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
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
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
