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Volume 5—Motor Control and Protection CA08100006E—May 2013 www.eaton.com V5-T4-25
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4.3
Definite Purpose Contactors and Starters
Starters
Overload Relay
General
Overload relays are provided
to protect motors, motor
control apparatus and motor-
branch circuit conductors
against excessive heating
due to motor overloads and
failure to start. This definition
does not include: 1) motor
circuits over 600 volts, 2)
short-circuits, 3) ground faults
and 4) fire pump control.
(NEC Art. 430-31)
Time Current
Characteristics
The time-current
characteristics of an overload
relay is an expression of
performance which defines
its operating time at various
multiples of its current
setting. Tests are run at
Underwriters Laboratory (UL)
in accordance with NEMA
Standards and the NEC.
UL requires—
●
When tested at 100
percent of its current
rating, the overload relay
shall trip ultimately
●
When tested at 200
percent of its current
rating, the overload relay
shall trip in not more than 8
minutes
●
When tested at 600
percent of its current
rating, the overload relay
shall trip in not more than
10 or 20 seconds,
depending on the Class of
the relay or heater packs
“Current Rating” is defined
as the minimum current at
which the relay will trip. Per
NEC, an overload must
ultimately trip at 125% of FLA
(Full Load Amperes) current
(heater) setting for a 1.15
service factor motor and
115% FLA for a 1.0 service
factor motor.“Current
Setting” is defined as the
FLA of the motor and thus
the overload heater pack
setting.
Example: 600% of current
rating is defined as 750%
(600 x 1.25) of FLA current
(heater) setting for a 1.15
service factor motor. A 10
ampere heater setting must
trip in 20 seconds or less at
75 amperes motor current for
a Class 20 relay.
Overload Relay Setting
FLA Dial Adjustment—
For motors having a 1.15
service factor, rotate the FLA
adjustment dial to correspond
to the motor’s FLA rating.
Estimate the dial position
when the motor FLA falls
between two letter values as
shown in the example.
For motors having a 1.0
service factor, rotate the FLA
dial single-half position
counterclockwise (CCW).
Manual/Automatic Reset—
The overload relay is factory
set at M for manual reset
operation. For automatic
reset operation, turn the reset
adjustment dial to the A
position as shown in the
illustration.
Automatic reset is not
intended for two-wire control
devices.
Test for Trip Indication—
To test overload relay for trip
indication when in manual
reset, pull out the blue RESET
button. An orange flag will
appear indicating that the
device has tripped. Push
RESET button in to reset.
FLA Dial Adjustment Reset Adjustment Dial
Example of 12.0 FLA
setting for heater pack
number H2011B showing
position for 1.0 or 1.15
service factor motors.
Example of setting for manual
reset.
Replacement Overload with Connectors
AD
CB
1.0
Service
Factor
1.15
Service
Factor
A
M
Starter Size Overload Part Number
25 and 30A 10-7125
40 and 50A 10-7132
60A 10-7131