Regardless, what do the results even mean? Since I was one of 2 beaker applications engineers for a major breaker manufacturer and no where did we have a procedure for measuring breaker contact resistance as an acceptable test for breaker "health." As such where are these contact resistance test procedures coming from? It isc not a legitimately recognized test by the manufacturer that I worked for.
Resistance=heating. Also, contact resistance will in fact change with each opening and closing of the breaker. The breakers tested with 24vdc does in no way compare to breakers commonly operationing at 120, 208, 240, and 480v to 600v with often times hundreds of amps.
The test as you suggest is not a test that a manufacturer recognizes. Field testing procedures are as included is NEMA AB4. As far as a microhmeter is concerned it has never been applicable in any breaker testing procedures even in the breaker testing procedures as commonly conducted in our warranty returns facility.
My objective is to stay focused of accepted industrial/commercial breaker testing procedures. Any contact resistance results I would consider as a symptom and not something that would determine to be a reason for rejection as there are no breaker contact resistance standards.
Um, I was directly quoting from NEMA AB4 (They say DLRO in leiu of microohmeter but DLRO is a brand name for Meggers microhmeter), but as stated earlier contact resistance is just one of many tests to be used to determine condition. Same test is also part of the NETA/ANSI standards.
6.4 INDIVIDUAL POLE RESISTANCE TEST (MILLIVOLT DROP)
See Figure 7 and Figure 8 for typical test set up.
NOTE?The circuit breaker should be removed from the equipment for this test. In cases where the circuit breaker can be safely
isolated as installed, the test may be performed with the circuit breaker in its equipment.
6.4.1 Purpose
To assess the electrical integrity of internal connections and contacts in a circuit breaker. This can be done
by conducting a millivolt drop test across the line and load terminals of each pole with the circuit breaker
contacts closed.
The millivolt drop (resistance) of a circuit breaker pole can vary significantly due to 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 (See 6.4.5).
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 circuit breaker. For circuit breakers 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.
6.4.3 Procedure
6.4.3.1 After being properly isolated, remove the breaker from the enclosure. In cases where the circuit
breaker can be safely isolated/disconnected as installed, the test may be performed with the circuit breaker
in its equipment.
6.4.4 Test
NOTE?If the circuit breaker is equipped with an under-voltage trip release, energize the trip release to allow proper operation of the
circuit breaker (See 7.3 for proper procedures).
6.4.4.1 The test is performed as follows:
6.4.4.1.1 Apply test current across a pole equal to the breaker rating (or 500 Amperes minimum for
breakers rated in excess of 500 Amperes). Record the millivolt drop and the test current. Do not maintain
current for more than 1 minute. If this equipment is not available, use the following test.
6.4.4.1.2 Apply test current across a pole of 10 Amperes, or the Ampere rating of the breaker, for breakers
rated less than 100 Amperes. For breakers rated more than 100 Amperes, apply a test current across a
pole of 100 Amperes. Record the millivolt drop and the test current, or resistance. Do not maintain current
for more than 1 minute.
6.4.4.1.3 De-energize the test circuit. Manually operate the breaker to the OFF and then ON positions.
6.4.4.1.4 Repeat steps 6.4.4.1.1 and 6.4.4.1.2 for a total of three readings on the pole being tested.
6.4.4.1.5 Repeat steps 6.4.4.1.1 through 6.4.4.1.3 for each of the remaining poles of the circuit breaker.
6.4.5 Results
The results of test will vary according to the breaker frame type, ampere rating, and manufacturer. The
manufacturer should be consulted to determine the maximum allowable voltage drop. If the average test
values of any pole of the breaker exceed the maximum allowable drop, the circuit breaker may have
reached the end of life and additional tests may have to be conducted.
NOTE?Inconsistent readings could be the result of oxide films or foreign material on the contact surfaces, depending on the service
history of the breaker. If high millivolt or high resistance readings are detected, it may be advisable to do tests in section 6.6, which
may help clean conta