Transient power spikes or surges can be
introduced into the network from various sources. The IEEE 802.3 Ethemet
standard lists four electrical hazards which networks are susceptible to
during use:
1. Direct contact between local network components and power or lighting circuits
2. Static charge build-up on local network cables and component
3. High-energy transients coupled onto the local network cabling system (those induced by other cables which are installed in the general proximity of network cables)
4. Potential differences between safety grounds to which various network components are connected (such as the slight differences which may be found in safety grounds from one building to another) Spikes can also be caused by fluctuating AC lines, blackouts, or brownouts. They can be passed onto the network by lack of proper spike and surge protection. Networks using unshielded cabling, such as some twisted-pair configurations, are more at risk from the types of spikes described in items 2 and 3 above than are networks using shielded cables. One form of the unshielded twisted-pair network is as an in-house telephone wiring system. These systems can occasionally become miswired and can introduce high-voltage spikes into network components.
Bravo Communications Inc. has introduced a new series of Sure/Fire LAN Protectors that protect expensive LAN components and equipment in high-speed networks from the damaging effects of in-line cable transients such as power spikes and surges. Exposed LAN cables in a typical environment can act as antennae for attracting damaging transients from adjacent high-voltage cables or static build-up on network components. Sure/Fire LAN Protectors guard against the potential loss of integrity caused by failing LAN components. The Sure/Fire LAN Protectors provide secondary protection against transients in LAN components when used in conjunction with primary AC wall outlet surge and power protectors.
The Sure/Fire LAN protectors are designed to be installed at the LAN interface port of the equipment you want to protect, such as network adapter cards, repeaters, tranceivers, wiring hubs, multiplexors, and all related LAN equipment. |
They allow normal network interface signals to flow transparently, but protect against any transient spikes of more than +/- 8 volts by diverting them away from the equipment circuitry to a safety ground. The Bravo LAN protector utilizes a unique printed circuit board design with two tri-polar 10K amp discharge gas tubes in conjunction with a 1500-watt avalanche diode circuit. This combination of circuitry design protects from both the high-voltage AC spikes and the low-voltage DC spikes. All LAN interface pins are connected straight through, pin-to-pin, and all lines are protected with a capacitance of less than 8pf at zero bias. A red diamond-shaped protection light will illuminate when the unit is properly installed, indicating that the LAN protector is active. This feature also serves well as a troubleshooting aid in analyzing LAN segment fault conditions. If this light remains off, the unit has sacrificed itself due to a transient spike, and must be replaced to restore protection from future spikes and functionality to the network node.
Sure/Fire LAN Protectors come in two different models. The BNC/LAN and the RJ45/LAN. Both models retail for $59 each. You can use the BNC/LAN model on all Ethernet/Thinnet, Arcnet, or Token-Ring BNC ports. It will also work on any IBM 3270-type BNC connections. The unit is easily installed at the network interface port. The red diamond-shaped LED will not illuminate unless the grounding strap has been connected to a proper ground. In networks where the normal signal voltage used does not exceed 2.5 volts, the LED feature will not function, but the protection circuitry will. This information should have been added to the documentation. The unit functions as advertised by stopping induced voltage spikes from reaching the interface port circuitry, both low-level DC and high-level AC. After applying a low-level DC voltage spike onto the line (+12 volts), |
the protection circuitry was still active, but the LED circuitry was destroyed. With the LED circuitry destroyed, the LED was no longer illuminated, which is supposed to indicate that the unit is not providing protection. According to Bravo President Dennis Mozingo, the LED circuitry has been changed, correcting this problem in all future production units. The case housing the BNC/LAN model was made of plastic. For the same reasons that shielded cables provide more protection than unshielded cables, I believe a metal case would be better. You can use the RJ45/LAN model on the twisted-pair type Ethernet (l0 Base-T) and Arcnet ports using the RJ45 type connectors. This unit is housed in a shielded metal casing, with the same protective circuitry as found in the BNC/LAN model. This unit is also easily and quickly installed on any node on the network. The protection circuitry design is basically the same as the BNC/LAN model, and operates in the same ways as described above.
Using surge protection could be compared to buying insurance on your investments. Network managers must decide what levels of protection they require, and what nodes of their networks warrant spending the extra money for the added protection provided by such devices as the Sure/Fire LAN protectors. Each network environment is unique. Some networks are installed in environments which are not extremely susceptible to transient spikes and require no more protection than given by twisted-pair or shielded cabling. Other networks may be installed in harsh environments where transient spikes are often a problem, such as in a factory with high-voltage lines and heavy equipment running. If you decide that your network could benefit from surge protection on the network data lines, the Sure/Fire LAN Protectors are a sound choice. They are competitively priced with other such devices on the market, and have the distinction of being the only protectors I could find using the tri-polar gas tube/avalanche diode design. |
Reprinted with permission from LAN TIMES, July 8, 1993 Copyright 1993 by McGrawHill, Inc. All Rights Reserved.
Copyright © 1996 Bravo Communications, Inc. All Rights Reserved.