AR-Dielectric Withstand Testing

AR-Dielectric Withstand Testing
Instruments for Electrical
Safety Testing . . . Since 1936
Dielectric Withstand Testing in a Production Environment
Performing a routine product safety test should not in itself represent a shock hazard to
the operator who is conducting the test, yet anytime you are working with an energized
circuit you must be aware of the hazards involved in performing the test and take the
necessary safety precautions. Operators should be properly trained to avoid the shock
hazards involved. The National Fire Protection Association, Standard for Electrical
Safety Requirements for Employee Workplaces NFPA 70E stipulates that only qualified
persons performing electrical work be permitted access to live parts. The NFPA 70E
standard is one of the primary standards that the Occupational Safety and Health
Administration (OSHA) 29 CFR Part 1910 subpart S Electrical Safety related Work
Practices is based upon.
What makes a person qualified?
NFPA defines qualified persons in the following manner:
A qualified person shall be trained and knowledgeable of the construction and
operation of equipment or a specific work method, and be trained to recognize
and avoid the electrical hazards that might be present with respect to that
equipment or work method. Such persons shall also be familiar with the proper
use of special precautionary techniques, personal protective equipment,
insulating and shielding materials, and insulating tools and test equipment.
It is the employer’s responsibility to provide safety-related work practices, maintain a
safe working environment and train the employees implementing those practices. One
way an employer can help ensure a safe working environment is by using electrical safety
testers with safety agency listings. Recognizing this OSHA requires that electrical
instruments used in the workplace be listed by a Nationally Recognized Testing
Laboratory (NRTL). Underwriter’s Laboratories (UL) is qualified as an official NRTL.
Therefore, in order to help meet OSHA requirements AR has several products with the
UL listing mark.
The degree of training required for the operators performing the product safety test is
highly dependent upon the set up of the product safety testing workstation. Whenever
possible the workstation should be constructed where there are no exposed energized
circuits and employ some positive means to protect the operator from coming in contact
with the device under test (DUT). When the electrical testing workstation does not
employ positive protection, the operator must be trained to recognize and avoid the
potential hazards.
13860 W Laurel Drive, Lake Forest, IL., 60045 U.S.A. • Phone: (847) 367-4077
Fax: (847) 367-4080 • E-mail: [email protected] • http://www.asresearch.com
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Instruments for Electrical
Safety Testing . . . Since 1936
The Dielectric Voltage Withstand or Hipot Test
The Dielectric Voltage Withstand or Hipot test is a routine production line test that can
be hazardous if the operator is not a qualified person, as they are working with voltages
that are potentially hazardous. Following are 10 examples of the knowledge that a
qualified person should have as it pertains to Hipot testing with exposed energized
circuits.
1. A qualified person should have a basic understanding of electricity, voltage,
current, resistance, and how they relate to each other. A qualified person should
also understand conductors, insulators and grounding systems.
2. A qualified person should have a working knowledge of the test equipment, the
tests that are being performed, and the hazards associated with the tests as well as
the circuits that are being energized.
3. A qualified person should understand the approach distances and corresponding
voltages to which they may be exposed.
4. A qualified person should be trained to understand the specific hazards associated
with electrical energy. They should be trained in safety-related work practices and
procedural requirements as necessary to provide protection from the electrical
hazards associated with their respective job or task assignments. Employees
should be trained to identify and understand the relationship between electrical
hazards and possible injury.
5. A qualified person should understand that the three primary factors that determine
the severity of electric shock are:
A. The amount of current flowing through the body
B. The path of the electrical current through the body
C. The duration or length of time the person is exposed
6. A qualified person should know that the human body responds to current in the
following manner:
A. 0.5 to 1 mA is the perception level
B. 5 mA a slight shock is felt, a startle reaction is produced
C. 6 -25 mA for women and 9 -30 mA for men produce the inability to let go
D. 30 – 150 milliamps results in extreme pain, respiratory arrest, ventricular
fibrillation and possible death
E. 10 Amps Cardiac Arrest and sever burns can occur
13860 W Laurel Drive, Lake Forest, IL., 60045 U.S.A. • Phone: (847) 367-4077
Fax: (847) 367-4080 • E-mail: [email protected] • http://www.asresearch.com
2
Instruments for Electrical
Safety Testing . . . Since 1936
7. A qualified person working on or near exposed energized electrical conductors or
circuit parts should be trained in methods of release of victims from contact with
exposed energized conductors or circuit parts.
8. A qualified person should understand that the test instrument is a variable voltage
power source and the current will flow to any available ground path. They should
be aware that contacting the device under test (DUT) during the test can result in
a dangerous shock hazard under certain conditions.
9. A qualified person should understand that if the return circuit is open during the
test then the enclosure of the DUT can become energized. This can occur if the
return lead is open or the operator lifts the return lead from the DUT while a test
is in process.
