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KELCO T20 Installation & Programming Instructions
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Contents
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The HD (Heavy Duty) TerminalThe HD terminal must be left unused or onlyever be linked to the relay terminal Relay 1 Nor-mally Open. It must never be used for any otherpurpose and it must never be connected to anyexternal device. Under no circumstances con-nect the HD terminal to the terminals of Relay 2.The HD terminal must be regarded as live at alltimes and at full mains potentialWARNINGThe T20 timer contains a solid-state switch (HD Heavy Duty drive) that can beused to protect the contacts of Relay 1 by eliminating the destructive arcingcaused by the starting and stopping of pump motors. The solid-state switch isaccessible from the HD (Heavy Duty) terminal on the terminal block. We recom-mend the HD drive be used whenever the timer is used to directly control a pumpmotor. The HD drive should not be used when the T20 is connected to externaltimers, contactors, relays or to any other external device where voltage free con-tacts are required. It is strictly intended for the direct control of highly inductiveAC motor loads. The HD terminal and the timer’s built in relays must never beconnected to a DC motor under any circumstances.When the HD terminal is linked to the terminal Relay 1 Normally Open, the HDdrive in effect parallels a 40Amp solid state switch across the relay’s normallyopen contacts. This increases the momentary current carrying capacity of therelay’s contacts to well over 70 Amps. The solid state HD drive is only activatedfor a short period when the pump starts and stops. It effectively handles the highinrush current associated with the pump starting, and it provides a current path forthe destructive back EMF associated with the pump motor stopping.To use the HD drive place a heavy link wire, 1.0mm or 1.5mm Sq between the HDterminal and the Normally Open terminal of Relay 1.8 |
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