KS 3-2010
Page 15
Figure 6
Non-Fused Switch Individual Pole Resistance Test Set-Up
6.4.1 Purpose
To assess the electrical integrity of internal connections and contacts in a switch. This can be done by
conducting a millivolt drop test across the line and load terminals of each pole with the switch contacts
closed.
The millivolt drop (resistance) of a switch pole can vary significantly because of inherent variability in the
extremely low resistance of the electrical contacts and connectors. Such variations do not necessarily
predict unacceptable performance and should not be used as the sole criteria for determination of
acceptability.
6.4.2 Equipment
6.4.2.1 This test should be conducted using a 24 volt, or less, direct current power supply capable of
supplying the rated current of the switch. For switch rated higher than 500 amperes, the power
supply should be capable of delivering no less than 500 amperes.
6.4.2.2 If the above equipment is not available for field tests, a Digital Low Resistance Ohmmeter
(DLRO), or 4-point tester, capable of 10 to 100 amperes (dc) may be used.
NOTE—Use of a multimeter or low current ohmmeter in place of the power supply will not provide an accurate or reliable
measurement of millivolt drop and should not be used.
CAUTION—Do not exceed the current rating of the fuse where the fuse cannot be isolated from the test
circuit.
6.4.3 Procedure
WARNING—Follow all safety procedures described in Section 2.
6.4.3.1 After being properly isolated, remove the switch from the enclosure. In cases where the switch
can be safely isolated/disconnected as installed, the test may be performed with the switch in
its equipment.
© Copyright 2010 by the National Electrical Manufacturers Association.
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