Scully ST-15C Series, Technical Manual

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1.1.1 Model Designations
The ST-15C Controller is available in 120VAC or 240VAC models, with or without control (bypass) switch.
Model suffix (E) = Explosion-proof Enclosure, (L) = Indicator Lights, (K) = Key Lockable Bypass Switch.
Model Description
ST-15C-120 EL
Single-Point Controller in Explosion-proof Enclosure with Indicator Lights, 120VAC
ST-15C-120 ELK Single-Point Controller in Explosion-proof Enclosure with Indicator Lights and Key-lockable
Bypass Switch, 120VAC
ST-15C-240 EL
Single-Point Controller in Explosion-proof Enclosure with Indicator Lights, 240VAC
ST-15C-240 ELK Single-Point Controller in Explosion-proof Enclosure with Indicator Lights and Key-lockable
Bypass Switch, 240VAC
1.1.2 Explosion Proof Enclosure
Suffix “E” in the model number indicates controller is in an explosion-proof enclosure suitable for hazardous
areas. Conduit holes are provided in the enclosure for electrical access. The installer must install EExd
cable glands (or conduit and seal fittings) according to local codes.
1.1.3 Indicator Lights
Suffix “L” in the model number indicates red and green indicator lights on the controller enclosure. These
lights indicate the following conditions:
GREEN RED Condition
ON OFF Sensor is dry and the circuit is functioning properly.
Controller output is in permissive state i.e. permit to load.
OFF ON Sensor is wet or faulty or no connection to sensor, or the circuit is
malfunctioning.
Controller output is in non-permissive state i.e. no permit to load.
OFF OFF No power to the unit.
1.1.4 Bypass Control Switch
Adding the suffix “K” to the model number adds a lockable two-position control switch to the enclosure. In
the ‘NORMAL’ position, the unit will operate normally, with “dry” sensors causing the output relay to become
energized (i.e. closed output contact). In the “BYPASS” position, power to the unit is switched “OFF” and
the normally open relay contacts are bypassed to permit emergency operation of the equipment, without
overfill protection.
For normal operation, this switch should always be set in the NORMAL position. The switch is enclosed in
lockable box to allow locking with a user provided padlock.
CAUTION: When in ‘BYPASS’ mode the controller and sensor are DISABLED and the system
does not provide overfill protection.
1.1.5 Indicator Light on Control Module
A L.E.D. light is mounted on the ST-15C module, inside the housing (see Figure 1). This LED flashes ON-
OFF when a dry, operational sensor is connected to the unit. This flashing LED indicates the Dynamic Self-
checking® or Dynacheck® operation of the control system. If the LED does not light under these
conditions, the ST-15C module could be defective.