Outlet tester

[Barry Adair]

http://ecmweb.com/mag/electric_think_gfci/

GFCI testers. If you're from Missouri and simply don't believe the internal test circuit, then you need to exercise care in selecting the GFCI tester and in interpreting the results. It wasn't until the 1993 Edition of UL 1436, Safety Standard for Outlet Testers and Similar Devices, that the requirements for GFCI testers were coordinated with the requirements for GFCIs themselves. Testers that are not UL listed and UL-listed testers produced prior to 1993 may contain test circuits that do not properly test the GFCI. Indeed, they may indicate an unsatisfactory test when the GFCI is functioning fully in accordance with the UL GFCI standard.

Some testers not meeting UL 1436-1993 have timing circuits that limit the test current to a duration of 200 ms. If the GFCI takes more than 200 ms to trip (as permitted by UL), these testers may never trip some GFCIs that are in full compliance with UL requirements. Therefore, if you choose to use a GFCI tester, make sure it's listed to the 1993 Edition of UL 1436.

Some GFCI testers are relatively simple circuit testers with an additional test button. Others have milliammeters or dials that can be used to select various test currents. When using any of these more sophisticated testers, do not assume that it's accurately checking the calibration of the GFCI. There is very likely some capacitive leakage and possibly some harmless ground fault leakage "preloading" the GFCI. Consequently, a GFCI that is tripping within the UL time/current requirements may, according to the tester, be tripping at 3mA. In this case, the tester is simply giving a misleading reading.

Reverse polarity. Since testers establish a test circuit between hot and equipment ground, if the receptacle into which the tester is plugged is wired with reverse polarity, there will not be a voltage across the tester and test current will not flow. The GFCI will not trip and thus the GFCI might erroneously be considered defective.

Testing GFCIs on nongrounding circuits. Testers should not be used to test GFCIs installed as replacements for two-wire receptacles on nongrounding circuits. By design, GFCI testers will not test a GFCI protecting a 2-wire circuit and can expose the user to a potential shock.

The test button integral to the GFCI applies the test current between hot and neutral. This is not the case with GFCI testers; the test current in these devices is applied between hot and the equipment ground. Therefore, if there is no equipment ground, no test current will flow. If there are any exposed metal parts connected to the receptacle grounding contact (such as a metal face plate or a weatherproof cover), they will be energized by the test device. Since some of the test devices apply up to a 30mA test current; using such a tester on a 2-wire circuit while touching a metal cover plate could result in an uncomfortable shock.

Keys to testing GFCIs.

* Use the GFCI integral test button.

* Check for line-load reversal using the GFCI integral test button supplemented with a lamp or appliance.

* Be sure that any GFCI tester used is listed to the current UL standard.

* Do not use GFCI testers on two-wire nongrounding circuits.

Conclusion

The use of GFCIs, both required and otherwise, has mushroomed over the years, from just underwater swimming pool lights in 1968 to 33 references in the 1993 NEC, with even more to come. Now that GFCI installations number in the millions per year, repetitiveness can result in complacency. Not all GFCIs are alike. The installation layout needs to be evaluated and the most appropriate GFCI selected for the job, and you must adhere to all wiring instructions and markings.

[Jim Port]

The newest GFIs will not reset if the line and load are reversed. They are also supposed to have an end-of-life component so that if they have failed the power is cut unlike the older ones that stayed on and made you think you had protection.

[Jeffrey R. Pope]

Originally Posted by Jim Port

Jeff, could you expand on this? If UL and the device manufacturers tell you to use the test button, why would this not be sufficient?

I have often found (when using the built-in test button) that the mechanism will "trip," but will not open the circuit. So the simple push-button test is not definitive.

My protocol is to trip the circuit - either internally or by introducing a simulated ground fault - and then verifying with one of my instruments that the circuit has opened.

If the GFCI device is defective, an externally introduced ground-fault will not trip the internal circuit-tester, nor will it open the circuit, so I consider the external method to be more reliable.

A home owner relying on the internal test button without additional verification, may be lulled into a false sense of security believing the GFCI is operational when, in fact, it is not.

Additionally, many older GFCI devices will trip and open the circuit only when a large fault is introduced. My SureTest provides only a 7.4 ma load for a maximum of 6.5 seconds to determine proper operation.

I tested one this morning that would not trip at 7.4 ma, but tripped at 2.8 amps of impedance. The internal test button worked every time I tried it, but the load required to actually open the circuit was too great. Again, this gives a false impression that the device is functioning "properly."