Most of my equipment is subject to EN60950 and UL1950. These standards are
not as conservative or specific as to testing for prevention of external
fire hazards as some other standards such as EN60065 and UL 2044. Therefore,
I am attempting to creating a more conservative test method for our
products. Before I present this method to our engineers, I want to ensure
that it is sufficiently conservative without going overboard. Your comments
would be welcome.
Fire Hazard Design Requirements for Equipment Intended for Mounting
In Fixtures, Furniture and Similar Partial Enclosures
Scope: These requirements apply to all electrical equipment intended for
mounting in partial enclosures with confined spaces that restrict
ventilation. Partial enclosures typically enclose the equipment on five
sides. Partial enclosures include shelves, cabinets, desks, and mounting
fixtures. This document does not apply to equipment intended for mounting in
full enclosures. The requirements in this document supplement the standard
design and test requirements specified in the safety standards. A
requirement of this document shall have precedence unless it is in conflict
with the relevant safety standard.
Design Requirement: The equipment shall be designed such that it is highly
unlikely that an external fire will start under normal conditions, failure
conditions, abnormal operation or foreseeable misuse.
Normal Test Conditions: The tests shall be performed under the most
unfavorable combination of supply voltage, frequency, operating mode and
physical location within the equipment's operating specification. Equipment
is tested under the most adverse actual or simulated conditions permitted in
the installation instructions.
Test Method: Testing is performed under worst case normal conditions for
clearances. Equipment will be tested within a five-sided enclosure (open at
the front) with the clearances specified by the installation instructions.
If no clearances are specified, the front of the equipment will be set back
5 cm from the front edge with 5 cm clearance on the rear and 1 cm on the top
and sides. Removable items such as feet will be removed or retained to
provide the worst case normal operating condition.
Test Criteria: Temperature rises for internal components and external
surfaces shall comply with the standard taking into consideration operation
at the maximum specified ambient temperature.
Abnormal operating and fault test conditions: Testing is performed under
foreseeable abnormal operating conditions including misuse and under
internal fault conditions. One fault is applied at a time.
Test Method: All openings shall be covered with cheesecloth. The equipment
shall be operated under normal operating conditions except ventilation
faults are applied one at a time including blocked openings (one side at a
time) and locked fan rotor. Openings are blocked with tape if the surface is
flat; otherwise, cloth or plastic wrap shall be used. However, wood shall be
used if it is obvious that the equipment is intended for installation areas
where it is highly unlikely that the ventilation openings will be
accidentally covered by cloth, plastic bags or similar flexible materials.
Test Criteria: Temperature rises for internal components and external
surfaces shall comply with the standard taking into consideration operation
at the maximum specified ambient temperature. Surface temperatures shall not
exceed 100 C. No internal fires shall occur unless it is highly unlikely
that the fire would escape the enclosure. Any internal fire shall
self-extinguish within 30 seconds. If an internal fire occurs, the test
shall be repeated twice with a repaired unit or additional samples.
Markings: If clearances are necessary to comply with the requirements in
this document, the equipment shall be marked with the ISO attention symbol
(ISO 7000-0434). The symbol shall be located on each side of the equipment
where restricted ventilation would cause the equipment to be non-compliant.
Installation and User Instructions: The installation and user instructions
shall prominently state the restrictions for mounting and use including
clearances for ventilation. Consideration shall be given to mounting
location (wall, corner etc.) including orientation. A warning statement
shall be included in the installation instructions drawing attention to the
risk of fire if the equipment is not installed according to the
instructions. A warning statement shall be included in the user instructions
drawing attention to the risk of fire if ventilation openings are
restricted. All user instructions required by this document shall be in the
official language(s) of the country where the equipment is intended to be
sold.
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