Protection Settings; General; Long Delay Current Setting; Long Delay Time Setting - Eaton Cutler-Hammer Digitrip 520M Instructions Manual

I.L. 70C1037H02

4.0 PROTECTION SETTINGS

4.1 General

Before placing any circuit breaker in operation, set each
trip unit protection setting to the values specified by the
engineer responsible for the installation. The number of
settings that must be made is determined by the type of
protection supplied by each unit, as illustrated in Figures
3.2 through 3.9. Each setting is made by turning a rotary
switch, using a small screwdriver. The selected setting for
each adjustment appears on the trip unit label.
The installed rating plug must match the current sensors
which establish the maximum continuous current rating of
the circuit breaker ( I n). Instantaneous and ground current
settings are defined in multiples of ( I n).
To illustrate the effect of each protection curve setting,
simulated time-current curves are pictured on the face of
the trip unit. Each rotary switch is located nearest the
portion of the simulated time-current curve that it controls.
Should an automatic trip occur (as a result of the current
exceeding the pre-selected value), the LED in the appro-
priate segment of the simulated time-current curve will
light red, indicating the reason for the trip.
The available settings, along with the effects of changing
the settings, are given in Figures 4.1 through 4.8. Sample
settings are represented in boxes ( 2 ).

4.2 Long Delay Current Setting

There are 8 available Long Delay Settings, as illustrated
in Figure 4.1. Each setting, called ( I r), is expressed as a
multiple (ranging from .4 to 1) of the current ( I n).
NOTE: ( I r) is also the basis for the Short Delay Current
Setting (see Section 4.4).
Figure 4.1 Long Delay Current Settings
Effective 8/13/99
Courtesy of NationalSwitchgear.com

4.3 Long Delay Time Setting

There are 8 available Long Delay Time Settings, as
illustrated in Figure 4.2, ranging from 2 to 24 seconds.
These settings are the total clearing times when the
current value equals 6 times ( I r).
Figure 4.2 Long Delay Time Settings
NOTE: In addition to the standard Long Delay Protection
Element, the DT20 family of trip units also has a Long
Time Memory (LTM) function, which protects load circuits
from the effects of repeated overload conditions. If a
breaker is reclosed soon after a Long Delay Trip, and the
current again exceeds the Long Delay Setting, ( I r), the
LTM automatically reduces the time to trip to allow for the
fact that the load circuit temperature is already higher
than normal because of the prior overload condition. Each
time the overload condition is repeated, the LTM causes
the breaker to trip in a progressively shorter time. When
the load current returns to normal, the LTM begins to
reset; after about 10 minutes it will have reset fully, so the
next Long Delay trip time will again correspond to the
Setting value.
NOTE: In certain applications, it may be desirable to
disable the LTM function. Open the test port located at the
lower left-hand front of the trip unit and use small, long-
nose pliers to move the LTM jumper inside the test port
(see Figure 4.3) to its Inactive position. (The LTM function
can be enabled again at any time by moving the LTM
jumper back to its original Active position.)
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