Published In June 2001
There are two worlds of overcurrent and overvoltage. The first is with AC power. The second is for twisted pair copper and the other lines, which are used in telephony and computer networks. It is the latter that we’ll cover here. Twisted pair lines can pick up an induced spike or overcurrent situation, perhaps induced when an electric line comes over a telephone line. An electrical contractor needs four basic skills to move to the low-voltage protection world. First, according to Ed Fontana, system engineer with Tyco Electronics Power Systems, Mesquite, Texas (www.power.tycoelectronics.com) is recognizing what equipment is required to do a job. Next is having the equipment on-site when needed. A good contractor will know how to install and qualify the equipment as safe and operational. Last, and maybe the most tricky, is knowing how to win contracts that are within the firm’s competence level. Standards are a good place to start. Two basic standards come into play when protecting these systems. The first is UL-1459, which addresses power concerns from the end-user’s point of view. The second is the FCC’s Part 68, which deals with protecting the telephone network. Both of those specifications have been around for a long, long time. Early on, gas tubes were used to protect such systems. Later, metal oxide varistors (MOVs) took the forefront. MOVs are basically voltage-dependent resistors. They absorb voltage and current surges or spikes. “They worked well, but with every hit they would degrade,” noted David Lark, marketing manager with Teccor Electronics, Irving, Texas (www.teccor.com). “A 300-volt MOV eventually could overshoot to 600 volts.” That is hardly effective protection. More recently, companies are taking a solid-state thyristor approach. A product like the Teccor SidACtor makes use of voltage breakdown on the thyristor, giving highly controlled, consistent protection. Units are available from 30 to 400 volts, with 300 being typical for protecting phone circuits. Telephone lines typically are -48 volts DC, but the ring voltage will be clipped with a unit like a 60-volt protection system. “The thyristor switches in less than a nanosecond,” Lark said. “It is predictable and overshoot is minimal.” When the trigger voltage is exceeded, energy is dissipated in the copper wires. The unit will reset itself when the current goes away. Lark says both primary and secondary physical locations are needed for complete protection. The primary is placed at the point of entry into the building. Everything else is secondary protection, including protection of line cards. A four-channel line card will have one protector for each line. “Modems need protection, whether it is a Personal Computer Memory Card International Association (PCMCIA) modem or a gas station’s pump with its point of sale (POS) modem for credit cards,” Lark continued. Most of those units are protected by surface-mounted protection, which sits right on the computer card. This is out of the realm of most installers. It simply comes as part of the package. Let’s get physical Physical connectivity is as important as redundancy. It seems redundant to emphasize that all wiring has to be tightened down, but that is a common cause of failure, according to Henry Lengefeld, senior staff engineer with American Power Conversion’s (www. apcc.com, West Kingston, R.I.) enterprise systems group. He is based in Raleigh, NC. “It’s one of those tests you have to do annually,” he said. “In a critical data center it should not be put off.” One way to avoid having to take the system off-line is to use an infrared camera to check for hot spots, then decide how urgent the situation is. Lengefeld recommends checking compatibility of the engine-generator with the UPS. “The contractor must be sure it is sized to the UPS,” he says. The closer it is to a 1.0 power factor, the better. Contractors should look for a UPS with low input harmonics, as well. Hook up customers to a system which gives a “soft start” so the power can come up in a controlled fashion. Try to provide as much power backup as possible in a single package. “One large system is easier to maintain and to service,” noted Winston Jagassar, director of distribution for MGE Systems, Costa Mesa, Calif. (www.mgeups.com). They produce a wide range of UPS systems. Another thing to keep in mind, especially when protecting telephone lines, is that the tip and ring may or may not be grounded. “Digital subscriber lines (DSL), especially, tend not to be grounded,” Lark said. Digital lines have three places where there can be a potential difference: between tip and ring, between ground and tip, and between ground and ring. Companies like Leviton Manufacturing, Little Neck, N.Y., offer 19-inch rack-mounted surge protectors. Their latest line offers point-of-use transient voltage surge suppression for rack-mounted equipment. Each has 12 protected receptacles, 10 in back and two on front. Models are available with either 15- or 20-amp receptacle ratings and choice of straight-blade or locking plug. It is important to know where to place either surge protection or power backup. According to Invensys, if a UPS appears to be the ideal solution, you’ll be choosing between online and offline typologies. Online is either double conversion or single conversion (sometimes called Delta conversion). Offline can be standby or line interactive. Online typology UPS products are preferable for factory automation applications, while offline UPSs are more