42.3.3 Available current more than

42.3.3 Available current more than 10.000 amperes42.3.3.1 For circuits intended to deliver more than 10,000 amperes, the current and power factor are to be determined in accordance with the requirements in 42.3.3.2 -42.3.3.8. Instrumentation used to measure test circuits of over 10,000 amperes is to comply with the requirements in 42.3.4.1 - 42.3.4.11.42.3.3.2 The rms symmetrical current is to be determined, with the supply terminals short-circuited by measuring the alternating-current component of the wave at an instant 1/2 cycle (on the basis of the test frequency timing wave) after the initiation of the short circuit. The current is to be calculated in accordance with Figure 7 in the Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis, ANSI/IEEE C37.09-1979(R1989).42 3 3.3 For a 3-phase test circuit, the rms symmetrical current is to be the average of the currents in the three phases. The rms symmetrical current in any one phase is not to be less than 90 percent of the required test current.42.3.3.4 The test circuit and its transients are to be such that:a) 3 cycles after initiation of the short circuit, the symmetrical alternating component of current will not be less than 90 percent of the symmetrical alternating component of current at the end of the first 1/2 cycle, orb) The symmetrical alternating component of current at the time at which the over current-protective device will interrupt the test circuit is at least 100 percent of the rating for which the device is being tested.In 3-phase circuits, the symmetrical alternating component of current of all three phases is to be averaged.42.3.3.5 The power factor is to be determined at an instant 1/2 cycle (on the basis of the test frequency timing wave) after the short circuit occurs. The total asymmetrical rms amperes are to be measured inaccordance with 42.3.3.2 and the ratio MA Or Mm is to be calculated as follows;