23
Instructional Leaflet
IL70C1037H05
Effective October 2009
Digitrip models 520, 520i; and 520M, 520Mi,
520MC, 520MCi trip units for use only in
Magnum and Magnum DS circuit breakers
eaton corporation
www.eaton.com
Figurt 32. LNng Timt MtmNry (LTM) Jumptr
The action of the LTM must be considered when performing
multiple long delay time tests (see Section 5).
ShNro dtlay currtno stooing
There are eight available short delay current settings, as illustrated
in
Figurt 31
. Seven settings are in the range from 2–10 times (I
r
).
(Remember: (I
r
) is the long delay current setting.) The maximum
value M1 is based on the ampere rating of the circuit breaker and is
listed in Note 4 of
Tablt 1
.
Figurt 33. ShNro Dtlay Currtno Stooings
ShNro dtlay oimt stooing
As illustrated in
Figurt 34
, there are two different short delay
response curve shapes: fixed time (FLAT) and I
2
t.
The shape selected depends on the type of selective coordination
chosen. The I
2
t response curve will provide a longer time delay for
current below 8 x I
r
than will the FLAT response curve.
Test Kit
Digiorip Ttso Kio PNro
Test Kit
Notch
Connector
(Storage)
LTM Active
Connector
(Bridging)
LTM Inactive
(Also Recommended
Position for Field Testing)
Short Delay Setting
2 x
l
r
Available Settings
2.0, 2.5, 3.0. 4.0, 5.0, 6.0, 8.0, 10.0, M1
In Multiples of
Long Delay Setting (
l
r
)
M1 Value is Specified on Rating Plug
LNng dtlay oimt stooing
There are eight available long delay time settings, as illustrated in
Figurt 31
, ranging from 2–24 seconds. These settings are the total
clearing times when the current value equals six times (I
r
).
Figurt 31. LNng Dtlay Timt Stooings
Notse:
N
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 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. 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
Figurt 32
) 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.)
Long Delay Time
2 Seconds at 6 x
l
r
Available
Settings
2, 4, 7, 10,
12, 15, 20, 24
Seconds at
6 Times
Long Delay
Setting (
l
r
)
6 x
l
r
