CT70 V7.0 09/10
9
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 trip within the time specified by UL recommendations (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 the GFCI button again 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.
UL Guideline: T = (20 / I) * 1.43
Where: T = milliseconds (ms) and I = milliamps (mA)
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.
GFCI Troubleshooting Suggestions
Problems Likely
Causes
Probable Solutions
GFCI does not trip within trip time
GFCI may be installed
incorrectly
Verify that the wiring complies
with the manufacturer’s
directives and with NEC
GFCI does not trip
Defective GFCI
Check ground and other
wiring. Replace GFCI if
necessary
