Manual Gossen Metrawatt Profitest Intro (page 25 of 62) (English)

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GMC-I Messtechnik GmbH 25

8 Testing of Breaking Requirements for

Overcurrent Protective Devices,

Measurement of Loop Impedance and Determi-

nation of Short-Circuit Current (functions ZL-PE

and IK)

Testing of overcurrent protective devices includes visual inspec-

tion and measurement. Use the PROFITEST INTRO to perform mea-

surements.

Measuring Method

Loop impedance ZL-PE is measured and short-circuit current IK is

ascertained in order to determine if the breaking requirements for

protective devices have been fulfilled.

Loop impedance is the resistance within the current loop (utility

station – phase conductor – protective conductor) when a short-

circuit to an exposed conductive part occurs (conductive connec-

tion between phase conductor and protective conductor). Short-

circuit current magnitude is determined by the loop impedance

value. Short-circuit current IK may not fall below a predetermined

value set forth by DIN VDE 0100, so that reliable breaking of the

protective device (fuse, automatic circuit breaker) is assured.

Thus the measured loop impedance value must be less than the

maximum allowable value.

Tables containing allowable display values for loop impedance

and minimum short-circuit current display values for ampere rat-

ings for various fuses and circuit breakers can be found in the

help texts and in section 19 beginning on page 54. Maximum

device error in accordance with VDE 0413 has been taken into

consideration in these tables. See also section 8.2.

In order to measure loop impedance ZL-PE, the instrument uses a

test current of 3.7 A to 7 A (60 to 550 V) depending on line volt-

age and line frequency. The test has a duration of max. 1200 ms

at 16 Hz.

If dangerous touch voltage occurs during measurement (> 50 V),

safety shut-down occurs.

The test instrument calculates short-circuit current IK based on

measured loop impedance ZL-PE and line voltage. Short-circuit

current calculation is made with reference to nominal line voltage

for line voltages which lie within the nominal ranges for 120 V,

230 V and 400 V systems. If line voltage does not lie within these

nominal ranges, the instrument calculates short-circuit current IK

based upon prevailing line voltage and measured loop impedance

ZL-PE.

Measuring Method with Suppression of RCD Tripping

The PROFITEST INTRO provides users with the opportunity of mea-

suring loop impedance within systems which are equipped with

RCCBs.

The test instrument

generates a direct

current to this end,

which saturates the

RCCB’s magnetic

circuit.

The test instrument

then superimposes

a measuring cur-

rent which only

demonstrates half-

waves of like polar-

ity. The RCCB is no

longer capable of

detecting this mea-

suring current, and

is consequently not tripped during measurement.

Select the Measuring Function

Connection:

Schuko/3-pole

(country specific)

Connection: 2-pole

Note

Loop impedance should be measured for each electrical

circuit at the farthest point, in order to ascertain maxi-

mum loop impedance for the system.

Note

Bias Magnetization

Suppression of RCD tripping by means of bias magneti-

zation with direct current is only possible via a country-

specific measuring adapter, e.g. PRO-Schuko measuring

adapter (Z503K) or the KS-PROFITEST INTRO (Z503L)

for 3-pole measurement (neutral conductor required).

Note

Observe national regulations, e.g. the necessity of con-

ducting measurements without regard for RCCBs in Aus-

tria.

3-Phase Connections

Measurement of loop impedance to earth must be performed at

all three phase conductors (L1, L2, and L3) for the testing of over-

current protective devices at three phase outlets.

Start

t1 t3

Measuring

Operation

RCD Disabled!

IF/mA

Suppression of RCCB tripping for RCCBs which are

sensitive to pulsating current

L-PE

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Gossen Metrawatt Profitest Intro Manual

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