UFC 3 -430-11
14 February 2001
utilized, the design must contain a PLC for safety shutd own that is separate and
independent of the one used for boiler control.
3-5.3.4 Special Considerations. Special attention should be maintained throughout
the boiler design to prevent the following safety hazards.
Equipment must be designed to prote ct against electrical shock from
exposure to control power.
Boiler control must assure a sufficient quantity and duration of pre-purge
airflow through the boiler prior to ignition to prevent boiler explosions.
Boiler control must assure a sufficient quantity and duration of post-purge
airflow through the boiler during shutdown to prevent boiler explosions.
Boiler control must assure a sufficient quantity of combustion air and
prevent excessive fuel during boiler operation to prevent boiler explo sions.
Boiler control must limit the number of retries when igniting the boiler pilot.
The industry standard is to allow three attempts at achieving pilot ignition
prior to necessitating a boiler purge cycle.
3-6
HARDWARE. Hardware standards are defined by NEMA -ICS 2, Standards
for Industrial Control and System Controllers, Contractors, and Overload Relays Rated
Not More Than 2000 Volts AC or 750 Volts DC.
3-7
EQUIPMENT RATING AND CLASSIFICATION. Provide instruments that
are rated for the environme nt. Electrical components must be designed for the
anticipated temperature and humidity inside of the enclosure, fungus proofing where
required, and vibration. Refer to NEMA -ICS 1.1, Safety Guidelines for the Application,
Installation, and Maintenance of Solid State Control for additional information.
3-7.1
Enclosures. Enclosures must be certified by the National Electrical
Manufacturers Association (NEMA) for the environment where they will be used. NEMA
4 enclosures must be used for outdoor locations . Use NEMA 4X enclosures in
corrosive environments. A space heater is required where condensation of moisture is
a problem.
Enclosure ratings are defined by NEMA -250, Enclosures for Electrical
Equipment (1000 Volts Maximum), and NEMA-ICS 6, Enclosures for Industrial Controls
and Systems. Enclosure ratings are summarized in Table 3 -1.
3-3
Previous Page
