Eaton Digitrip 520 Instructional Leaflet page 12

Instructional Leaflet IL70C1037H05
Effective October 2009
m CAUTION
IF THE SENSOR CONNECTIONS ARE INCORRECT, A NUISANCE TRIP
MAY OCCUR. ALWAYS OBSERVE THE POLARITY MARKINGS ON THE
INSTALLATION DRAWINGS. TO ENSURE CORRECT GROUND FAULT
EQUIPMENT PERFORMANCE, CONDUCT FIELD TESTS TO COMPLY WITH
NEC REQUIREMENTS UNDER ARTICLE 230-95(C).
Source ground sensing
Depending upon the installation requirements, alternate ground
fault sensing schemes may be dictated (see Figurt 11 and
Figurt 12). The ground return method is usually applied when
ground fault protection is desired only on the main circuit breaker
in a simple radial system. This method is also applicable to double-
ended systems where a midpoint grounding electrode is employed.
For this mode of sensing, a single current sensor mounted on
the equipment-bonding jumper directly measures the total ground
current flowing in the grounding electrode conductor and all other
equipment-grounding conductors.
The settings shown in Tablt 3 will apply when the neutral
sensor is not the same as the frame rating in a ground return
sensing scheme.
Tablt 4. GrNund (Earoh) Faulo Currtno Stooings
Ground Fault Current Settings (Amperes)
Installed Sensor and Rating Plug (Amperes) I
200
250
300
400
600
630
800
1000
1200
1250
1600
2000
2500
3000
3200
4000
c
5000
c
6000
6300
c
Tolerance on settings are ±10% of values shown.
a
On models 520 LSIG, 520M, and 520MC LSIG, the shaded values are set to a maximum trip value of 1200A for NEC.
b
See page 17.
c
12
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a
0.25
n
50
63
75
100
150
158
200
250
300
312
400
500
625
750
800
1000
1250
b
1500
b
1575
Digitrip models 520, 520i; and 520M, 520Mi,
520MC, 520MCi trip units for use only in
Magnum and Magnum DS circuit breakers
Zero sequence sensing
Zero sequence sensing, also referred to as vectorial summation
(see Figurt 13), is applicable to mains, feeders, and special
schemes involving zone protection. Zero sequence current
transformers (5.06 x 15.37 in. [128 x 390 mm] rectangular inside
dimensions) are available with 100:1 and 1000:1 ratios (styles
9253C07G01, G11).
Multiple source/multiple ground
A multiple source/multiple ground scheme is shown in Figurt 14.
In this figure, a ground fault is shown that has two possible return
paths, via the neutral, back to its source. The three neutral sensors
are interconnected to sense and detect both ground fault and
neutral currents.
Contact Eaton for more details on this scheme.
Ground fault settings
The adjustment of the ground fault functional settings (FLAT
response or I t) is discussed in Section 4. The effect of these
2
settings is illustrated in the ground fault time-current curve
referenced in Section 9. Applicable residual ground fault pickup
settings and current values are given in Tablt 4, as well as in the
ground time-current curve.
0.30 0.35 0.40
60 70 80
75 88 100
90 105 120
120 140 160
180 210 240
189 221 252
240 280 320
300 350 400
360 420 480
375 438 500
480 560 640
600 700 800
750 875 1000
900 1050 1200
960 1120 1200
1200 1400 1600
b b
1500 1750 2000
b b b
1800 2100 2400
b b b
1890 2205 2520
0.50 0.60 0.75
100 120 150
125 150 188
150 180 225
200 240 300
300 360 450
315 378 473
400 480 600
500 600 750
600 720 900
625 750 938
800 960 1200
1000 1200 1500
b
1250 1500 1875
1500 1800 2250
b b b
1600 1920 2400
b b b
2000 2400 3000
b b b
2500 3000 3750
b b b
3000 3600 4500
b b b
3150 3780 4725
1.0
200
250
300
400
600
630
800
1000
1200
1250
1600
b
2000
b
2500
3000
b
3200
b
4000
b
5000
b
6000
b
6300