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| periodically, or following an operation under severe fault conditions, and their results used to determine the extent of maintenance required. Full maintenance schedules based on regular time periods can thus be extended considerably. |

| Contacts are tested by taking resistance measurements across the terminals of each pole of a breaker. Oil tests determine the condition of the insulation generally. The working condition of the operating mechanisms can be determined by recording the time and smoothness of the opening and closing of the lift rod. All these tests can be accomplished in a relatively short time, perhaps even less than an hour, by a small crew, without undertaking the long and tedious process of draining oil from the tanks so that they can be dropped and then the equally long process of raising the tanks, filtering the oil, and refilling the tanks. Simple tests like these will be described below. The breaker under test, however, must still be isolated from the circuit by air-break switches or by physically removing its connections. |

| Resistance Test |

| This test employs a dc source (such as a battery, a voltmeter, and an ammeter (Fig. 9-9). The resistance of the contacts is derived from Ohm's Law, using the equation, |

| where |

| R = resistance, in ohms |

| E = voltage, in volts |

| I = current, in amperes |

| A record of these values of resistance is kept, and any significant change in later tests determines the time for maintenance. |

| Figure 9-9 Voltmeter-ammeter method of resistance testing. |

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