© 2016 Littelfuse Protection Relays & Controls

www.littelfuse.com/

Rev: 1-A-062716

Protection Relays

Current Monitoring Relays and Transducers

www.littelfuse.com/ecsw

ECSW SERIES

trip delay, the relay transfers to fault condition state. If the

current returns to normal levels (inside the window) during the

trip delay, the red LED goes OFF, the trip delay is reset, and the

output remains in the normal condition.

Reset: Remove input voltage or open latch switch. If zero

current detection is selected, the unit will reset as soon as zero

current is detected.

Operation With Zero Current Detection Enabled: If the

current decreases to zero within the trip delay period, then

zero current is viewed as an acceptable current level. The unit’s

output remains in its normal operating state. This allows the

monitored load to cycle ON and OFF without nuisance tripping

the ECSW. Zero current is defined as current flow of less than

250 milliamp-turns.

Note: When zero current detect is selected, the latching

operation of switch SW2 is canceled; the output will not latch

after a fault trip.

Notes on Operation

1. There is no hysteresis on the trip points. The overcurrent

and undercurrent trip points should be adjusted to provide

adequate protection against short cycling.

2. If the upper setpoint is set below the lower setpoint, both

red LED’s will glow indicating a setting error.

3. If zero current detection is selected (SW2 ON), and the

system is wired to disconnect the monitored load, the

system may short cycle. After the unit trips, the load de-

energizes, and zero current is detected. The ECSW resets,

and the load energizes again immediately and may be

short cycled.

4. The sensing delay on start up only occurs when input voltage

is applied. When zero current detection is selected, the trip

delay must be longer than the duration of the inrush current

or the unit will trip on the inrush current.

Typical Pump or Fan Protection Circuit Operation

Window Current Sensing: With the ECSW connected as

shown in the diagram, a load may be monitored and controlled

for over and undercurrent. The ECSW Series’ on board CT (CS)

may be placed on the line or load side of the contactor. The

ECSW selection switches are set for zero current sensing (see

Selector Switch SW2) and the output selection is normally de-

energized (see Selector Switch SW3). The input voltage (V) is

applied to the ECSW continually. As the control switch (FSW) is

closed, the input voltage (V) is applied to the motor contactor

coil (MCC), and the motor (M) energizes. As long as the current

remains below the overcurrent and above the undercurrent

trip points, the ECSW’s output contacts remain de-energized.

If the load current should rise above or fall below a trip point,

for the full trip delay, the normally open (NO) contact will

close, energizing the control relay (CR) coil. The CR normally

closed contact (CR1) opens and the MCC de-energizes and

CR latches on through its normally open contacts (CR2). Reset

is accomplished by momentarily opening the normally closed

reset switch (RSW).

Note: If the current falls to zero within the trip delay, the ECSW

remains de-energized. The sensing delay on startup occurs

when input voltage is applied therefore trip delay must be longer

than the duration of the motor’s inrush current. The external

latching relay CR2 is required in this system to prevent rapid

cycling. A timer can be added to provide an automatic reset.

Selector Switch

Not Used

Latched

Zero I

Output - Normally Energized

ON

OFF

SW1

SW2

SW3

Mode Selection Switches

SW1 = Latched or Auto reset selector

OFF - Automatic reset after a fault

ON - Output relay latches after a fault trips the unit

SW2 = Zero current detection (below 250 mA)

OFF - Zero current detection disabled

ON - Zero current detection enabled

SW3 = Output during normal operation

OFF - Output relay de-energized

ON - Output relay energized