CleaverBrooks WB, Owner'S Operation And Maintenance Manual

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750-136
Model WB Electric Boiler Manual 1-3
1.3 — Description
The following items are standard on all Cleaver-Brooks Electric Hot Water Boilers:.
Component Description
1. Main Lugs for Supply Circuit Standard boilers are designed for top entry to main power terminals and
are supplied with solderless wire connectors suitable for copper supply
wires. These main lugs are mounted on distribution buses which provide
individual connections for each heating element circuit.
2. Supplemental Internal Protection
Fuses Boilers are provided with supplemental internal protection fuses rated at
approximately 125% of the element circuit load. These current-limiting
cartridge fuses have a minimum 200,000 ampere interrupting capacity to
provide protection for the element circuit wiring.
3. Built-In Magnetic Contactors All boilers use definite purpose magnetic contactors designed for use with
resistance heating loads. Minimum contactor rating is 50 amps resistive
duty rated for 500,000 duty cycles.
4. Heating Elements Standard heating elements are Incoloy sheathed and rated at 75 watts
per square inch (model WB). These elements are individually replaceable
hairpin type.
5. 120 Volt Control Circuit All boilers have 120 volt control circuits. Control circuit transformers with
primary fusing and grounded secondary are provided on all models.
6. Customer Control Interlock Con-
nection A terminal strip is provided on all boilers for connection of the customer’s
external control devices, interlocks, and switches to enable/disable the
boiler, from remote locations.
7. High Temperature Cutoff All standard boilers are supplied with one automatic-resetting, and man-
ual-resetting high temperature cutoff. These are normally set at 235º F
and 240º F respectively, unless otherwise specified. On smaller boilers,
one auto-resetting temperature cutoff is standard as a backup to the limit
duty rated temperature control.
8. Low Water Cutoff (Model WB only) Each boiler is equipped with an automatic resetting electrical low water
cutoff of the probe type.
9. Temperature Control and Tempera-
ture Sensor Boilers with 1 to 4 stages of control are standardly provided with on-off
controls. Larger boilers are provided with a solid state, proportional, mod-
ulating, step-type temperature control system. The temperature control
system controls the input power to the boiler by increasing (or decreasing)
the number of heating element groups (steps) in use as the temperature of
the water returning from the system varies due to system load. The con-
troller switches on or off banks of elements in order to maintain a constant
outlet temperature. Both control systems (on-off and proportional) have
adjustable temperature ranges. The on-off control has a fixed differential
of approximately 5º F. The proportioning control has an adjustable differ-
ential or proportioning range from 3º F to 30º F.
The proportional solid state electronic sequencers also have adjustable
time delay between steps varying from 5 seconds up to 10 minutes.
These adjustable controls enable the boiler to be tuned to the system it
regulates in order to optimize boiler responsiveness and system operation.
The proportional controller also prevents serious electrical damage in the
event of a power interruption. As power is restored to a cool system, the
controller turns on each step in timed sequence until full load is achieved.
This avoids the high current surges that would result if the steps were all
energized at once.