The electrical industry has always had a
fascination with testers. There are testers for GFCIs, voltage
drop, circuit polarity, circuit continuity and now the latest
addition—the arc-fault circuit interrupter (AFCI) tester.
NEC 210.12 requires AFCIs on 15- and
20-ampere branch circuits that supply bedrooms in dwelling
units. The intent of the AFCI is to detect hazardous arcing
and turn off the circuit in order to reduce the potential of
fire from an arc. AFCIs are available from a variety of
manufacturers and have been installed in thousands of homes.
To capitalize on this new device, the AFCI
"tester" has shown up in the marketplace. Many
electrical inspectors and home inspectors have purchased the
tester with the idea that it will tell them whether an AFCI is
functioning properly. Unfortunately, confusing and conflicting
results can occur.
Testers of many kinds can be very useful
tools for accomplishing specific tasks. Some are more useful
than others. Before deciding whether a tester may be useful
for installation and inspection of AFCI circuits, you might
find the following facts helpful.
The
Nature of AFCI Designs
The UL standard for AFCIs (UL 1699) sets forth the
requirements for the proper functioning of an AFCI. A number
of the tests are efficacy tests that subject the AFCI to
various arcing scenarios. The AFCI must detect the arc and
open the circuit before the cotton fire indicator ignites at
the arcing location. In addition, the AFCI has to be able to
resist tripping under a number of normal arcing scenarios (e.g., thermostatically controlled contacts) that
are established in the standard.
It is important to recognize that the
standard does not set forth the method that a manufacturer
must use to detect the hazardous arcing conditions and resist
the normal arcing conditions. Manufacturers can utilize
different and unique methods to achieve the expected result.
Therefore, Manufacturer A may use one algorithm for detection
and Manufacturer B may use something completely different.
Both meet the standard and are acceptable AFCIs, they just get
there by traveling down different paths.
This is an important concept to grasp in
order to understand why the testers may not necessarily work
properly in the field.
It’s
An Indicator, Not A Tester
The reality is that there is no portable AFCI tester on the
market today. If one looks closely at the products, they carry
a listing as AFCI indicators. UL 1436, Outlet Testers
and Similar Indicating Devices, is careful to define an AFCI
indicator, not an AFCI tester.
In fact, the standard recognizes the
differing nature of arc detection and requires a marking or
notation in the instructions1 that states:
"CAUTION: AFCIs recognize
characteristics unique to arcing, and AFCI indicators produce
characteristics that mimic some forms of arcing. Because of
this the indicator may give a false indication that the AFCI
is not functioning properly. If this occurs, recheck the
operation of the AFCI using the test and reset buttons. The
AFCI button test function will demonstrate proper
operation."
Because of the variation in AFCI designs,
an AFCI indicator that may work with one manufacturer’s
product may not work properly with another. It is also
important to remember that AFCI manufacturers are constantly
improving their products. These improvements can also result
in an AFCI that functions properly and meets that standard but
no longer works with a specific AFCI indicator.
Last, the manufacturer of the AFCI
indicator will not be familiar with the tolerances that are
acceptable within the design of the AFCI itself. The AFCI
indicator may function correctly with a device that falls into
the middle of its tolerance band, but not work with one that
is at the high or low end of the tolerance band, even though
all of the devices represent a properly functioning AFCI.
Use
the Test Button
To determine whether an AFCI is functioning properly, use the
test button on the AFCI. Pushing the test button should result
in the device opening. This is not a mechanical test. Pushing
the test button imposes a simulated arcing condition on the
circuit and the AFCI must be able to detect that arcing
condition and open. If the device does not open, then the AFCI
should be replaced. If the device opens and it can be reset,
then it is a properly functioning AFCI and it has been tested.
Don’t
Toss a Perfectly Good AFCI
As stated earlier, the best method for testing an AFCI is the
integral test button. If the test button shows proper
operation, then the AFCI is okay. This is true even if your
AFCI indicator device does not trip the AFCI. It is
unfortunate that some properly functioning AFCIs have been
replaced in the field due to a false indication of their
status from an AFCI indicator. Upon return to the
manufacturer, the AFCI is evaluated and frequently found to be
functioning properly.
Summary
The bottom line is that the test button on the AFCI is the
only recognized method for testing the proper operation of the
AFCI. An AFCI indicator may be a nice way to determine if a
particular circuit is connected to an AFCI, but it provides no
definitive answer on whether an AFCI is properly working or
not.
1UL 1436, paragraph 31.8.1(f)
Jim Pauley is vice
president, Industry and Government Relations for Schneider
Electric-North American Operating Division. He is a member of
NEC Code Panel 2, the NEC Technical Correlating Committee, the
NFPA Standards Council and the ANSI Executive Standards
Council.
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