11
Instruction Leaflet
IL29C614F
Effective December 2011
Instructions for The Digitrip RMS 310 3-Pole and
4-Pole Trip Unit Installation and Operation with
K-Frame Series C Circuit Breakers
EATON CORPORATION
www.eaton.com
4.0 PRINCIPLE OF OPERATION
In open air at 40°C (104°F), an K Frame circuit breaker
with a Digitrip RMS 310 Trip Unit installed will carry cont-
inuously up to 400 amperes without exceeding a 50°C
(122°F) rise at the terminals. The calibration of the trip unit
is insensitive to ambient temperatures over a range of -20
to +55°C (-4 to 131°F) . However, the trip unit contains
thermal temperature protective circuitry that initiates a trip
operation for self-protection if the internal ambient temp-
erature at the printed circuit board (PCB) reaches approx-
imately 90°C (194°F). This may occur for open air temper-
atures above 40°C with circuit breaker currents near full
For ambient conditions above 40°C and where the maxi-
mum ampere rating plug has been installed, derating of
the circuit breaker frame should be considered to avoid
exceeding a safe terminal temperature operating range.
Consult Eaton for recommendations.
4.1 GENERAL
The Digitrip RMS 310 Trip Unit provides a tripping signal
to the flux transfer shunt trip when current and time
delay settings are exceeded. This is accomplished by
employing the Eaton custom designed integrated cir-
circuit Sµre™ chip, which includes a microcomputer
to perform its numeric and logic functions.
In the Digitrip RMS 310 Trip Unit, all required sensing
and tripping power to operate its
protection function
is
derived from the current sensors in the circuit breaker.
The secondary currents from these sensors provide the
correct input information for the protection functions, as
well as tripping power, when ever the circuit breaker is
carrying current. These current signals develop voltages
across the appropriate calibrating resistors.
The microcomputer, in cyclic fashion, repeatedly scans
the voltage values across each calibrating resistor and
enters these values into memory. These data are used
to calculate true RMS current values, which are then
repeatedly compared with the protection function settings
and other operating data stored in the memory. The soft-
ware program then determines whether to initiate protec-
tion functions, including tripping the breaker through the
flux transfer shunt trip device in the circuit breaker.
A green status light indicates the operational status of
the trip unit. If the load current through the circuit break-
er exceeds approximately 20% of the maximum current
rating of the trip unit, the status light will blink on and off
once each second. A blinking status light is an indication
of a properly functioning trip unit. If the status light is not
blinking, the current through the breaker may be less
than 20% of the maximum current rating of the trip unit.
If the current exceeds 20% and the status light is not
blinking, use the STK2 test kit to investigate (see section
6.1). IF THE STATUS LIGHT IS ON STEADY, IT INDI-
CATES A TRIP IS PENDING.
LACK OF ILLUMINATION OF THE STATUS LED
DOES NOT INDICATE THE TERMINALS OF THE
BREAKER ARE DEENERGIZED.
4.2 OVERLOAD TRIP
In accordance with standards requirements, the trip unit
initiates a trip of the circuit breaker within two hours for
an overload of 135 %, and will trip in less time for higher
overload currents.
A “Thermal Memory” effect prevents the breaker from
being re-energized immediately after an overload trip. A
“cooling off” period of up to 5 minutes is required, which
allows time for cabling to cool off.
4.3 SHORT DELAY/INSTANTANEOUS TRIP
For short circuit conditions that exceed the short delay
pick-up settings, the trip unit initiates a trip after a delay
prescribed by the I
2
t ramp function for trip units with cat-
alog number suffixes LS, LSE, LSP, and LSG. A flat
response time delay action is provided by trip units with
catalog number suffixes LSI, LSIE, and LSIG unless the
instantaneous (I) setting is selected.
4.4 GROUND FAULT PROTECTION
When selected, ground fault pick up and time delay set-
tings shown in Table
1-2
allow selective ground fault
coordination with other circuit protection devices.
5.0 PROTECTION SETTINGS
5.1 GENERAL
Prior to placing any circuit breaker in operation, each
trip unit protection setting must be set to the values
specified by the engineer responsible for the installation.
The available settings along with the effect of changing
the settings are illustrated in Figures
12-1
to
12-3
.
The installed rating plug establishes the maximum con-
tinuous current rating (I
n
) of the circuit breaker. Short
delay current settings are defined in multiples of I
n
.
!
CAUTION
load.