commonly used for office environment computer applications. According to Invensys, double-conversion UPS has been proven to be the most reliable solution for isolating input transients, regulating the output frequency, and providing the purest output 100 percent of the time. Such units are available as small as 500VA to sizes rated in the multi-megawatts. Invensys offers a complete line of double-conversion UPSs for information technology (IT) managers in its Axxium Pro line. The system can be provided with more than one backup unit and can be daisy-chained by adding additional modules. Jagassar would agree that larger, online systems are preferable for critical applications. He notes that, with a small offline system, there always will be questions over time about the reliability of the unit’s battery. Most often, those questions are not resolved until problems hit. Then, it’s too late. According to Invensys, single-conversion UPS units do not offer the same protection from transients as double-conversion ones, but typically are a bit more efficient in operation; thus a savings on the electric bill. However, efficiencies in the design of double-conversion units are closing the gap. Fontana noted that the old 99.999 percent reliability is no longer enough. “Some people want 10 nines,” he quipped. Yet there are sites with 10 750kVa UPS capacity and a significant amount of DC backup as well. Tyco has both DC and AC systems, and recently has been doing more work with the DC. “DC solutions are acknowledged as more reliable,” Fontana said. In December, Tyco introduced the NP1200, a bridge between modern voice/data/video networking equipment requiring 448V DC and the standard parts that electrical contractors use every day. “Most power products are designed by looking inward at a particular need of a specific customer who may have a precise number of line cards or ports that they want to power,” Fontana said. The customer then looks at power supply for the project. Tyco took a different approach with the NP1200, looking at its market as 15A to 120V AC branch circuits, not routers or switches. “Instead of looking at the load equipment, we looked at building infrastructure—the parts that electrical contractors use every day,” he continued. “We then optimized the product based on the parts contractors carry on their trucks, with the idea that one day the NP1200 would be the AC-to-DC power supply on the service and installation truck. The NP1200-3 Rectifier is designed to fully use or exactly match a 120V/15A circuit with full National Electrical Code (NEC) and Underwriters Laboratories (UL) compliance. It includes three NP1200s and a power shelf, fitting a 19-inch rack and requiring two-rack units (3.5 inches) height and 1-foot depth. One NP is designed to use a single 30A/208-240 VAC branch circuit. For inside and testing uses, Lambda Electronics, San Diego, Calif., (www.lambdapower.com) has its Z-up Series, which guarantees laboratory performance applications accurate voltage and current programming stability when interfacing equipment with the power supply. Most UPS systems come with a 5- to 10-minute standard run time. For extended runtime, a bank of external battery cabinets will be required. Keep it efficient Be aware of the efficiency of the system being protected, especially in the computer world. It will help cut the overall number of UPS systems that must be purchased and installed. In the past, computer equipment power supplies have been rated at 0.6 or 0.8 power factor (PF). “This number is indicative of the amount of real power (or watts) being used,” said Ron Mann, director of engineering for the rack and power systems group of Compaq Computer Corp., Houston, Texas (www.compaq.com/ups). Anything less than a power factor of 1.0 is lost in the form of heat. Therefore, an efficient piece of equipment is rated close to 1.0—or unity power. “An inefficient piece of equipment rated at 0.6 PF or 0.8 PF is wasting 0.4 (40 percent) or 0.2 (20 percent) electricity respectively. Using efficient power factor coefficient (PFC) uninterruptible power systems can protect up to twice the number of servers in a typical configuration when compared to non-PFC UPSs,” Mann added. Lengefeld also says contractors should alert customers (especially in areas like California where extended blackouts are more common) to provide fuel for extended use of the generator. An efficient UPS will extend generator time. The engine can be smaller, or run longer, on a Delta conversion unit with its unity power-factor conversion, instead of requiring the typical two-to-three times UPS load on less efficient units. “A 100kW UPS ideally needs 130 to 150kW as compared to 200-300,” he said. Not only should power equipment be efficient electronically, but it also should be able to grow efficiently as the operation grows. Invensys emphasizes the importance of buying a scalable unit. This allows users to add to the system as their power needs grow. Rather than replacing an existing UPS with a larger unit to handle the increased load, scalable UPSs can be paralleled together, increasing capacity. A secondary benefit of scalable UPS is the redundant protection provided for mission- critical applications. By paralleling several units together, one of the units can serve as a backup to any of the others in the event of a UPS system failure. HARLER, a contributing editor to Electrical Contractor, is based in Strongsville, Ohio. He can be reached at (440) 238-4556 or firstname.lastname@example.org.