Lightning and electrical transients are the number-one cause of device failures on electronic equipment. Sentry is specially designed to reduce the effects of transient voltage spikes. Installed properly, the Sentry system will operate failure free for years through most electrical storms.

Lightning usually places large electrical spikes (transients) on power lines, phone lines and all wiring systems. However, lightning is not the only culprit. With special test equipment placed on large residential buildings, electrical transients were found to be common. On average, electrical transients exceeding 3,000 volts could be seen twice an hour and transients more than 6,000 volts occurred twice a day.

All electrical and electronic equipment must withstand this repeated attack.

Lightning will produce transients ten times the levels typically seen, even with distant strikes. A close strike can be devastating to all electrically connected equipment, and a direct strike is sure to cause extensive damage. 

ISOLATION

Certain steps must be followed to assure proper installation.

The Sentry Console (Model HM-550) is similar to a Personal Computer, (PC). Normally, PC's are used on a desk top for one person. Sentry connects this Micro-Controller base to possibly miles of data lines that connect hundreds of apartments. As wiring branches out, the possibility increases that lightning generated electrical transients will get into the system.

The Sentry system layout provides the Sentry Console chassis common ground to be used as the ground reference to the entire system unless data line isolators are used. The ground wire from the data pigtails is connected to the common terminal of the terminal board to make sure this ground reference is common throughout the system. There should be no other ground connections other than at the Sentry Console.

If the data line is to run outside of a building it must be isolated from the Sentry Console using a Sentry Data Isolator (Model HM-696) to make sure no transients can be transferred to the Console. If the run is more than 100 yards or in a known lightning susceptible location it is advisable to isolate the data line at the exit of the building, and at the entrance of the next building. This isolation will require a separate data line for each building being connected to the Sentry Console. The Sentry data lines use differential data signals and are never connected to ground. This data line technology is especially well suited for long distance communication and its ability to withstand transients.

 SUPPRESSION

All Sentry devices are equipped with transient suppressors on both power and data wiring connections. Sometimes the transient will be of an energy level greater than can be suppressed and a component can fail. The most vulnerable components are the data line driver chips. Sentry installs these components into sockets to allow them to be easily changed. The service manuals for the separate devices explain how to make field repairs. Spare parts are available from Sentry.

The Sentry Terminal Board (Models HM-588 and HM-590) has built in suppression for the near end of the cable. It is also beneficial to add additional suppressors (Model HM-884) to the ends of cable runs on the top floor of multistory buildings or at the far end of cable runs on a single story building, insuring there will be adequate suppression maintained along the entire length of the cable run.

 SUMMARY

The chassis ground from the Sentry Console must be connected to the Common terminal of all non-isolated Terminal Boards. Where the data cable exits a building, it must be isolated from the Sentry Console using a Sentry Data Isolator. Additional suppression must be used at the far end of cables on the top floor of all multi-story buildings and at the far end of the longest cable runs on a single story building. If you have any questions concerning the cabling installation, please contact Sentry Manufacturing for assistance.