LANtastic by ARTISOFT Artisoft Technical Bulletin TITLE: Networks and Power Considerations FILENAME: POWER.TXT UPDATED: 04.25.95 CLASSIFICATION: AUTHOR: Networking and Power Considerations An often overlooked culprit of network failures is the power being supplied to the network. This is especially true due to the usually false sense of security given when surge suppressors and surge protectors are used. In addition, even a perfect surge protector may not protect your network! Surge Suppression A surge suppressor is a protective device that reduces the amplitude of a surge prior to entering the protected device. It does not eliminate the surge, and does not interrupt power to the protected device. Don't confuse this with a multi-tap power strip, which may look identical, but only provides an additional number of usable outlets. A mult-tap power strip provides no surge protection of any nature. Surge Protection A surge protector, upon sensing an over-voltage condition, will shut down the power to the protected device. The power will remain off until the surge protector is manually reset, or in some cases, physically replaced. It is important to understand that a surge protector is rated by the amplitude and duration of the surge that it can protect against, and by response time. A poorly designed surge protector may shut off the power too late to actually prevent damage! In addition, there will be no protection if the surge is too powerful for the surge protector to handle. The power surges that most surge suppressors/protectors handle are standard power line fluctuations due to the fluctuating load imposed on utility power. Neither one of these devices will protect against a surge caused by a direct, or even a near, lightning strike. In most cases, there is no sure method of protecting from lighting damage, other than disconnecting the power to all computers and equipment in the network. A lightning arrestor may help, but is still no guarantee of absolute protection. Ground Loops and LANtastic 2Mbps Adapters A more common, and less well-known power problem deals with ground-loops. A ground-loop can occur between equipment that has an electrical (wire) connection with another piece of equipment. A network cable can be the electrical connection necessary to create a ground-loop. The actual cause of the problem, though, deals with different ground potentials at each piece of equipment. If ALL electrical equipment in the network is plugged into electrical outlets that are on the same ground/breaker box then ground loops are not a consideration. In the case of networks where the equipment is accessing power from more than one power source [i.e.; different buildings, older buildings, buildings where additions have been made are typical examples] then ground loops will occur under the some conditions. NOTE: Surge protectors, Surge Supressors and UPS devices DO NOT protect your network from ground loops. Ground loops bypass these protective devices since the source of the differing voltage is the ground itself and the voltage does not pass through the device. Common Causes of Ground Loops A computer connected to a true ground through the power cable is connected to second computer via network cable. The second computer is plugged into a different ground source. This may occur in the same building if different breaker boxes feed different power lines. If a power surge occurs via lightning, power company problems, etc, then a difference in the voltage of the different ground sources will cause the voltage to dissipate down the network cabling. This voltage is passed through the network card, and if it is of sufficient power, can burn out the transceiver or another component of the card. The most common cause of differing ground potentials is running cabling for a single network to more than one building. This configuration is not recommended under any circumstances! Using the example given above, but placing the two computers in different buildings, the voltage difference can reach several tens of volts. If network connection is required between buildings, a non-metallic (i.e. fiber-optic, T1 link, infrared) transmission line should be used. Symptoms of Grounding Problems The most common symptom is to have a functioning network one day and the next day [usually after a storm in the area or power company problems] have several of the network adapter cards fail to load the network software or fail to communicate with other nodes on the network. When more than one adapter fails in the same network at the same time by far the most likely cause in ground loop problems. The chances of 2 cards failing in the same network at the same time are VERY remote due to natural causes. Coax Cable and Ground Loops Coax cable is not grounded like 2Mpbs cabling. Coax cabling is considered "floating", i.e. there is no ground. Why then do IEEE802.3 Specifications mandate that a LAN cannot run between buildings [see quote from specification below]? And, why do coax networks experience 2 or more adapters malfunctioning at the same time after some sort of power disturbance. There are 3 basic reasons this can occur: 1] If the two buildings do NOT use a common ground, and ANY part of the network cable, located in either building, accidently touches ground other than the ground in the first building (earth ground), a ground loop can be created. Please note that this can occur in a single building if more than one power souce and ground exist. 2] Incorrect installation where the coax cable IS deliberately grounded at more than one point. 3] Inductance can occur during storms and build voltage on the cable which will discharge along the cable to the point of least resistance - the network adapters. (section 10.7.2.5) "This specification is intended for networks in use within a single building and within an are served by a single low-voltage power distribution system..." ARTISOFT, Inc. makes no warranties as to the completeness or accuracy of this document. LANtastic is a trademark of ARTISOFT, Inc. 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