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Lightning and surge protection: when to use a UPS and when to use lightning or surge protection on your security systems

Is a UPS adequate lightning protection? Often, when involved in site surveys, we find customers quite content with their UPS as their ultimate means of lightning and surge protection. A UPS is exactly what it stands for: an uninterruptible power supply, and should be used against over voltage conditions, brown outs and power failures. A UPS is there to ensure that relevant parts of your CCTV or security network continue to operate even during a power failure. Although there is some surge protection on the majority of UPSs it is almost always inadequate in a heavy transient environment.

Let me explain. You do not want your expensive UPS taking knocks from transients like lightning and surges as eventually it will fail, very probably the next time you have a power failure. A UPS and lightning/surge protection should be viewed as two separate parts of the protection solution. The UPS is there to give you backup power in the event of a power failure. Lightning/surge protection is there to protect equipment from any one of a number of electrical anomalies that can damage equipment. Both of these are very important for a CCTV or security system where you simply cannot afford any downtime whatsoever.

CCTV and security equipment needs special protection and not just power protection. Often people only consider power when protecting their security systems against lightning. We need to remember that when a nearby lightning strike occurs there is a change in current over a change in time (di/dt) which results in an electromagnetic field being generated. This electromagnetic field can induce voltages in nearby copper cabling which can potentially damage equipment on either end of this cable. This cable is quite often the coaxial video cable that links the CCTV cameras (Figure 1) to the DVR or multiplexer.

Figure 1. Protecting a static CCTV camera

Can you see that in this circumstance the lightning did not affect the power but actually entered the security network through the CCTV video cables? The same is possible for the RS485 (data) link running to a PTZ (Figure 2) camera and RS485 links running outdoors on access control networks. What this means is that to protect any system adequately you need to protect the video input/output, data connection as well as incoming power.

Figure 2. Protecting a PTZ (pan, tilt and zoom) camera

Earthing

It is also very important to always ensure that any protection devices you use are connected to electrical earth with good continuity to the star point of the mains transformer. Never have a separate earthing system, additional earthing systems have their merits but always ensure that they are bonded to electrical earth.

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