Earth-Leakage Circuit Breakers: Thermal Magnetic and Earth-Leakage Protections
Introduction
Earth-leakage circuit breakers provide the following protection functions:
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Long time protection against overload with an adjustable pickup Ir, and a non-adjustable time delay tr.
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Short-time protection against short-circuits, with an adjustable pickup Isd, and a non-adjustable time delay tsd.
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Instantaneous protection against short-circuits, with a fixed pickup Ii.
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Neutral protection against overload and short-circuits.
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Earth-leakage protection, against low intensity residual current, with an adjustable pickup IΔn, and an adjustable time delay Δt.
The following figures show the tripping curves:
Trip Unit Description
The adjustment dials and indications are on the front face of the trip unit or are accessible after opening protective covers.
A Long-time protection pickup setting (Ir)
B Earth-leakage protection pickup setting (IΔn)
C Earth-leakage protection time delay setting (Δt)
D Seal for setting cover
E Switch to isolate the device during dielectric tests
F Tripping curve and instantaneous pickup (Ii)
G Short-time protection pickup setting (Isd)
H Test port
I Indication LEDs
J Neutral protection setting (4P device only)
Indication LEDs
Indication LEDs on the front of the trip unit indicate its operational state.
|
Indication LED |
Description |
|---|---|
|
Green READY LED |
Blinks slowly when the standard protection functions of the electronic trip unit are operational. |
|
Orange overload pre-alarm LED |
Steady on when I > 90% Ir. |
|
Red overload alarm LED |
Steady on when I > 105% Ir |
Setting the Long Time Protection
The long time protection pickup Ir is set by using an adjustment dial.
The long time protection tripping range is 1.05–1.20 Ir according to standard IEC/EN 60947-2.
|
Rating In (A) |
Preset values of Ir (A) depending on the rating In and the dial position |
||||||||
|---|---|---|---|---|---|---|---|---|---|
|
25 |
10 |
11 |
12 |
14 |
16 |
18 |
20 |
22 |
25 |
|
50 |
20 |
22 |
25 |
28 |
32 |
36 |
40 |
45 |
50 |
|
100 |
40 |
45 |
50 |
56 |
63 |
70 |
80 |
90 |
100 |
|
160 |
63 |
70 |
80 |
90 |
100 |
115 |
130 |
145 |
160 |
The time delay tr for long time protection cannot be adjusted.
The following table shows the value of the time delay tr for long time protection (in seconds) according to the overload current (in multiples of Ir).
|
at 1.5 Ir |
at 6 Ir |
at 7.2 Ir |
|---|---|---|
|
tr = 200 s |
tr = 8 s |
tr = 5 s |
The accuracy range is -20%/+0%.
Thermal Memory
The trip unit incorporates the thermal memory function which ensures that the conductors are cooled even after tripping. Cooling lasts for 20 minutes before or after tripping.
Setting the Short-Time Protection
The short-time protection pickup Isd is set by using an adjustment dial.
The setting value is expressed in multiples of Ir.
|
Step |
Action |
|---|---|
|
1 |
Set the long time protection first: the setting pickup is Ir. |
|
2 |
Turn the Isd adjustment dial to the value required. The Isd value is adjustable from 1.5 Ir to 10 Ir. |
|
3 |
Isd = Isd setting x Ir. |
The accuracy range is +/-15%.
The time delay tsd for short-time protection cannot be adjusted:
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Non-tripping time: 20 ms
-
Maximum breaking time: 80 ms
Example of Setting the Short-Time Protection
Setting the short-time protection pickup Isd to 500 A on an earth-leakage circuit breaker rated (In) 160 A (see diagram below).
|
Step |
Action |
|
|---|---|---|
|
1 |
The setting pickup Ir for long time protection is equal to 100 A. |
 |
|
2 |
Setting calculation: Isd/Ir = 500/100 = 5 Position the Isd adjustment dial on setting 5. |
 |
|
3 |
Isd is set to 5 x 100 A (= 500 A). |
 |
Setting the Instantaneous Protection
The pickup Ii and time delay for instantaneous protection cannot be adjusted.
The following table shows the value of the pickup Ii (in amperes) and time delay (in milliseconds) for instantaneous protection according to the rating In:
|
Rating In (A) |
25 |
50 |
100 |
160 |
|---|---|---|---|---|
|
Pickup Ii (A) |
375 |
750 |
1500 |
2000 |
|
Non-tripping time (ms) |
10 |
10 |
10 |
5 |
The accuracy range of pickup is +/-15%.
