238-47104-00A - Bradford White

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SEQUENCE OF OPERATIONResidential and light duty commercial electric water heaters are designed to operate using several different operatingmodes. The common modes and sequence of operation are as follows:1. Single Element Operation.2. Double Element Non-Simultaneous Operation (single phase).3. Double Element Non-Simultaneous Operation (3 phase).4. Double Element Simultaneous Operation (single phase).5. Double Element Simultaneous Operation (3 phase).Sequence of Operation- Single Element Operation.1Line voltage is applied across terminalsL1 &L3 of the thermostat. ECO isclosed, so there is voltage at terminal L4and to one side of the element.1ECOClosed2Tank is cold therefore thermostatis closed at terminal T2 (calling for heat).This completes the circuit and allowscurrent to flow through the element.2Thermostat closedat terminal T23When the thermostat is satisfied, it opens atterminal T2 interrupting current flow through theelement. System is now in stand-by mode, waitingfor the next call for heat.Thermostat opensat terminal T23Page 66
SEQUENCE OF OPERATIONNon-Simultaneous and Simultaneous OperationDouble element electric water heaters are designed to operate in a Non-Simultaneous or Simultaneous mode.Non-Simultaneous Mode: Allows only one heating element to operate at a time. For example, when the tank is cold,the upper element is energized first, heating the top of the tank. Only when the upper thermostat is satisfied, the upperelement is de-energized and power is directed to the lower thermostat, energizing the lower element and heating thebottom portion of the tank until the lower thermostat is satisfied. As hot water is drawn off the tank, it is replaced withcold water delivered through the dip tube to the bottom of the tank. The bottom of the tank cools, the lower thermostatwill call for heat energizing the lower element. If enough hot water is drawn from the tank, the top portion of the tankcools and the upper thermostat will call for heat, de-energizing the lower element and allowing only the top element toenergize until the upper thermostat is satisfied.Simultaneous mode: allows both heating elements to operate at the same time. That is, if either thermostat (upper orlower) is calling for heat, the corresponding heating element is energized independent of the other.Sequence of Operation- Double Element, Non-Simultaneous Operation, Single Phase.1234Line voltage is applied across terminalsL1 & L3 of the upper thermostat. ECO isclosed, so there is voltage at terminal L4and to one side of the upper and lowerelements.Tank is cold therefore both thermostatsare closed at terminal T2 & 2 (calling for heat). Thecircuit is complete through the upper thermostatonly, allowing current to flow through upperelement.When upper thermostat is satisfied, it opens atterminal T2 interrupting current flow through upperelement, and closes at terminal T4 allowing voltageto pass to terminal 1 of lower thermostat. Thiscompletes the circuit through the lower thermostatand allows current flow through lower element.When the lower thermostat is satisfied, it opens atterminal 2 interrupting current flow through lowerelement. The system is now in stand-by modewaiting for the next call for heat1 2UpperT’statUpperElementLowerT’statLowerElementECOClosedThermostat closedat terminal T2Thermostat closedat terminal 2UpperT’statUpperElementLowerT’statLowerElement5The lower thermostat/elementcombination will generallycycle on and off more oftenthen the upper. In some cases,such as a cold tank or in highdemand periods, the upperthermostat will call for heat(opening at terminalT4 and closing atterminal T2) prior to the lowerthermostat being satisfied. Thiswill interrupt current flowthrough the lower thermostatand element and allow currentto flow through the upperelement only. When the upperthermostat is satisfied, itresumes operation asdescribed in sequence #3above.Thermostat closedat terminal T43UpperT’statUpperElementLowerT’statLowerElementThermostat openbetween terminals1 and 24UpperT’statUpperElementLowerT’statLowerElementThermostat closedat terminal T2Thermostat closedbetween terminals1 and 25UpperT’statUpperElementLowerT’statLowerElementPage 77
Page 1 and 2: RESIDENTIAL ELECTRIC AND LIGHT DUTY
Page 3 and 4: GENERAL INFORMATIONCommonly Used Fo
Page 5: GENERAL INFORMATIONSurface Mounted
Page 9 and 10: SEQUENCE OF OPERATIONSequence of Op
Page 11 and 12: SEQUENCE OF OPERATIONSome electric
Page 13 and 14: TROUBLESHOOTINGQuick Step Plan to H
Page 15 and 16: SERVICE PROCEDURE RE-IIHeating Elem
Page 17 and 18: SERVICE PROCEDURE RE-IIIResidential
Page 25 and 26: SERVICE PROCEDURE RE-IVLight Duty C
Page 33 and 34: SERVICE PROCEDURE RE-VThermostat Re
Page 35 and 36: SERVICE PROCEDURE RE-VIIDip Tube an
Page 37 and 38: NOTES37
Page 39 and 40: NOTES39

238-47104-00A - Bradford White

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