CCTV Trouble-Shooting Basics
The performance of any CCTV system can easily be evaluated by the video quality at the monitor and recording end. Although there are many potential problems that can affect the smooth operation of any CCTV system, the vast majority of common issues relate to either transmission media or power. According to industry data collected by leading manufacturers: 1. 65% of service calls are due to problems with video transmission including cables, connectors and their installation; 2. 27% of service calls are related to power (such as inadequate or excessive voltage, grounding problems) and environmental issues (such as temperature or vibration). 3. 7% of system problems are due to installation errors including improper termination, incorrect equipment set-up and mistakes made by installation personnel. Therefore only about 1% of CCTV system problems are caused by actual equipment failure due to defects in material or workmanship. In this bulletin we look at some of the more common problems associated with cable, power and camera signals.
Quick Reference Power & Video Tables
Video Ground Loop – Trouble-Shooting
Ground Loop is a common problem in CCTV installations, especially in large industrial applications. The problem is easily identified on monitors by the 60 cycle bars which slowly move up the video screen. If the problem is minor these rolling bars may be no more than a nuisance but in severe cases can cause the picture to break up entirely on the monitor. The problem is caused by having more than one ground point in the CCTV system. A CCTV system is normally grounded at the monitor end which is connected directly to the 60 cycle main. A Ground Loop is created when the coaxial cable at the camera end becomes locally grounded for any reason. In 60 cycle power systems local grounds return any unbalanced current flow to ground. However each ground point usually has a different voltage potential depending on how uneven the current flow of the power load is in the building or facility. The voltage differential can be measured by disconnecting the video cables at the monitor end and using a voltmeter to measure between any two shields of the incoming video cables. If you have significant 60 cycle bar problems at the monitor you will find there is a large voltage differential between the video cables.
Resolving Ground Loop Problems
Ground Loop problems can be resolved by making sure that only one end of any video cable is connected to a local ground. Make sure the video cable shields do not come into direct contact with each other to prevent unintentional local grounding. This can easily occur with cable installed in conduit or cable trays. Tape all connectors in such situations to minimize this risk. Keep camera runs as short as possible with all video cables cut to fit. Excess cable left along any run can increase the risk of interference. Wherever cables share common connection points such as between buildings or in conduit junction boxes take extra care to tape the connectors and cable. At the monitor end make sure all the CCTV equipment is connected to same power point to provide a common local ground.