Hi Peter:
> 1. Per UL1950/EN60950 can any capacitor be used to bridge basic
> insulation between a TNV-3 circuit and a SELV circuit or should it
> be a Recognized/Certified Y-capacitor?
No.
By definition, only a Y capacitor is considered basic
insulation. All other capacitors are considered
operational insulation.
> 2. Can the insulation over an electrolytic capacitor be considered
> as insulation when evaluating spacings? One North American test
> lab refused to consider the insulation over the capacitor since
> "there is no control (traceability) over the material used to insulate
> the capacitor".
Depends.
If the plastic covering is to be considered a basic,
supplementary, or reinforced insulation (which are the
only insulations that need be considered for safety
purposes), then it must be rated as insulation and
tested appropriately for at least electric strength and
temperature stability.
In the absence of such ratings, then the insulation must
be considered as operational insulation, and would not
be taken into consideration when evaluating spacings.
> However, after showing them competitors' products
> with their own test mark applied and where the plastic covering over
> electrolytic capacitors was used to provide basic insulation
> between the metal can and the earthed heat sink, the test lab
> accepted our customer's construction. What is the group's opinion?
Some certification houses may require safety insulations
to be certified insulations.
> 3. Many times when we have tested power supplies for abnormals,
> electrolytic capacitors vented and emitted smoke. Under these
> conditions, our test lab usually is covered up with heavy smoke
> (reminds me of the fog in the Bay Area!) and the lab technicians
> are wearing "gas masks" (reminds me of the Gulf War!). We then
> applied the compliance criteria for the Abnormal Tests including
> Dielectric and Leakage Current Tests and found the power supplies
> fully compliant.
Agree.
But, capacitor venting is NOT smoke. It is the hot, fluid,
steam-like electrolyte.
Smoke is the result of pyrolysis, the decomposition of a
material by heat alone.
> What does the group think about smoke being emitted from
> equipment during Abnormal Testing? Should there be a standard
> requirement to measure the toxicity of the fumes?
There are two questions here:
1) Is smoke an acceptable result of an abnormal test?
2) If smoke is emitted, should it comply with toxity
requirements?
Smoke is a necessary precursor to fire. But, the presence
of smoke does not mean a fire is imminent. The source of
the smoke should be evaluated to determine if fire is
imminent or not. If fire is imminent, then the product is
not acceptably safe.
All smoke is toxic -- provided the concentration is
sufficient. The concentration will depend on the size of
the room in which the equipment is located when it smokes.
All smoke contains CO, which is toxic. Most fire deaths
are due to smoke inhalation, where the toxic material is
CO. Smoke may also contain other toxic materials, but
the principal toxic material is CO.
Customers, of course, are VERY unhappy whenever a product
emits smoke. Its very hard to explain to a customer why
smoke is an acceptable result of a fault.
Best regards,
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 619 655 3329
16399 West Bernardo Drive FAX : +1 619 655 4979
San Diego, California 92127 e-mail: [email protected]
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