Bradford White DB-80R3DS - Manual (Page 8)

SEQUENCE OF OPERATION
Sequence of Operation- Double Element, Simultaneous Operation, Single Phase, 4 wire service installation.
A 4 wire, double element heater wired for simultaneous operation is essentially two single element systems operating
independently. The heaters are wired internally with two independent circuits, one circuit for each thermostat/element
combination. When installed using a two wire service, the blue and red (or white) wires will be connected together,
likewise black and yellow wires will be connected together.
Line voltage from circuit one is applied
across terminals L1 & L3 of the lower
thermostat. Likewise, line voltage from
circuit two is applied across terminals L1 &
L3 of the upper thermostat. ECO in both
upper and lower thermostat is closed, so
there is voltage at terminal L4 of each
thermostat and to one side of the upper and
lower elements.
Tank is cold therefore both thermostats
are closed at terminal T2 (calling for heat).
This completes the circuit through the
thermostats and allows current to flow
through the elements.
1
2
Circuit one
Circuit two 1
ECO
Closed
ECO
Closed
Circuit one
Circuit two 2
Thermostat closed
at terminal T2
Thermostat closed
at terminal T2
When either thermostat is satisfied, it will
open at terminal T2, interrupting current
flow through the corresponding element. As
both thermostats satisfy, the system will be
in stand-by mode waiting for the next call
for heat. Thermostats will operate
independent of the other.
3
Circuit one
Circuit two 3
Thermostat open
at terminal T2
Thermostat open
at terminal T2
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