SETUP WORKSTATION

SETUP WORKSTATION
Ass. Reprint 08/30/01
9/17/01
10:31 AM
Page 1
www.ept.ca
Setting up a people-safe product-safety workstation
by Dwayne Davis, technical services
manager, Associated Research Inc,
Lake Forest IL, represented by
Testforce Systems Inc., St. Laurent QC.
Test station layout using dual remote
test switches.
In setting up a safe workstation for
conducting electrical safety tests that
must be performed to meet the
requirements of agency standards as
specified by UL, CSA, EN or other bodies, addressing operator safety during
a test is just as important as ensuring
the safety of the end-product user.
The first challenge a manufacturer
faces is finding where to go to find
guidelines on how test stations should
be set-up. It is also common to find
that the individual responsible for setting up the test station may not have a
basic understanding of electricity or
the hazards involved.
The lack of awareness of the potential
hazards involved makes it very difficult
to build in the necessary safeguards to protect the operator against potential shock
hazards. Most often the focus is on setting
up the test area for maximum productivity.
Assembly operations may also be performed at the same workstation to balance
the production line. This makes it even
more critical to set up a safe workstation.
Assemblers not involved with the electrical
aspects of manufacturing the product could
inadvertently be exposed to electrical safety hazards.
Qualified personnel must have the
skills and techniques necessary to distinguish exposed live parts from other parts
of electrical equipment amid the hazards
involved. Exposed live parts are considered to be parts of the product which are
energized and which the operator may
come into contact with during the test.
Individuals responsible for setting
up the workstation must be aware of the
proper clearance distances for corresponding voltage levels. The operator should be
trained in safety related work practices
and procedures, and in emergency procedures required to release victim from
contact with exposed live parts or circuits.
A person setting up test stations must be
able to determine the degree and extent of
the hazard and the personal protective
equipment and job planning necessary to
perform the task safely.
For example, standards specifically call
out that conductive materials and jewelry
should not be worn by anyone working on
or near energized equipment, yet it is commonplace to see personnel working at electrical testing workstations wearing antistatic clothing and jewelry.
A test station cannot be considered safe
without the proper training of any individuals involved in or exposed to the testing.
In addition, the station needs to be configured to provide the operator with every
possible protection against exposure to
Operator uses a pistol style high voltage
probe with the capability to automatically
initiate the test by depressing the trigger.
Activation of high voltage requires a two
step action of retracting the probe shield
and depressing trigger.
hazardous voltages.
For guidelines regarding the proper set
up of an electrical testing workstation, turn
to the proposed European Norm Standard
prEN 50191 Erection and Operation of
Electrical Test Equipment. It is an excellent source document that is scheduled to
be accepted and published as a European
Standard and as an identical British
National Standard.
While not a standard in North America,
it has guidelines that are much easier
to understand as they specifically address
the set-up and operation of electrical
test equipment.
EN 50191 differentiates between test
stations with positive protection against
direct contact and those without. In a test
Reprint from the May 2000 issue of Electronic Products & Technology. ©2001 LVP Media Inc.
Ass. Reprint 08/30/01
9/17/01
10:31 AM
Operator tests stators with dual retractable
test probes. Once released the high-voltage
probes retract to prevent user contact with
high voltage.
station with positive protection against
direct contact, the device under test (DUT)
and all live parts of the test apparatus have
positive and full protection against direct
contact while the equipment is in an energized condition.
An example of full protection would be a
test hood that covers the entire product
and the test instruments, making it impossible for the operator to contact either
during a test without de-activating the
high voltage. Test stations without positive
Enclosure prevents the operator from coming
in contact with DUT while test is in progress.
Page 2
protection against direct contact should
only be used if it is not practicable to
achieve positive protection.
Some common reasons for setting up
test stations without positive protection
may be due to the physical size of the DUT
or requirements to manually test multiple
points which could prohibit the use of an
enclosure. However, testing of multiple
points does not necessarily mean that positive protection cannot be used.
Several new safety-testing instruments
are available with scanning matrixes that
can automatically apply voltage to multiple points of a DUT without operator
intervention.
EN 50191 recommends a number of
safeguards:
•Barriers or walls to separate the test area
from assembly areas. The distance between
the barriers and any parts that could
become live are specified in the standard in
relation to the maximum test voltage.
•Insulated enclosures or covers to prevent
access to the DUT. These covers should be
interlocked with the test instrument.
•Indicator lamps and warning signs. These
would provide visual indications that could
be incorporated in the test area to indicate
the operating status of the equipment
within view of all operators.
•Positive protection to guard against residual voltage must be incorporated. This
basically means that output shorting
devices should be used to discharge any
energy which may be stored in the DUT.
To protect operators at stations that do
not incorporate positive protection against
direct contact, here are some suggestions:
•Test station should be separated from
work areas. The use of walls and barriers
should be constructed to protect the people
standing outside the test area. The barriers should be constructed so visual contact
with the test operator can be maintained
from outside the test area.
•Test apparatus must be guarded against
unauthorized use, or unintentional operation. A lockout device should be incorporated into the design.
•Emergency switching equipment. This
provides operators with a quick way to cut
off all voltages that could result in danger.
At least one of the devices should be located outside the danger area.
•Test bench should be made of non-conductive material. This is required to isolate the
DUT during the test.
US information sources
If you are a manufacturer with a test
location in the US, the first place you may
look for guidance is to the US
Occupational Safety and Health Act
(OSHA) 29 CFR Part 1910, subpart S,
Electrical Safety Related Work Practices.
This standard used the US National Fire
Protection Association (NFPA 70E)
Electrical Safety Requirements for
Employee Workplaces as its source document in the development of the final standard.
Both standards provide background
information on electrical shock hazards,
nature of electrical accidents, and some
protective measures. They stipulate general requirements for employee training,
and advise that the personnel performing
these tests must be qualified, thoroughly
trained and be familiar with required
safety related work practices.
•Two-hand controls. If an insulated
enclosure cannot be incorporated in
the design of the workstation, the use
of two-handed controls may be an
alternative.
•Two safety probes. The operator can
either apply voltage to the probes by
manual operation or release the live
probes, which must at a minimum
safely insulate the user from the test
voltage if it remains active. Some
probes may include an automatic
switching circuit which would de-activate high voltage when the probe is
released. Two safety probes are specified which require the operator to use
both hands to test the DUT. This
prevents the operator from contact to
the device under test while the test is
in progress.
For additional information visit
our website at
www.asresearch.com
or contact us directly:
Tel: 1-800-858-TEST (8378)
Fax: 847-367-4080
E-mail: [email protected]
Reprint from the May 2000 issue of Electronic Products & Technology. ©2001 LVP Media Inc.
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