Effective 8/2006
Page 14
I.L. 66A7534H04
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. 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.
NOTE:
The installed rating plug must match the CH Type-
V current sensors which establish the maximum continu-
ous 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 appropri-
ate 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 box.
4.2 Long Delay Current Setting
There are eight available “Long Delay Settings” as illus-
trated in Figure 4.1. Each setting, called (
I
r), is expressed
as a multiple (ranging from .4 to 1) of the current (
I
n). The
nominal current pickup value is 110% of the setting.
NOTE:
(
I
r) is also the basis for the “Short Delay Current
Setting”
(see Section 4.4).
Figure 4.1 Long Delay Current Settings
4.3 Long Delay Time Setting
There are eight 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,” trip units also have a “Long Time Memory” (LTM)
function, which protects load circuits from the effects of
repeated overload conditions. If a circuit 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.)
