User manual SEFELEC 5x Series 194 v1.06
19.6.3. Test time
Unlike a simple resistance measurement, the time that the current is being flowing for the
ground continuity measurement is important because of the ‘Safety’ function of the tested
connection.
Beyond the ohm value evaluation, it is mandatory to test the quality of the connection to the
ground potential (diameter of the wire, solders quality, screwing quality, ...). A manufacturing
fault of one of these connections may in certain circumstances give an immediate correct
ohm value but increasing quickly by heating causes by the high current value used for the
test: this high current can produce a break of the wire (wounded wire, which diameter be-
comes too small).
This is why some standards are requiring a minimum test time from 1 to 5 minutes for this
measurement. Other standards do not give any time indication, but it is advised to apply for
type test a minimum time of 1 minute and for series tests at least 10 seconds.
19.6.4. Precaution to be observed
The measured resistance values being very low (< 1 ohm), it is necessary to perform the meas-
urement in using the 4-wire method to avoid the measurement lead parasitic resistance (inter-
faces, adapters, ...) It is necessary to warrant this measurement principle when connecting the
measurement unit to the test points.
If specific connections have to be done, it is necessary to use correctly rated cables (at least
5 A/mm
2
) for the current and to connect voltage measurement cables as close as possible to the
measured points.
During the test time, it is advised not to move the probe to avoid breaking the current flowing
which will produce sparks. This can modify the real total test time and can alter the contact sur-
face of the specimen.
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