Friday, January 20, 2012

The Lightning's Thief

Contributed by Virginia Fair

Once upon a time a major university installed IP cameras throughout its campus in reaction to a wave of violence perpetrated against female students. All went well until a passing thunderstorm brought a lightning strike which just happened to hit an IP camera mounted on the parapet of a dorm. Of course the camera was destroyed, but have you ever heard the phrase “greased lightning”? It’s a very descriptive term for within seconds, the surge created by the lightning traveled through the network destroying both the server and the switch, creating havoc right down to the network cards in students’ laptops at the end of the cable runs.

Was there any collateral damage? Only if you count the building’s entire IT backbone, including the surveillance system which went down; in monetary terms, over $100,000. But beyond money, the greater loss was the female students’ sense of security. Without the cameras and network recorders they were left vulnerable until replacements could be secured.

How could this be? Was it possible that no one in the affected building had a surge protector in place? They probably did, but calling a lightning strike a power surge is like calling a tsunami a hot tub. It’s been said that lightning never strikes twice but the university was taking no chances. That’s when they realized the need for specialized surge protection. They could then protect their servers, IP cameras, and networks. But first things first, let’s start with a coup le of definitions

Volt
Voltage is a measure of this difference of potential electrical energy. Just as water flows out of a hose because there’s higher pressure at the faucet than at its other end, electric current flows from place to place due to an imbalance. One end of a wire has greater electric potential energy than the other, so, electric current flows from one end to the other.

Power surge
A surge in power occurs whenever the voltage exceeds the designated level, which in the USA is 120 volts and in Europe 240 volts.


Transient Voltage Surge Protectors
A transient voltage surge protector fits between the AC outlet and the equipment it is protecting. These are available with a single outlet or with a number of outlets like a power strip. There are also surge protectors that protect the network, including some that are designed specifically for IP cameras that use PoE.

Most surge protectors have a component called a metal oxide varistor or MOV which connects the hot power line to the outlet’s grounding wire so it can divert excessive voltage away from the device it is protecting. The MOV consists of three parts: a piece of metal oxide in the middle and two semiconductors. The semiconductors connect the hot power wire to the grounding line. The semiconductors have what is called variable resistance that see-saws in depending on the electric current. If the voltage flows below an optimum level, the semiconductors maintain a high resistance, keeping it in the circuit, if it rises above that level, the semiconductors adjust, drops to a lower resistance that dumps the excessive current to ground. If the voltage is correct, the MOV does nothing at all. Surge protectors such as those from Ditek have two modes of operation. In the first, it dumps power to ground. The second kicks in when the power is very high. It then will sacrifice itself by shorting to ground and burning out like a fuse.

Most transient voltage surges are the result of a boost of electrical charge anywhere in the power lines, increasing the electrical potential energy, which in turn increases the flow of current to your wall outlet. The usual suspects are voracious power hogs like air conditioners, elevators, and refrigerators that gobble up a lot of energy when their compressors and motors cycle on and off. Such brief sudden demands for power can upset the voltage flow in the system. Other surges can be attributed to downed power lines, faulty wiring or utility company’s equipment failures. In today’s world, where electricity flows from power plants through a complicated maze of lines, transformers, and more lines to our home and office walls, the possible points of failure are myriad, and any glitch can cause an uneven power flow. So installing a surge protector isn’t a case of preparing for if it’s preparing for when.

The diagram above shows an example of a network system with IP cameras that is protected by various surge devices. More or less surge protectors can be added depending on the environment. One precautionary warning though, is lightning. We travel a slippery slope when it comes to a lightning strike. A direct lightning hit to the wire or device itself will not only fry them but will take out the surge protector, but lightning that strikes nearby causes a surge that can usually be controlled by a surge protector.

Need help with protecting your equipment? We carry a full line of Ditek Gigabit capable protectors. Models range from theMRJPOE, meant for single inputs and protect power, data, and video on up to The DTK-RM16C5 with a 16 port protected panel which can protect a variety of network gear. Also available are 12 port panels compatible with PoE current requirements, and single protectors to protect up to 8 megapixel IP video.


Call us - before lightning strikes. We can be reached at 800-431-1658, 914-944-3425 (outside the USA) or just use our contact form.

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