April showers bring May flowers, or so goes the old cliché. Warmer weather also brings with it thunderstorms and power surges galore. All too often the result is false alarms, lost data and the destruction of high-tech electronic equipment.
Although lightning is a major concern during good weather, it doesn't have to be warm out for electric motors, smelting operations, heavy industry and other electrical concerns to spell big trouble for the equipment for which fire and burglar alarm technicians are responsible.
Lightning is a common concern for alarm technicians because of the suddenness with which it can strike. The damage that it can cause may involve a lone device connected to an internal low-voltage cable, like an addressable manual fire pull or an individual circuit board. Or it might involve an entire motherboard within a fire or burglar alarm panel.
Sometimes the damage is light while other times it can be catastrophic, tearing through the system from one end to the other. Having a fair understanding of how lightning works and by using good installation practices, along with quality equipment, technicians can limit the amount of damage that does occur.
Mechanics of a Lightning Strike
Any device that connects to a metallic wire can suffer damage at the hand of lightning. This is true whether the strike is direct to the cable itself or indirect by virtue of inductance. Sometimes no matter what you do, lightning will do irreparable harm.
Concerning a direct hit to equipment, lightning can enter through multiple paths from outside the structure. A good example is a campus environment where there are many buildings.
Lightning also can enter the structure through the public electric bus via outside power lines or one of the many paid subscription services now available. Examples include conventional telephone, cable television networks and satellite dish systems.
In a burglar or fire alarm system, once lightning enters the equipment through one of the methods cited above it can migrate to a signaling line circuit (SLC), initiating device circuit (IDC), notification appliance circuit (NAC) or some other low-voltage line. Another example is the coaxial cable or twisted pair unshielded wire that carries video images in a CCTV system.
"The focus is usually on SLC loops [burglar and fire alarms], low-voltage data [networks] and coax cable [CCTV].
Manufacturers are well aware of the problem lightning poses and for this reason they commonly build a limited amount of surge protection into their electronic systems at the point of manufacture. In most cases this is done right on the motherboard itself.
This ploy most often includes add-on printed circuit (PC) boards and any number of subsystems, such as smoke detectors, glass breakage sensors and others. And yet damage or total destruction can and often does occur when lightning appears on the scene.
One fire alarm manufacturer uses optical isolation on the data loops to minimize lightning damage. Damage in this case often occurs when lightning induces a high voltage current in the internal wiring of a building. This can be especially problematic in campus environments where data lines travel under ground between buildings.
This design incorporates the idea of isolating the grounding differential from the other buildings. Nice little spark gaps and it does help, but the problem is, when incorporating second-rate surge suppression, you get a feedback loop up the case ground into the smart chip.
When you consider the multiple pathways over which lightning can travel, you must also think about distance with regard to proximity as it pertains to the surge protection device that acts to clamp the surge voltage and route the strike current to earth ground.
This is true whether it involves external surge protection or those internal to the device itself. Many years ago an engineer told this writer that lightning will often travel well beyond the point where the surge voltage is clamped. All too often this ends up damaging critical circuits, not to mention the possibility of arcing within the panel itself.
The most panels can handle some of this current, but not all of it. This is especially true where there's a significant voltage differential between equipment grounds of all the interconnected equipment.
Think Ahead When Installing
As mentioned earlier, one common application where lightning can cause considerable damage involves integrated systems across multiple buildings. Because of the matrix of wires that travel to and from each building, being installed either overhead or underground, the propensity for damage is considerable.
In this case a single head-end system may be employed to provide a number of low-voltage services, such as fire, security and/or CCTV protection. Here, especially proper precautions must be taken, such as the use of quality surge protection.
One case in point is a motel with multiple buildings serviced in the summer of 2008, by Nick Markowitz, owner of Markowitz Electric Protection of Verona, Pa. According to Markowitz, the location experienced a lightning strike that damaged a fire alarm system, three cameras and a washing machine. The lightning affected systems in three separate buildings by first entering a restaurant and then traveling throughout the entire campus.
"The camera system is one of those cheap cameras-in-a-box deals that uses four-wire telephone cable. One of the cameras is located in the restaurant and is fine, but another one took a hit and the wiring was damaged," says Markowitz. "The other two cameras were converted from phone wire to inline powered coax and lightning took out the converters and power injectors."
Lightning entered through one of the cables that crossed between the buildings, Markowitz reports. A close examination revealed that there wasn't any surge protection on any of the low-voltage cables that serves video or any other centralized system. And yet damage was spotty, which Markowitz found puzzling considering the severity of the hit.
"I find it strange that the monitor and one of the other cameras were fine but all the rest was trashed. Usually when lighting strikes like this, everything goes at once," he adds.
Equipment Circuit Design Changes
Manufacturers have changed the way they construct and package components contained in their low-voltage systems. Included is the way those components are installed on PC boards. Both of these factors have altered the way alarm technicians protect their electronic systems from lightning, says Pecore.
"In 1997, Stormin Protection Products officially became an engineered lead business because the projected sales in the area of low-voltage surge suppression for fire alarm, CCTV and access control systems will be in greater demand as the progress of SMT [surface-mount technology] literally took over the industry," says Pecore.
SMT technology allows manufacturers to reduce power consumption as well as extend the length of time batteries will provide backup power. If nothing else SMT components have allowed manufacturers to reduce battery size to meet a specific code requirement, such as standby time. SMT technology poses a problem because it represents a relatively low impedance to lightning.
“SMT technology for an old guy is a dirty word. It spells out one thing, nothing but trouble,” says Pecore. “Manufacturers took all the linear and high capacitance devices off the board and left me with a featherweight that if I hiccup just right, it will blow.”
Design engineers have eliminated linear power supplies, replacing them with Wheatstone bridges. Also, low-impedance capacitors and resistors have replaced heavy-duty capacitors and resistors, and smart chips have replaced entire printed circuit boards.
“Low Pico Farad devices have also replaced other components — all for the sake of reducing current draw,” says Pecore. “As a result of these changes, fire alarm panels (and other electronic systems) have become more susceptible to surges, impulses and ground strikes.”
The idea is to raise the impedance of the panel, not lower it, and to do this the installer has to look for ways to create an alternate path that looks more inviting to high-voltage lightning than the panel’s motherboard.
According to Pecore, the answer is an inline series hybrid three-stage, two-tank circuit that works to impede strike current while shunting it to ground. This is accomplished by focusing on the characteristic frequency associated with lightning.
Thanks to SSI Magazine FOR HELP & Thanks to John Pecore, President at Stormin Protection Products Inc
