Sequence Of Operations - Bradford White ElectriFLEX HD CEHD 50 Service Manual

CEHD Series Commercial Electric Water Heaters use an immersion thermostat (contactor models).
The sequence of operation is explained below. It would be impractical to show all wire diagrams
applicable to all configurations. A "typical wiring diagram" is illustrated to aid in understanding the
principles of the operating sequence.
Immersion Thermostat (Contactor Models): Configured to use a single immersion thermostat to
control one or more contactors to energize or de-energize all elements simultaneously. In addition, a
separate high limit switch with manual reset is wired in series with the thermostat. The thermostat
uses a direct immersion bulb inserted into the tank to sense water temperature, while the high limit
switch is surface mounted to sense the temperature of the tank. The immersion thermostat is
mounted to provide temperature adjustment from the exterior of the unit.
Sequence of Operation:
Immersion Thermostat (Contactor Models).
The system has two distinct circuits.
1. Power circuit (shown solid line).
2. Control Circuit (shown dotted line).
1) Line voltage is applied across terminals of fuse
block or a terminal block. Line voltage continues
down and connects to terminals L1, L2 & L3 of
one or more contactors.
A) Contactor is open (no call for heat), so
there is no voltage across terminal T1,
T2 & T3 of contactor.
B) The contactor is controlled by the
control circuit consisting of the
immersion thermostat, Hi Limit Switch
and contactor coil.
2) When the thermostat calls for heat, contacts
close inside the thermostat completing the circuit
through the Hi Limit Switch and energizing the
contactor coil.
3) The energized contactor coil causes the
contactor to close energizing the elements from
terminals T1, T2 & T3 of the contactor.
4) When the temperature setting of the thermostat
is reached, the contacts in the thermostat open.
This interrupts current flow through the control
circuit de-energizing the contactor coil.
5) The de-energized contactor coil causes the
contactor to open, interrupting current flow
through the elements. The heater is now in
stand-by waiting for the next call for heat.

Sequence of Operations

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