Current Tests: Part 2

Air Conditioner Current Test

Some motors are designed to reach rated rpm faster than other motors by using a special starting winding or capacitor circuit on startup, then switch over to the normal running circuit once normal rpm is reached. Motors used in air conditioners are of this type. Certain types of test jigs are available commercially.

The initial surge current of an air conditioner that requires a 15-ampere circuit is over 15 amperes, and this high current flows momentarily every time the motor starts up, when you first turn the equipment on, and whenever the compressor comes on. Therefore, it is recommended that a time-delay circuit breaker be used, and the air conditioner be on a separate, dedicated circuit. Set the ammeter range higher than 15 amps to allow for the surge; the normal run reading while the compressor is on will likely be less than 10 amps, and while the compressor is off, around 3 amps if the circulator fan is running, and zero if it is not.


Usage Tests

Usage testing refers to power usage more than it does to current usage, and it is the measure of the power used over a period. Essentially, a wattmeter is connected to the circuit, either permanently or for prolonged periods, to keep track of power consumed over specific lengths of time.

The most common type of usage tester, or wattmeter, is the utility’s monitor that is connected across the main input service line before it enters the building or, inside the building, before it enters the main service box. It monitors the line voltage and all current flows to the building and gives usage readings in kilowatt-hours (kWh).

In other applications, separate circuits or equipment can be monitored to compare the power usage of the different systems. In a shopping mall, for example, the heating and/or cooling systems could be monitored separately, as well as the lighting systems, and people-moving systems, such as escalators and elevators. In industrial applications, individual production systems could be monitored. All of these usage monitoring systems give readings in kilowatt-hours.


Load Tests

Typically, when a circuit is rated to carry a certain maximum current, say 20 amperes, there is little or no difference when a low current flows or when a higher current flows- as long as the current stays within limits. However, when certain problems exist, such as a high-resistance connection, the higher current that flows through such a connection will cause a voltage drop that will result in the line voltage in that circuit being reduced. How much the line voltage drops depends on how bad the connection is. In a case such as this, if the line voltage was tested when there was little current flowing, a normal reading might be obtained, because the line voltage drops under heavier load currents.

When circuits are suspected of this problem, a load tester can be used to simulate load conditions and read out the percentage that the line voltage drops as loads are simulated. A typical example of a load current simulator is one that can be set to draw 0, 10, 15, or 20 amperes in sequential steps. Do not set the simulator for a 20-amp load on a 15-amp circuit.