Lesson 10: Test Instruments - How to use a Megohmmeter

A cable is considered good if it reads one megohm for each kilovolt of cable rating.

True

During a megohmmeter cable test, leakage current can take two forms: current through the insulation, and current ? . a. along the surface of the insulation b. leakage at the pothead c. leakage into the neutral/ground d. tracking at insulators

a. along the surface of the insulation

When performing a time resistance test on a cable, the megohmmeter test usually runs for ? , depending on the meter manufacturer and the voltage applied. a. 1-9 minutes b. 1-10 minutes c. 5-15 minutes d. 6-20 minutes

b. 1-10 minutes

Insulation resistance opposes ? current either through or over the surface of the insulation when voltage is applied. a. initial b. leakage c. primary d. secondary

b. leakage

A megohmmeter can only be used to test the insulation of cables.

False

A megohmmeter test on a section of faulted underground cable can pinpoint the area of the fault.

False

Megohmmeter tests are extensive; a simple pass/fail test is not available when using a megohmmeter.

False

OSHA 1910.268(o) calls for safe work practices to be in place when doing high-voltage testing.

False

The guard lead from a megohmmeter reads the voltage leakage that might be present when checking a cable.

False

A megohmmeter test is a nondestructive test. This means that a setting of ? should be used on a secondary cable rated up to ? . a. 500 / 600 V b. 600 / 500 V c. 1,000 / 600 V d. 5,000 / 4,000 V

a. 500/ 600V

Most megohmmeters are rated at ? DC or higher. a. 600 V b. 900 V c. 1,000 V d. 10,000 V

c. 1,000V

A megohmmeter uses a high ? voltage to perform an insulation test on a cable. a. AC b. constant/steady/filtered c. DC d. variable

c. DC

When calculating the resistance of a circuit, ? Law applies. a. Kirchhoff's b. Norton's c. Ohm's d. Thevenin's

c. Ohm's

When using a megohmmeter to test a faulted section of cable, before the test is conducted, the cable must be ? . a. cable prepared to specifications b. checked for current c. grounded to drain any capacitance d. sealed from the environment

c. grounded to drain any capacitance

When preparing for a megohmmeter test on a section of underground cable, both ends of the concentric neutral must be ? . a. bonded to the conductor under test b. connected to separate ground rods c. isolated from ground d. tied together

c. isolated from ground

One reason to perform a megohmmeter test would be if there was suspected damage to the insulation by a ? . a. CT drawing current from the cable b. faulty ground c. related component failure d. solid neutral to ground connection

c. related component failure

A megohm is equal to ? . a. 100,000 Ω b. 250,000 Ω c. 500,000 Ω d. 1,000,000 Ω

d. 1,000,000Ω

A factor that can cause insulation to degrade is ? . a. electrical stress b. mechanical stress c. thermal stress d. all of the above

d. all of the above

One of the things maintenance testing of cable indicates is the ? . a. insulation thickness of the cable b. kVA capability of the cable c. presence of water treeing d. remaining life of the cable

d. remaining life of the cable

While performing a megohmmeter cable test, if the meter shows 0, it is probably a ? fault. a. high-resistant b. low-resistant c. series d. shunt

d. shunt