Bob Dolph Answers Questions on PLC, Testing CCTV Cabling

Q: I just put a basic Power Line Carrier (PLC) residential lighting automation system in for an alarm customer of mine. Some of the devices work and some don’t. What could be causing the problem?
A: A typical 220 VAC circuit in a house is broken up into two 110 VAC circuits for all the home’s devices. There is a good chance that the signal going over the power lines is not getting from the one 110VAC circuit to the other one. You will need to install a coupling device to pass the PLC signal between the two circuits. One way is to wire a coupling device between the two circuit breakers. However, many low voltage installer do not have an electrical license so you may want to look at a plug-in coupler that can plug into a 220 VAC device such as an electric dryer or stove.

Q: I would like to have my techs be able to test video cabling and connectors. Any tips I can do with existing equipment to be able to test CCTV cabling?
A: Sure, one suggestion is to simply place a 75 ohm load (inexpensive BNC types are easily available; you should have at least one in your toolbox) on one end of the cable and then test with a digital multi-meter (DMM) on the to other end. You should see the 75 ohm resistance reading. Test from shield to center conductor. This is a quick and easy test to see if there are any possible shorts, opens, termination errors, or even a miss-labeled cable.


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