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Understanding the Abnormal Operations Test

The “Understanding the Product Safety Tests” Series

The Abnormal Operation Test is a test that contains many different types of “abnormal operation”conditions (aka “fault” conditions). The product safety standards require that all products comply
with the 6 Hazards of Product Safety during normal operating conditions. The standards also
require the product to have adequate Shock & Fire Hazard protection during all single fault
conditions = the Abnormal Operation Test verifies that the single fault protection designed into
the product does its job when a fault occurs.

1)  The Purpose of the Test:

  • The product safety standards require that the product be suitably protected from shock and fire hazards in the event of any single fault condition (abnormal operating condition).
  • This test is performed on the overall product to insure that during a foreseeable abnormal operating condition, there is no Risk of Shock or Risk of Fire. Either of
    these hazards could cause serious injury or death, including the possibility of multiple
    deaths should a major fire occur.

2)  The Test Method: Essentially the goal is to try any one thing that could go wrong and make
sure that there is no shock or fire hazard. There are many different types of single fault
conditions to consider:

a) General Fault Test Considerations:

  • Multiple faults are never performed at the same time. However, a single fault may lead to other component failures as a result of the initial fault condition.
    These are considered part of the results and a skilled compliance engineer
    will examine the electrical schematic with an eye for identifying components
    to fault that could have a cascading fault effect = one short circuit could lead
    to excessive current through another component that fails and causes another
    failure, etc.
  • Critical limiting components must be certified in order to be relied upon. It is
    not considered a “fault” to bypass uncertified protection devices. For example,
    thermostats and temperature limiters must be certified or they will be
    bypassed during all tests including all abnormal operations tests. Fuses,
    circuit-breakers, and insulating materials must all be certified to be relied

  • Test duration will depend on how the product responds to the fault condition.
    In general, the test needs to continue until ultimate results are obtained. A
    circuit breaker tripping or a fuse opening may remove power to all circuits
    thereby quickly ending a test. Other times there may be no immediately
    observable result, but that can change over time. Products with a fault
    condition have been known to sit unresponsive for a period of time before
    catching fire. Most standards specify waiting up to 8 hours for a fault condition
    to play out.

  • Temperatures are not monitored during most abnormal operation tests as
    temperatures generally are not used as risk of shock or risk of fire indicators.
    However, there are a few standards and types of abnormal tests that require temperatures to be monitored during testing. This includes the overload and
    output short-circuit tests for isolation transformers using double or reinforced
    insulation systems.


 Insulation Faults: Basic insulation by definition is considered a single level of
protection – failure of any basic insulation is to be tested. Also, by definition,
operational insulation may provide fire hazard protection. Consequently, a fault is
applied to any operational insulation that may lead to a fire. The objective is to find
any component faults that lead to a fire, and then verify that the product’s enclosure
properly contains the fire.

c)  Electrical Component Faults: Single component faults are to be performed on
electrical components – open and short circuit conditions based on a review of the
product’s electrical schematic diagram. Any certified double insulated components
are not faulted because that would be considered a double fault (and we only are
permitted to perform single fault conditions). Certified double insulated components
have already been tested to insure that if any internal single level of insulation fails,
the component does not develop a shock or fire hazard.

  1. We do not conduct component fault tests to ground – that would always blow
    the fuse and/or trip the breaker. Instead, for products provided with a
    Protective Earthing terminal (P.E.), we do testing on the ground system to
    insure it is reliable if there is a component fault to ground.

d) Mechanical Faults: Motor locked rotor (including fan motors) and failure of other
electro-mechanical parts. Overloading of mechanical parts and loading bearing
systems are done separately as part of the Risk of Injury review and testing.

e) Thermal Faults: Blocked vents and otherwise inhibited product ventilation from a
single fault event. Worst case is often considered pushing the product into a corner
or covering one set of vents – tests identified and configured such that they represent
a single fault condition. Installation instructions and intended use environment
should be also consulted in making these determinations.

f) Other Faults: All single fault conditions that could lead to a Risk of Fire or a Risk of
Shock must be identified and performed. For example, dual voltage rated products
(i.e. 120/230VAC) using a voltage selector switch, voltage mismatch testing is done
to represent the single fault condition of having the switch in the wrong position.

3) Test Configurations


Voltage Rating: For products that have a voltage rating range (i.e. 100 – 240VAC),
the highest rated voltage is generally used for this testing – the goal being to have
the highest available energy during the fault condition.

b) All Abnormal Operation Tests: The product is to be placed on tissue paper and
covered with cheesecloth = these materials serve as the “fire indicators” and are
further defined with specifications in the standards. If either of these materials is
charred or discolored, the standard concludes that a fire hazard has occurred – which
is a test failure.

c) Test Preparation: The product is subjected to the worst case normal operating
conditions before the fault condition is applied. Which usually means that the product
must be properly prepared so that the fault condition can be imposed while the
product is operating normally. For electrical component faults, that means installing
leads that extend from the product to a knife switch that can be actuated to initiate
the component fault condition during normal operation.


The Test Objectives: The objective is to identify any failure of the product insulation system
that could lead to a shock hazard to the user OR identify any failure in the product that
could result in fire escaping the enclosure and igniting the supporting surface or nearby
materials. The fault condition tests themselves do not reach these conclusions. After each
fault condition, additional testing and inspection must be performed to determine if the test
results are compliant. The test objectives are contained within the multiple pass/fail criteria
for the fault tests.

  1. Shock Hazard Pass/Fail: After each abnormal operation fault condition test, the
    product and in some cases insulating components that could be damaged by the
    fault condition are hipot tested (dielectric voltage withstand tested) to insure that the
    risk of shock insulation system remains reliable. With certain product
    standards/designs, leakage current testing may also be performed to determine if a
    shock hazard exists.

  2. Fire Hazard Pass/Fail: Visible internal fire and the resulting smoke are not relevant.
    After each abnormal operation fault condition test, the tissue paper under the product
    and the cheese cloth covering the product are examined for charring or other
    discoloring. If these materials are unaffected, the test results are compliant. Note
    that hot smoke will usually discolor the cheesecloth resulting in a test failure.

As you can see, we don’t simply perform the tests because they are in the standard. Each test in
the standard has a set of objectives that relate to the 6 Hazards of Product Safety. The Abnormal
Operation Tests are performed as part of the Risk of Shock and Risk of Fire compliance review.
Verifying reliability of the product’s electrical insulation system is crucial to insuring the product
continues to provide protection from a Risk of Shock, a potentially serious hazard that could lead
to death by electrocution. We are also confirming that if any product fire occurs, it is contained
within the product’s enclosure so that the fire does not spread and threaten all building occupants.
It is therefore an extremely important test – another test that directly saves lives.

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