238-47104-00A - Bradford White

SEQUENCE OF OPERATIONSequence of Operation- Double Element, Non-Simultaneous Operation, 3 Phase.1 21Line voltage is applied across terminals L1& L3 of upper thermostat. Likewise, Linevoltage is applied to terminal L3 of lowerthermostat. ECO in both upper & lowerthermostat is closed, so there is voltage atterminal L4 of both thermostats and to oneside of both upper & lower elements.ECOClosedThermostat closedat terminal T22Tank is cold therefore both thermostatsare closed at terminal T2 (calling for heat).The circuit is complete through the upperthermostat only allowing current to flowthrough the upper element.ECOClosedThermostat closedat terminal T23When the upper thermostat is satisfied, itopens at terminal T2 interrupting currentflow through upper element, and closes atterminal T4 allowing voltage to pass toterminal L1 of lower thermostat. Thiscompletes the circuit through the lowerthermostat allowing current flow throughlower element.Thermostat closedat terminal T43Thermostat closedat terminal T444When the lower thermostat is satisfied, itopens at terminal T2 interrupting thecurrent flow through the lower element. Thesystem is now in stand-by mode waiting forthe next call for heat.5The lower thermostat/element combinationwill generally cycle on and off more oftenthen the upper. In some cases, such as acold tank or in high demand periods, theupper thermostat will call for heat (openingat terminal T4 and closing at terminal T2)prior to the lower thermostat being satisfied.This will interrupt current flow through thelower thermostat and element and allowcurrent to flow through the upper elementonly. When the upper thermostat issatisfied, it resumes operation as describedin sequence #3 above.Thermostat closedat terminal T2Thermostat closedat terminal T25Thermostat openat terminal T2Thermostat closedat terminal T2Page 99