Using the Wattmeter

CAUTION:

Make the connections to the wattmeter(s) and place the selector knob(s) on “OFF” before turning on the power to your circuit or device.

NOTE:

A voltmeter and Ammeter must be used for power measurements in order to help determine power factor and appropriate voltage and current ranges.

SINGLE PHASE POWER: (Refer to Figure 1)

1. Select one of the wattmeters.

2. Place the Ammeter in series with the load and the voltmeter is parallel with the load as shown in Figure (1). (Refer to the instructions on using the A.C. Meters if necessary).

3. Connect dark blue terminal of the Ammeter and the light blue terminal of the Voltmeter to both the dark blue terminal of the amps coil (of the wattmeter) and the light blue terminal of the volts coil (of the wattmeter).

4. Connect the orange terminal of the amps coil to the load and the yellow terminal of the volts coil is connected to common (ground).

5. Turn on the power to the circuit or device and read the voltmeter. If the voltage is between 150 and 300 volts, turn the selector knob clockwise to “300V” and choose the 2A, 4A, or 8A setting based on the current shown on the ammeter. If the voltage is less than 150 volts, follow the above routine but turn the selector knob counter-clockwise.

 

THREE PHASE POWER: (Refer to Figure 2)

(The procedure below only works for a balanced load)

1. Place the ammeter and voltmeter in either one of the two configurations described below.

a. Place the ammeter in series with the phase A line and the voltmeter across phase A and phase B using the connections described for the single phase case.

b. Place the ammeter in series with the phase B line and the voltmeter across phase B and phase C again using the single phase case.

2. Make the remaining connections shown in Figure (2) using the terminals described in the single phase case.

3. Turn on your circuit or device power and adjust the wattmeter knobs as described for the single phase case.

4. Take the sum of W1 and W2 readings. This is the total wattage. Exception: if the pointer of W1 goes off scale to the left, reverse the connections to the AMPS coil of the wattmeter. The total wattage is the difference W2-W1.

5. In all cases, calculate the power factor angle 0 from:

1 Phase Wattmeter Connections

Figure 1: 1 Phase Wattmeter Connections

Figure 2: 3-Phase Wattmeter Connections

Figure 2: 3-Phase Wattmeter Connections