Test 6: GFCI (Ground Fault Circuit Interrupter) Testing
A ‘GFCI’ can protect personnel from shock hazards. The CT70 tests GFCI circuits by forming a Hot-
Neutral imbalance, leaking small amounts of current (6 to 9 mA) from Hot to Ground through a fixed
resistance.
A good GFCI circuit will sense this imbalance and switch off the power. The CT70 displays the
current value in mA. To test a GFCI circuit:
1. Plug the meter into the receptacle under test.
2. Press the CT70 GFCI button to enter the GFCI test mode menu.
3. GFCI is the default test and the letters ‘GFCI’ should appear on the lower side of the meter’s
display. If not, press the ► button once to switch to ‘GFCI’.
4. Press the GFCI button again to start the test. The current that is leaked to ground will
display. The rotating display affect lets the user know that the test is in progress.
5. The GFCI circuit should typically trip within 200ms (the meter’s display will switch off
because the power has been removed by the GFCI circuit).
6. When the GFCI circuit is reset, the CT70 will display the elapsed time from start of test to
power down.
7. Press any button to return the meter to normal operation mode.
8. If the GFCI circuit fails to respond in 6.5 seconds, the CT70 stops the test automatically and
‘OL’ will display on the meter.
Notes:
1. To test a GFCI circuit on a two wire system, a three-to-two wire adaptor must be used with the
adaptor manually connected to ground (cold water pipe, for example).
2. Appliances connected to the circuit under test should be disconnected to avoid measurement
errors.
Test 7: EPD (Equipment Protective Device) GFCI Testing
An EPD device can protect equipment as well as personnel. The CT70 tests EPD circuits by forming
a Hot-Neutral imbalance, leaking current from Hot to Ground through a fixed resistance. A larger
amount of current (30mA) is used than would normally be used to test a standard GFCI (6 to 9mA). A
good EDP/GFCI circuit will sense this imbalance and switch off the power. The CT70 displays the
current value in mA.
To test an EPD/GFCI circuit:
1. Plug the meter into the receptacle under test.
2. Press the CT70 GFCI button to enter the GFCI test mode menu.
3. GFCI is the default test and the letters ‘GFCI’ will appear on the lower left side of the meter’s
display. Press the ► button once to switch to ‘EPD’.
4. Now follow steps 4 through 8 in Test 6 (GFCI) above.
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