WIRING (cont’d.)
11.Delta Connections — When heaters occur in multiples of three, they may be connected to, and balanced across, three- phase lines. The most commonly used connection is the delta connection illustrated in Fig. 5. Three phase Delta connections to minimize inductive effect in conduits are made per this dia- gram. The rule: run all 3
Figure 5 |
OPERATION
FIRE/EXPOSION HAZARD. This heater is not intended for use in hazardous atmospheres where flammable vapors, gases, liquids or other com- bustible atmospheres are present as defined in the National Electrical Code.Failure to comply can result in personal injury or property damage.
Before energizing this heater:
1.Be sure all electrical connections are tightly made. Hold ter- minal with pliers when tightening screw.
2.Be sure that all conductors are properly insulated.
3.Be sure that all element assemblies have been properly replaced, and that secondary insulation bushings have not been omitted.
A.Controlling Radiant Intensity
Standard Radiant heaters are built to operate at 40 watts per sq. inch on the element sheath. When it is desired to reduce radiant intensity, one or more of the following methods may be used.
1.INPUT CONTROLLERS. These
2.SOLID STATE THYRISTOR POWER CONTROLLERS. For best
B.Maximum Ambient Temperatures
Chromalox Radiant Heaters are not recommended for applica- tions in ambient temperatures exceeding 450°F. Higher ambi- ent temperatures mean shorter heater life.
Maximum work temperature in a given time depends on sever- al factors: Reflectivity of work, specific heat of work, mass of work, kW input and losses from oven, and time of exposure. As work temperature increases, the work loses heat by radiation and by convection to the surrounding ambient. Although it is a general principle of Radiant Heater application that work tem- perature conventionally exceeds ambient temperature, in cases where extremely high work temperatures are desired, it is nec- essary to enclose the heaters in order to increase the ambient. If evaporation of a liquid is desired as a result of increasing work temperature, it is necessary to provide ventilation air in order to carry away the evaporated liquid. Under carefully engineered circumstances, a maximum work temperature of 600°F may be attained.
MAINTENANCE
ELECTRIC SHOCK HAZARD. Disconnect all power before installing or servicing heater. Failure to do so could result in personal injury or property dam- age. Heater must be installed or serviced by a qualified person in accordance with the National Electrical Code, NFPA 70.
A. To Remove Heating Element
1.Remove terminal cover screws and terminal cover.
2.Disconnect heating element from electrical leads at both ends.
3.Remove screws from porcelain terminal blocks.
4.Remove element support clips and secondary insulating bushings.
5.Lift out elements.
B.To Install Element
Observe instructions for removing elements and proceed in reverse fashion. Be sure to replace secondary insulating bushings.
C.Care of Reflectors
Reflectors should be cleaned periodically. A mild soap and water solution or fine cleaning powder is best although more drastic means may be required if reflectors are badly soiled by chemical or other deposits. The reflector is aluminum. DO NOT use alkali cleaners since alkalies will dull reflector. Mild
D.Because of the high temperatures involved, periodically check and retighten heater terminal connections. This practice will help to avoid “hot terminals” and the resulting damage to wire insulation.
E.Because of the fire hazards resulting from a process malfunc- tion, the related safety control used in the system should be periodically checked to ensure its proper operation.
