Armstrong World Industries 302 1 Determining Capacitance MFD Rating with a Test Cord, Example

TROUBLESHOOTING Magic-Pak: HW/HWC

9-8

Ammeter

(10 Loops)

A

Fuse

Nominal

VoltageVoltmeter VCapacitor

To Be Tested

Source

FIGURE 9-1 Determining Capacitance (MFD) Rating with a Test

Cord

Before starting the test, take a reading of the line voltage at the outlet that will be used.

Double check the connections, making sure that the amp meter is on. Plug the test leads into the wall outlet. Wait a few seconds and read the amp meter (CAUTION: there is only approximately ten seconds to do this or the capacitor could be damaged). Unplug the jumper and record the readings.

Using the calculator, divide the amp meter reading by ten (the number of loops in one of the test leads). This is the correct amp reading which is needed to finish the calculations. This information and the voltage at the outlet is all that is needed to calculate the capacitance of the capacitor.

2650 x Amps

= Capacitance (MFD)

Volts

In the following calculation, a constant multiplier (2650) is used for 60 Hz electrical systems.*

2650 x 1 Amp

= 23 MFD

115 Volts

Example

This calculation provides the actual capacitance of the capacitor. Com- pare this reading to the listed rating on the capacitor. It should be within +/– 10% of the actual capacitor rating. If it does not fall within this range, the capacitor is defective and should be replaced.

The capacitor should always be checked before replacing an electric motor. Eliminate the capacitor as a possible cause of the problems before the decision is made to replace the motor. A good practice is also to replace the capacitor whenever a motor is replaced, as the capacitor does have a service life cycle. The capacitor is a very important part of the motor electrical system. Always check the capacitor along with the motor when a fault is noted.

*For 50 Hz electrical systems, use 3180 as the constant multiplier. SRM-HW/HWC

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