to the irregularities of the hopper surface, providing intimate contact
between the heaters and the hopper, and providing maximum heat transfer.
Hopper heaters shall be of low watt density design (maximum of three watts
per 645 square mm square inch of resistance element) with a minimum of six
parallel resistance paths per heater (continuous blanket type elements
shall be deemed to meet the multipath requirement). Each heating element
in the module shall be capable of being operated at 2152 watts per square
meter 200 watts per square foot. Heating elements shall be made of 600
series stainless steel alloy or nichrome encased in a 20 gage minimum
aluminum or aluminized steel mounting pan or casing. Cold lead wires and
interconnecting wires shall be multistrand copper wire with high temperature
(454 degrees C) (850 degrees F) insulation. Cold leads shall be furnished
with strain relief constructed in such a manner as to prevent damage to the
heater modules due to rough handling. Leads shall be of sufficient length
to reach the terminal box. Splices shall not be permitted in leads from
modules, tapes, or blankets to the terminal box. Each module, blanket, or
tape shall be tested for electrical integrity at 1,000 volts prior to
installation. Individual modules shall be designed to fit between the
hopper stiffeners and other hopper well obstructions to provide the maximum
coverage possible. Heating units supplied shall have metal labels firmly
attached to the unit listing the wattage and voltage of the unit. Heating
units and mounting hardware shall be constructed of high temperature
materials capable of withstanding 454 degrees C 850 degrees F. Heating
units shall be insulated with high temperature woven glass cloth or mineral
fiber. Mica or magnesium oxide insulated heaters shall not be provided.
Cold leads from each heater shall be provided for external circuit
connection. The cold leads shall be contained in hot-dip galvanized NEMA
Type 4, as defined in NEMA ICS 6, cast iron fitting for connection to field
installed solid conduit or waterproof raceway. NEMA 4 as defined in NEMA
ICS 6 hopper heater terminal boxes with terminal blocks for connection to
heater leads and thermostat leads shall be provided. Terminal blocks in
each terminal box shall contain a sufficient number of terminals to connect
the heaters for each hopper, one control thermostat, and one low
temperature alarm thermostat. The thermostats for monitoring hopper
temperature shall be 120 volts AC adjustable type in NEMA 4 enclosures.
Each hopper heater terminal box, fed from a panel, shall include one 3-pole
fused main switch, magnetic contractor and alarm relay with two normally
open contacts, terminal blocks for power, control and alarm circuits, a
fused control transformer having a 120-volt secondary, and auxiliary relays
for automatic operation of the heater system. The cover shall have the
following devices mounted, for each contractor: "HAND," "OFF," "AUTO"
selector switch.
a.
120 volt red light--"ON" with integral transformer.
b.
120 volt white light--"LO TEMP" alarm with integral transformer.
c.
Device and enclosure nameplates.
The following components shall be provided for each fabric filter baghouse
for thermostatic control of the hopper heater system:
a.
A master hopper heater control panel.
b.
Hopper heater terminal panels at each hopper. The contractor
shall furnish materials, tools, and labor required for connections
of circuits and wiring between local hopper heater control panels
and the master heater control panel.
SECTION 15864N
Page 51
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