Construction Corner is a Q&A column committed to answering reader-submitted questions regarding construction and development. Inquiries may be sent to firstname.lastname@example.org.
Q: I have heard about cameras that use existing 120VAC power lines for their video signal and power. What are the limitations to these cameras? How many can you have at a single site?
—Jerry in El Paso, Texas
A: These cameras are great for locations that are impossible to reach without trenching. However, the technology is not yet perfected. From a technical standpoint, you can use one camera per electrical phase. So, on an average site, you could use two cameras; but realistically, one camera per site is all that is recommended.
I have only seen these cameras in a black-and-white version. Their recording quality is on par with an old analog system. Again, they are great for being able to see that back door or dumpster that isn’t accessible by other means, but they are not an alternative to getting a regular coax video system.
Q: We are adding cameras and a security siren outside our of. ce, running all the components across the roof. My nephew is installing the equipment, and I am concerned about him making holes in the top of my building. What is the proper way to run wiring across the roof and penetrate into the structure?
—Becky in Carlsbad, Calif.
A: The answer to this question is related to the type of roof you have, but I can give you a few guidelines. First, I recommend all wiring go through conduit along the roof to protect it from the elements, animals or the occasional HVAC repairman. When running conduit across the roof, don’t use nails or screws to secure it to the roofing material. Instead, secure 12-inch pieces of 2-by-4 block to the roof with mastic or tar at intervals of about 10 feet, then secure your conduit directly to the blocks. This will prevent leaks from screw or nail holes.
When making your penetration into the building for the wire, use a sleeve with a metal flashing that fits snugly over the conduit. Use a lot of mastic or tar around the flashing. Finally, secure a waterproof box to the top of the sleeve, as this is where all of your roof conduit will terminate.
Tony Gardner is a licensed contractor and installation manager for QuikStor, a provider of self-storage security and software since 1987. For more information, visit www.quikstor.com.