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Electrode Boiler
Before any water treatment program is implemented, a complete water analysis
should be provided to Cleaver-Brooks for review.
4 - Electrical Systems
The three electrical systems are described in this section, which gives a general outline of the basic
circuits and their functions. The power supply circuits (high and medium voltage) are diagrammed on
the power wiring schematic in the boiler drawings, and the boiler control circuits are diagrammed on
the 120V control wiring schematic.
4.1-High voltage power supply
The high voltage power supply, to be connected by the customer, is a three-phase, four-wire 'Y'
connected configuration. A full sized insulated and shielded neutral is required in this circuit, as it must
be of adequate capacity to take a sizeable amount of current in the case of a large phase unbalance
or fault condition. This circuit must include a high voltage main circuit breaker, current transformers
(one per phase for supply monitoring), and an isolating switch or mechanism, as required by the
National Electrical Code and local codes which may apply. The main circuit breaker must include a
common trip device which may be actuated to open the circuit breaker in response to supply circuit
supervisory relays or boiler limit circuits. Potential transformers are required for voltage monitoring.
The breaker must also have a normally open auxiliary contact for connection to the boiler control
circuits. If the main circuit breaker is located some distance from the boiler, local codes may require
the installation of a high voltage isolating switch at or near the boiler for local isolation.
Main connection
From the main circuit breaker, the four-wire voltage supply circuit is brought to the boiler by the
customer and terminated at the electrodes and at the neutral lug on the boiler shell inside the electrode
terminal enclosure. The ground lug is on the bottom of the casing ring. The boiler ground should have
the same capacity as the supply conductors. Access to the terminal enclosures must be interlocked
with the customer 's main circuit breaker and/or isolating switches to prevent access to the electrodes
when the power supply circuit is energized.
High voltage supply circuit supervisory relays
Proper monitoring of the high voltage supply circuit requires the use of a supervisory metering system.
This system monitors signals from the supply circuit current transformers and actuates the common
trip device on the customer's main circuit breaker in the event of ground fault, over-current, loss of
phase, or phase unbalance.
If unbalance, ground fault, or overcurrent occurs, the supervisory relay system may also signal the
limit circuit and shut the boiler down. The supervisory system is a required part of a boiler
installation and must be included (either factory-installed in the boiler control panel and/or included
with the customer supplied and wired high voltage switchgear)
12
Caution
!
Notice
750-272
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