The maximum breaking time is 50 ms for I > 1.5 Ii
Setting the Neutral Protection (4P Only)
The neutral selection dial gives a choice of two or three values for the neutral long time and short-time protection pickups.
The following table shows the values of the pickup for neutral long time protection (in multiples of Ir) and neutral short-time protection (in multiples of Isd) according to the dial position:
|
Rating In (A) |
Dial |
Setting |
Long-time setting value |
Short-time setting value |
|---|---|---|---|---|
|
25–50 |
OFF (4P 3D) |
– |
– |
|
|
100% (4P 4D) |
Ir |
Isd |
||
|
100–160 |
OFF (4P 3D) |
– |
– |
|
|
50% (4P 3D + N/2) |
Ir/2 |
Isd/2 |
||
|
100% (4P 4D) |
Ir |
Isd |
The time delay for the neutral long time protection and short-time protection is the same as that for the phases.
Operating Principle of Earth-Leakage Protection
Earth-leakage protection is definite time. The earth-leakage protection threshold IΔn sets the level of earth-leakage at which the circuit breaker trips when reaching the earth-leakage protection time delay Δt.
Setting the Earth-Leakage Protection
The earth-leakage protection IΔn is set by using one adjustment dial.
The following table shows the value of the pickup IΔn for earth-leakage protection according to the type defined in IEC/EN 60947-2, Annex B standard:
|
Earth-leakage type |
Pickup IΔn |
||||||
|---|---|---|---|---|---|---|---|
|
A(1) |
30 mA |
100 mA |
300 mA |
500 mA |
1 A |
– |
– |
|
AC(2) |
30 mA |
100 mA |
300 mA |
500 mA |
1 A |
3 A |
5 A |
|
(1) Residual current circuit breakers which provide additional protection to AC type in that they are sensitive to AC currents and pulsating DC currents. Tripping is ensured for sinusoidal, alternating residual currents as well as for pulsed DC residual currents, whether suddenly applied or slowly arising. (2) Residual current circuit breakers sensitive to AC currents and suitable for most domestic and commercial applications. Tripping is ensured for sinusoidal, alternating currents, whether suddenly applied or slowly arising. |
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Setting the Earth-Leakage Protection Time Delay
The time delay of the earth-leakage protection is set by using one adjustment dial.
When IΔn is set to 30 mA, the time delay has a fixed value of Δt = 0 s (instantaneous tripping).
When IΔn is set above 30 mA, the time delay Δt can be adjusted to the following values:
-
0 ms
-
60 ms
-
150 ms
-
500 ms
-
1 second
Testing the Earth-Leakage Protection
The earth-leakage protection must be tested regularly by using the test button (T). Pressing the test button simulates a real leakage current passing through the toroid, and the device trips.
 CAUTION |
|---|
|
HAZARD OF NUISANCE TRIPPING
Circuit breaker tests must only be done by qualified electrical
personnel.
Failure to follow these instructions can result in injury or equipment damage.
|
When testing the earth-leakage protection function, take precautions against:
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Disrupting operations
-
Activating inappropriate alarms
-
Triggering unwanted actions
Follow these steps to test the earth-leakage protection of an earth-leakage circuit breaker (for example, with a toggle handle).
|
Step |
Action |
|
|---|---|---|
|
1 |
Energize the earth-leakage circuit breaker: 200 Vac ≤ VL-L ≤ 440 Vac. |
– |
|
2 |
Push the toggle handle from the O (OFF) position to the I (ON) position. The circuit breaker is closed. |
|
|
3 |
Press the test button T: the earth-leakage circuit breaker trips and the earth-leakage trip indication lights up. NOTE: If the earth-leakage circuit breaker does not trip:
|
|
|
4 |
Push the toggle handle from the The earth-leakage trip indication:
|
|
|
5 |
Push the toggle handle from the O (OFF) position to the I (ON) position. The earth-leakage trip indication turns off (if the earth-leakage circuit breaker is energized upstream). The circuit breaker is closed. |
|
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Every three months in case of absence of local regulation.
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Once a month for devices in corrosive, dusty, or harsh environment.