10. A qualified person should be made aware of the importance of discharging a
DUT. Lifting the high voltage lead from the DUT before the test is complete can
leave the DUT charged. When you are performing a Hipot test you are testing the
insulation between two conductors which is essentially a capacitor. This capacitor
can act as a storage device and hold a charge even when performing an AC test. If
the circuit is opened at the peak of the applied voltage then the DUT could even
under an AC test hold a charge. When the test is allowed to finish and the voltage
is reduced to zero the charge is dissipated through the impedance of the high
voltage transformer. Most DC Hipot testers today employ an output shorting
device to discharge the DUT, but the Hipot must remain connected to the DUT
throughout the test cycle.
This is just a partial listing of the knowledge required for qualified person to be able
to perform a Hipot test safely. They must be trained in safety related work practices
and proper work methods. Most accidents happen when the employee is distracted
while performing their assigned duties or takes a short cut in an effort to save time.
Many times you will find that the product safety testing workstations are set up for
maximum productivity rather than safety. If the test station is not set up with positive
protection against direct contact then a potentially hazardous situation can result.
Even the placement of the test equipment can create a potential shock hazard. For
instance, if the operator has to look away from the DUT to observe the test equipment
they could inadvertently contact an energized circuit or a return probe could
accidentally slip off resulting in an energized chassis.
Performing a Hipot test on a DUT with exposed energized circuits can be much safer
when you utilize a tester that employs the latest technology and safety features. Many
testers today have multiple shut down circuits to disable high voltage. These testers
use both adjustable high limit and low limit current sense circuits. The high limit
circuit will shut down the Hipot within 0.5 seconds if the adjustable current threshold
13860 W Laurel Drive, Lake Forest, IL., 60045 U.S.A. • Phone: (847) 367-4077
Fax: (847) 367-4080 • E-mail: [email protected] • http://www.asresearch.com
3
Instruments for Electrical
Safety Testing . . . Since 1936
is exceeded and the low limit circuit will shut down the circuit if a minimum current
flow through the DUT is not detected. The second situation could be due to an open
lead or the operator not making a good contact with the return lead. In either case the
DUT chassis could become energized. Another safety feature is the patented
SmartGFI® circuit, which is designed to sense if the DUT is floating or referenced to
earth ground (see figure 1). If the DUT is isolated from ground the GFI circuit is
enabled and monitors any current which flows back to earth ground and will send an
interrupt signal to shut down the high voltage if it detects any current in excess of 0.5
mA, thus protecting the operator. This sensing circuit is independent of the current
trip setting for the DUT which can set to a much higher current level.
Figure 1: Patented SmartGFI Safety Circuit
Engineering and work practice controls should be the primary factor in safeguarding
against the risk of injury. In order to provide for the highest level of protection safety
controls should automatically be in place and not rely on the involvement of the
operator. Likewise, personal protective equipment should not be the primary means
of protecting the operator. These types of safeguards are only effective should the
operator make a decision to utilize them.
The qualified person should also be trained in the care, use and inspection of any
personal protective equipment and insulating tools required to do the job. Qualified
persons should also perform a daily visual and functional verification test on the test
equipment. This is done to certify that the equipment is functioning properly and to
verify that the equipment will detect a fault condition. In order to help satisfy this
requirement AR has developed the VERI-CHEK® function, which is a built- in self
verification feature. All of AR’s new instruments include this feature. See figure 2 for
an example of how the VERI-CHEK® feature works. If personal protective
equipment such as high voltage gloves is used, then they must be inspected before
each use and electrically tested at a minimum of every 6 months. Any defects must be
reported immediately and the defective item must not be used.
13860 W Laurel Drive, Lake Forest, IL., 60045 U.S.A. • Phone: (847) 367-4077
Fax: (847) 367-4080 • E-mail: [email protected] • http://www.asresearch.com
4
Instruments for Electrical
Safety Testing . . . Since 1936
Figure 2: VERI-CHEK Self Verification Screen
It is a good practice to regularly review your product safety testing workstations and
the skill levels of your operators. Reviewing these guidelines in a regular interval will
help to limit potential shock hazards. Newer test instruments that include new
technology can also make testing safer. These things together with properly training
and educating your operators are the best means to prevent the risk of injury. We hold
free ½ day seminars throughout the year. These seminars can help manufacturers to
provide their personnel with proper training and education. Please contact Associated
Research if we can be of any assistance at 1-800-858-8378 or email us at
[email protected] You can also obtain additional information on safe testing
methods from our web site at www.asresearch.com.
13860 W Laurel Drive, Lake Forest, IL., 60045 U.S.A. • Phone: (847) 367-4077
Fax: (847) 367-4080 • E-mail: [email protected] • http://www.asresearch.com
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