12
5.
Read watts directly on the lower arc of the scale. Use the figures correspond-
ing to the range being used.
6.
In cases where the momentary load exceeds the limits of the 1500 W range,
such as the starting current of a motor, the white lead from the Break-In Plug
may be connected to the 300V terminal and the 3000W range used.
4.8
AC Watts 0-600, 0-3000, Using Break-In Plug
(Line Voltage 0-300)
1.
An adapter is required to connect from 120V to 240V line (see paragraph
4.3). The Break-In Plug will not connect directly into a 240V line. Therefore,
it is necessary to construct an adapter plug. Refer to Figure 4-3 for adapter
make-up and test connections.
Figure 4-3. Break-In Cable Assembly and Cable Adapter Set
2.
Connect the white lead from the Break-In Plug (see Figure 4-1) to the 300V
meter terminal. Connect the black leads to the ±V and ±A terminals.
3.
Connect the red lead from the Break-In Plug to the 3A terminal. The line on
the panel between the 300V and 3A terminals indicates that the 600 watt
range is being used. When the red wire is connected to the 15A terminal the
range is 3000 watts as indicated by the line on the panel connecting the
300V and 15A terminals.
4.
Insert the Break-In Plug into the 240V adapter socket and the adapter plug
into a 240 VAC source.
5.
Plug the appliance to be checked into the female adapter and the male end
of the adapter into the Break-In Plug.
6.
Press the WATTS pushbutton all the way down.
4.9
Determining Power Factor
1.
In an AC circuit containing only resistance, such as a toaster, the power will
be approximately equal to the product of the volts and amperes. However,
when the circuit contains reactance, such as a motor, the power will be less
than the product of the volts and amperes because of the power factor.
2.
The power factor of a circuit can be determined with the Model 390-2 in the
following manner. Take the voltage, current and power readings of the circuit
under test. Since unity power factor results when the power is equal to the
PLUG INTO 240 VAC OUTLET
120 VAC FEMALE
CONNECTOR
BREAK-IN PLUG
120 VAC MALE
PLUG
240 VAC FEMALE
CONNECTOR
PLUG IN APPLIANCE HERE
240 VAC MALE
PLUG