, manufactures fully molded electrical connectors and temporary lighting systems. The company’s founder, Greg McDonnell, an electrical contractor specializing in tunnel work, formed Connomac Corp. in 1972 because he saw a need for safe, reliable and rugged light and power cords and connectors designed for unique needs of the tunneling industry. Connomac’s products have lit and powered tunnels throughout the United States, Mexico and Canada for over 40 years.
At the time of the company’s founding, it was common practice in large tunnels to illuminate them by stringing wire through insulated brackets and splicing pigtails for light bulbs. The brightness of the lights was limited to 75-watt bulbs because 100-watt bulbs would explode from one drop of water because of the heat differential between 75-watt and 100-watt bulbs. When Tuff Skin bulbs were introduced the bulbs could be higher wattages. As tunnels became larger in diameter, 100-watt bulbs were not bright enough. Therefore, the development of larger and brighter light fixtures became necessary. Connomac developed a waterproof system of cables, connectors and light cords for the harsh environment found in most tunnel projects.
And thus tunnel lighting has evolved into a full array of professional light cord sets that have been ruggedized for the rough treatment they might receive and which can be tailored to the needs of each tunnel project.
In addition, Connomac manufactures connectors and cords to power temporary light fixtures – plus power connectors for pumps, fans, communications, controls and emergency-stop conveyor systems. All of these products are specifically designed to provide safe and reliable power in the harsh environment found in nearly every tunneling project.
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