The Phantom Menace: Electrical Power and Classroom Technology

By Will Craig
Multimedia Systems Consultant
Elert & Associates

Overhead transparency projectors are not picky about electrical power. The same cannot be said about current digital projection technologies, sound reinforcement equipment, integrated control systems, codecs, and streaming servers. Losses to the U.S. economy from electrical power quality issues are estimated to be in the $15-$25 billion range. Even these numbers don’t include the whole story for educational institutions: intermittent problems, projector lamps being replaced too frequently, and equipment burning out long before it should.

A recent visit to a 1-year-old smart classroom installation at a Midwestern university highlighted the importance of electrical power issues. The facility was not on the main campus, and was out on the periphery of a metropolitan area. A large dividable auditorium (with seating for several hundred) was equipped with two ceiling-mounted projectors. Conduits ran from floor boxes in the front of each half of the front room to a control room in the back, and then to the projectors. Because of the distances involved, and the desire to simplify the connectivity issues involved in mobile podiums and floor boxes in a multi-purpose space, UTP (unshielded twisted pair; CAT-5/6) connectivity for audio, video, and control was designed.

The normal problems were identified and fixed during the shake-out period shortly after completion. There were several cases of defective equipment, faulty terminations, etc. Soon a new problem emerged. One of the projectors would suddenly freeze up in a mode that could not be accessed through the normal menu commands. Worst of all: it would do this right in the middle of a presentation or a class. To unfreeze the projector, the unit had to be manually unplugged and reconnected – a difficult proposition for the instructor when the projector is 18 feet in the air! Various troubleshooting was done by the vendor, including swapping the two projectors to see whether the problem moved with the projector. It did not. Both projectors were susceptible to the problem, but one more so than the other. No matter how many trips the vendor made to assess, troubleshoot, or correct the problem, there was no apparent solution.

A meeting was called with the university, the architect, the general contractor, the AV vendor, and the AV consultant all in attendance. Several interesting details were shared at the meeting:

A generator had been installed as part of the building project. This was no ordinary emergency generator, however. As part of the recent trend toward “distributed generation,” this generator is available to the local power utility to provide power, not only to the university facility, but also to the local grid. This brings in revenue for the university when in use. The generator had been turned on and off up to 15 times per day during the periods of greatest projector trouble.

The measured electrical voltage to the equipment rack varied by as much as 25 volts during a two-month period while a multi-meter was recording. The rack had voltage regulating equipment installed, but the projectors (on the same circuit) did not.

The floor boxes from which the UTP cables ran to the AV rack were rusty. Further investigation and removal of the UTP cabling found that the conduits underneath the slab-on-grade construction were filled with water. New AV UTP cabling was reinstalled to wall plates on the front wall.

After the UTP cabling was relocated to the wall plates, the intermittent problem has not recurred for two months and counting.

For good measure, a voltage regulation device was mounted above each projector (to the mounting pipe) to maintain constant voltage to each projector.

While it is not certain that the problem has been fully addressed, here are some smart classroom electrical power lessons I would pass along from this and other projects.

Lesson One: Use an extension cord when troubleshooting AV systems. Many projection image problems disappear when the source (document camera, PC, etc.) is connected to the same outlet as the projector. This can quickly place responsibility where it needs to go (AV consultant/contractor vs. electrical engineer/contractor) to get a vexing problem fixed quickly.

Lesson Two: Check to see what kind of electrical loads are on the same electrical service as your smart classroom equipment. Typically, 80% of power quality issues are generated within the building you are working in, so check whether intermittent problems are concurrent with other activities (generator start/stop, HVAC, large motors, etc.).

Lesson Three: UPS (Uninterruptible Power Supply) is not the solution for every problem. While it can provide a smooth supply of power to sensitive devices such as projectors, the size, cost, and battery replacement issues can make installing them everywhere prohibitive. Voltage regulators, such as those from APC and Furman, are much smaller, less expensive, and do not require the same degree of maintenance as do a UPS. For less than $100, a voltage regulator can be a cost-effective way to potentially extend projector- and lamp-life in difficult electrical environments.

Lesson Four: Make your needs clear to your electrical engineer and/or electrical contractor for building and renovation projects. Ground loops, differences in ground potential, and unbalanced power can be the bane of any high-tech teaching facility with networked classrooms.

Will Craig CTS-D, CSI is a multimedia systems consultant with Elert & Associates, a nationwide technology consulting firm specializing in working with higher education and K-12 clients.

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