090 Series Reference Manual
2/21/05
Digital Control Systems
Page: 12
Load Circuit Considerations
Triac Power Dissipation
The load is switched with a triac rated for 25 amps at 600 volts. When conducting, the triac
dissipates up to 1.4 Watts per Ampere of load current. At load currents above 1 amp the
mounting flange of the triac
must
be secured to a suitable heat sink. For moderate loads (less
than 8 to 10 amps) the triac can be screwed directly to painted metal. For higher loads direct
contact to bare metal is usually required and actual temperature at full load must be verified as
described below.
The power ECB is intended to be installed by screwing the triac’s mounting flange to a flat metal
surface with two # 6 screws. A 6” x 6” area of 18 Ga. cold rolled is usually adequate heat
sinking. Larger area will result in cooler operation for the same load current. Actual heat sink
temperature must be evaluated under full load conditions to ensure maximum operating
temperature of the triac is not exceeded.
Case temperature of the triac is measured at the exposed portion of the mounting flange
immediately adjacent to the mounting screw’s head. The maximum temperature at this point is
85
°
C. If the temperature at this point exceeds 85
°
C, more heat sink area must be provided or
the load current reduced.
Triac Fault Protection
The load circuit is not fused.
The triac used on the power ECBs is extremely rugged and can
usually endure load short-circuit current for long enough to trip a 15 to 20A branch circuit
breaker in most applications. In low source impedance applications where triac protection
under short circuit conditions is required, a fuse with an i2t rating of 260 Amps2 sec or less must
be installed in series with the load circuit.
Mechanical Mounting
The 090 series consists of a main ECB intended to mount behind a control panel, and one or two
smaller power ECBs.
The numeric LED digits and two buttons on the main ECB are the 090 series' user interface.
This board is intended to be mounted behind the end product's front panel with the LED display
showing through a cutout. Two additional cutouts below it allow actuation of the switches.
The power board contains the power and (optional) alarm relay connectors, and need not be
accessible to the user. It is intended to be mounted on an internal metal wall which also acts as
the triac’s heat sink.
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