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SECTIO N 1 5-EC Trip Device (Cont.)

1 5.1

SERIES OVERCURRENT TRIPPING

DEVICE EC-2A

The Type EC-2A overcurrent tripping device is available in

three forms:

1 . Dual overcurrent trip, with long-time delay and high-set in-

stantaneous tripping.

2.  Low-set instantaneous tripping.
3.  High-set instantaneous tripping.
The  dual  trip  has  adjustable  long-time  and  instantaneous

pick-up settings and adjustable time settings. Both forms of in

stantaneous trip have adjustable pick-up settings.

ADJ USTMENT NOTE

Before attempting any checks or adjustments on breaker with

EC trip devices, the breaker mechanism and trip latch should be

checked  to  assure  their  proper  functioning  so  that  the  breaker
trip  shaft  is  free  of  high  friction  loads.  The  trip  latch  of  the
breaker  should  also  be  checked  for  proper  trip  latch  engage

ment. See Section 7. 1 5

Refer to Fig. 1 2 1 for the discussions given below.

1 5. 1 .1

LONG TIME-DELAY AND HIGH-SET

INSTANTANEOUS TRIPPING

By means of the adjustment knob (3), which can be manipu

lated by hand, the current pick-up point can be varied from 80

to 1 60 percent of the series coil rating. The indicator and a cal

ibration  plate  (2)  on  the  front  of  the  case  provide  a  means  of
indicating the pick-up point setting in terms of percentage of coil
rating. The calibration  plate  is indexed at percentage settings of
80,  1 00,  1 20,  1 40, and  1 60.

As in the case of the EC-1 over-current trip, the long-time de

lay tripping feature can be supplied with any one of three

time-current characteristics which correspond to the NEMA
standards maximum, intermediate and minimum long-time delay
operating bands. These are identified as 1 A, 1 B and 1 C char

acteristics, respectively. Approximate tripping time

for

each

these, in the same order are 30, 1 5, and 5 seconds at 600 per
cent of the pick-up value of current. (See time-current charac
teristic curves).

The tripping time may be varied within the limits shown on the

characteristic  curves  by  turning  the  time  adjustment  screw  (4).
Turning  in  a  clockwise  direction  increases  the  tripping  time;
counterclockwise  motion  decreases  it.  The  dashpot  arm  (8)  is

indexed at four points, MIN-1 /3-2/3-MAX, as indicated in Fig.

1 22.

When the index mark on the connecting link {9) lines up

with a mark on the dashpot arm, the approximate tripping time
as shown by the characteristic curve is indicated. The 1 A and

1 B characteristic devices are shipped with this setting at the 2/3
mark and the 1 C characteristic at the 1 /3 mark. The standard

characteristic curves are plotted at these same settings.

Time values are inversely proportional to the effective length

of the dashpot  arm.  Therefore, the  linkage setting that gives the
shortest  time  value  is the one at  which  dimension  "A",  Fig. 1 2 1 ,
is greatest.  The time adjustment screw (4) may be turned by in

serting  a  Phillips  head  screwdriver through the hole in the front
of  the  case.  If  it  is  desired  to  relate  the  linkage  setting  to  the
index  marks  on  the  linkage  it  will  be  necessary to  remove the

case. This may be done by removing the two mounting screws,
one on each side of the case, which may be taken off without
disturbing the trip unit itself.

1 5.1 .2

INSTANTANEOUS LOW-SET TRIPPING

The low-set instantaneous pick-up point may be varied by the

adjustment knob (3). The calibration in tflis case usually ranges

from 80 percent to 250 percent of the series coil rating, with the
calibration plate indexed at values of 80,

1 00,

1 50,

200,

and 250

percent of the rating.

1 5.1 .3

INSTANTANEOUS HIGH-SET TRIPPING

The high-set instantaneous pick-up value may have one of

the following three ranges: 4 to 9 times coil rating; 6 to 1 2 times

coil rating or 9 to 1 5 time coil rating. The pick-up setting may be

varied by turning the instantaneous pick-up adjusting screw

(1 2).

Three calibration marks ( 1 5) will appear on the operating arm

( 1 4) and the value of these calibration marks will be indicated

by stampings on the arm as follows: (4X - 6.5X - 9X) or (6X -
9X - 1 2X) or (9X - 1 2X - 1 5X).

At the factory, the pick-up point has been set at the name

plate value of the instantaneous trip current.  (Usually expressed
in times the ampere  rating of the trip coil). The variation in pick
up  setting  is  accomplished  by  varying  the  tensile  force  on  the
instantaneous spring  (5).  Turning the adjustment screw changes

the position of the movable nut (1 1 ) on the screw. The spring is
anchored to this movable nut so that when the position of the

nut is changed, there is a correspondin.g change in the spring
load. As the spring is tightened, the pick-up point is increased.

The top edge of the mov

ble nut (1 1 ) serves as an index

pointer and should be lined up with the center of the desired cal
ibration mark (1 5) to obtain the proper instantaneous trip setting.

The trip screw (6) on the end of the armature (7) should be

set so that it does not contact the trip paddle on the trip shaft

until the air gap between armature and pole piece is reduced to
3/32 in. or less, measured at the rivet in the pole piece. Also,

the armature must have a minimum of 1 /32 in. of travel beyond
the point in its motion at which the breaker is tripped.

Replacement of the EC-2A device

accomplished by the

same procedure described for the EC-1 series trip device; how
ever, in some cases, when replacing an EC-1 device with an