C4 LT3 Flashcards
What is the purpose of using a Megohmeter?
Measure insulation resistance
What should be done to discharge the capacitive charge after testing?
Use discharge button or ground each conductor
What is the primary use of a megger?
To test the insulation of electrical equipment for resistance changes.
What should be done after testing the insulation of motor leads?
Test conductors feeding the motor
What does a major change in the insulation’s resistance value indicate?
That the electrical equipment could fail.
How should conductors feeding a motor be tested?
Disconnect from circuit
What hazard can be created when testing long runs of conductors in a conduit with a megger?
Potential shock hazard
How should the bare ends of conductors be protected against shock?
Electrical tape or insulated wire connector
What feature do most digital meggers have to prevent shock hazards?
Discharge feature
What should be done after turning on the megger and noting the readings?
Test each individual conductor to ground.
If a digital megger lacks a discharge feature, what is the recommended safety practice?
Ground the conductor before and after testing
What should be done after testing conductors to ground?
Test each individual conductor to other conductors in the cable or conduit.
How should you drain the capacitive charge on the conductor after completing the test?
Discharge using the megger or to system ground
What are Digital insulation testers commonly referred to as?
Meggers
List some causes of insulation deterioration.
Mechanical damage, fault currents, excessive heat, oil, moisture, voltage stresses.
What should you do before testing insulation with a megger?
Refer to manufacturer’s instructions
Besides testing insulation resistance, what else are meggers used for?
Checking conductors for grounds, shorts, and opens.
How should the megger voltage be set for insulation testing?
Not more than rated voltage of equipment
What is the maximum voltage most ohmmeters can supply?
Up to about 9 volts
What should be tested after the motor leads have been tested to ground?
Insulation between motor leads
What should be checked before using a megger?
Maximum voltage rating of the conductor or component
Where should one of the megger leads be connected?
To the ground of the electrical system
What should always be referred to for testing procedures and features of the test equipment?
Manufacturer’s instructions
Where should the other test lead be connected during testing?
To the bare end of the conductor under test
What does a high megohm reading indicate on a megger test?
Good insulation and no short to ground.
What should the reading be when testing between conductors?
A very high megohm reading.
What does a megger provide to ensure the insulation will not break down?
High enough test voltage
What should you do after draining the capacitive charge on the conductor?
Do Self-Test 3 and check answers
What range of voltages can a megger supply?
250 volts DC to 5000 volts DC
What caution should be followed when using a megger?
Never use on a live circuit
What are the steps to test the conductors feeding a motor or equipment?
Connect one megger lead to frame, other lead to motor lead, push test button, read display, repeat for all leads, should be at least 1 megohm or higher
What relationship exists between voltage rating and insulation resistance?
Directly proportional
