310.2

NAVSEA 0900-LP-060-2010 Series recommends the use of the General Radio Type 1644A, 1863, or an equivalent instrument for ground testing electric motors during troubleshooting, or prior to and after reconditioning or rewinding. Using these units for ground testing permits the application of voltage over an extended time period to determine the condition, and total value, of the motor's insulation resistance to ground.

To use the Type 1863, you must know the parts of the unit, be able to hook the unit to the motor to be tested, know how to convert the insulation resistance-to-ground readings to megohms, and know where to record the readings.

Setting up the General Radio Megohmmeter, Type 1863

Place the instrument on a flat, level surface with the handle away from the operator. Reach over the instrument with one hand and place that hand on the handle. Place the other hand on the instrument case to balance it. Depress the handle to raise the instrument off the gasket.

Do NOT drag the instrument on the gasket as it is tilted; this will stretch and distort the gasket.

As the instrument clears the gasket, tilt the instrument to a comfortable reading position.

1. The POWER switch is a two-position toggle switch to the operator's lower left. This switch turns power ON and OFF.

2. A 4-inch METER with a plastic cover that indicates the value to be multiplied by the multiplier switch.

3. A SET [4] HIGHEST RANGE screw to adjust the high end of the meter scale on highest resistance range to compensate for offset current.

4. A SET [4] setscrew adjusts the high end of the meter scale to compensate for voltage offset in the voltmeter.

5. The GUARD terminal post for guarded measurements is located adjacent to the metal terminal to permit connection by the shorting link.

6. The GROUND TERMINAL grounds the UNKNOWN by means of the captive shorting link. The shorting link is permanently attached to this terminal.

7. The +UNKNOWN terminal connects the + side of the UNKNOWN to the megohmmeter.

8. The -UNKNOWN terminal connects the - side of the UNKNOWN to the megohmmeter.

9. The DANGER warning light glows red when the function switch is in the CHARGE or MEASURE position.

10. The seven-position MULTIPLIER switch selects the resistance range and is used to compute the resistance reading in conjunction with the meter reading.

11. The FUNCTION switch is a three-position toggle switch marked MEASURE, CHARGE, DISCHARGE used to select the operating mode applied to the UNKNOWN.

12. The five-position TEST VOLTAGE selector switch selects a voltage of 50, 100, 200, 250, or 500 volts to be applied to the UNKNOWN. (UNKNOWN refers to the component being tested.)

Megohmmeter, Type 1863 (Front)

1. The POWER PLUG HOLDER holds the power plug in place after the power cord has been wrapped inside the cover.

2. The OUTPUT JACK provides a dc voltage output for recorder operation.

3. The LINE VOLTAGE switch connects wiring of the power transformer for either 100- to 125-volt or 200- to 230-volt ac input.

4. The 1/8 AMP fuse (with holder) provides meter protection for 100- to 125-volt ac operation.

5. The 1/16 AMP fuse (with holder) provides meter protection for 200- to 230-volt ac operation.

Operating the Type 1863 Megohmmeter

Ensure that the POWER SWITCH is in the OFF position.

The cord is secured in place by plugging it into a dummy receptacle in the back of the case. It must be unplugged to uncoil the cord.

Uncoil the power cord from the back of the instrument case. Plug the cord into a 115-volt, single-phase, 60-hertz outlet.

Windings not under test must be grounded.

Connect the winding leads to be tested.

The following procedure is used to measure the motor insulation-to-ground.

Instrument lead connections

• Shield to the GUARD terminal
• + terminal to the motor frame (shielded lead)
• - terminal to the winding to be tested

Connect the shorting link between the metal terminal and the +UNKNOWN terminal.

Set the MULTIPLIER switch to the lowest range.

Set the function switch to DISCHARGE and allow 1 minute of warmup time.

Set the TEST VOLTAGE switch to 500.

Lethal voltage is present on this instrument.

Set the POWER switch to the ON position.

Set the function switch to the MEASURE position.

Rotate the MULTIPLIER switch clockwise until the meter reads less than five. Take the reading for 1 minute.

If the meter "pegs" to the left, it indicates a ground.

Megohmmeter, Type 1863 (Rear)

Click on image to enlarge.

Typical Motor Data Sheet (Electrical)