Rich suggested testing the standoff for flammability, then showing the inspector that you are indeed using the same standoff as tested when a factory inspection is performed. This route would make me uncomfortable for a few reasons: 1. It may not pass, 2. Standoffs are a very cheap commodity, and for manufacturing reasons, you wouldn't want to be limited to a single source for this part, 3. you would need to get CofC's from the vendor with each shipment to show continuing compliance at every factory inspection, and 3. Added cost to your product evaluation for flame tests.
As Richard Woods pointed out, if the electrical parts (PCB traces) cannot produce a temperature under fault that would cause ignition, then the part can be considered exempt from the V-2 or better requirement. I would suggest doing a fault analysis of the circuit to detirmine what fault could be applied to the circuit to create maximum current through the circuit traces, apply the fault, measure heat rise on the trace, then make a case for engineering judgement to be applied by the project engineer. The test lab will want to perform the tests themselves, of course, but if you provide a good analysis to them for verification, you'll have better luck getting the call on your side. Doug Massey LXE, Inc. -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Tuesday, February 20, 2001 12:48 PM To: [email protected] Subject: RE: FLAME RATING OF STANDOFFS Rich said "The small-part exemption cited by Terry only applies to small parts separated from electrical parts by at least 13 mm (1/2-inch) of air." Actually, the 13 mm separation only applies for small parts near electrical parts "which under fault conditions are likely to produce a temperature that could cause ignition." Thus, small parts can be accepted even if they are close to electrical parts as long as fault testing demonstrates that the small parts cannot catch fire. Richard Woods ---------- From: Rich Nute [SMTP:[email protected]] Sent: Tuesday, February 20, 2001 11:45 AM To: [email protected] Cc: [email protected]; [email protected] Subject: Re: FLAME RATING OF STANDOFFS Hi Kazimier and Terry: Kazimier suggests asking the question: "what's the safety concern" Unfortunately, safety certification houses do not have the option of accepting products based on the answer to this question. A safety certification house certifies a product to a standard. Supposedly, the requirements contained in the standard make the product safe. In this case, IEC 60950, Sub-clause 4.4.3.2 requires all materials and components be rated V-2 or better. So, the certification house is requiring that the construction comply with the standard. You can't fault the certification house for imposing a requirement explicitly stated in the standard. The small-part exemption cited by Terry only applies to small parts separated from electrical parts by at least 13 mm (1/2-inch) of air. I would guess, from Terry's description and the action of the certification house, that this is not the case. (If it is the case, then you can invoke this sub-clause and the matter is closed.) Fortunately, the standard provides an option of testing. If you test the stand-off for flammability and it is flame-retardant, then your construction is acceptable. Now, instead of proving to the inspector that the material is V-2, you need only prove to the inspector that the stand-off is the manufacturer and "model" number that was tested. If you can't do this, then there is still another test option. You can test a non-flame- retardant standoff. If the resulting fire does not spread within the equipment, then you have proved that the standoff is indeed inconsequential to any fire. If you prove this, then there is no need to control the material. Best regards, Rich ps: Being a long-time certification house basher, I can't believe I've written a message defending a certification house! > Hi Terry, > > Sounds like a discussion with your agency safety engineer might be in order. > It's certain there's a line of reasoning behind the "new" approach taken by > the agency, that you've described below. Question is, since the standard > clauses you've called out make certain allowances, the real issue might > easily be addressed by asking "what's the safety concern"? If the agency > rep. understands your product, your reasoning and it all falls into an area > of interpretation without any blatant standard violations, a certain amount > of engineering judgment might help resolve the situation. > > > My opinion only and not that of my employer. > > Good Luck. > Regards, > Kaz Gawrzyjal > [email protected] > > > -----Original Message----- > From: Terry Meck [mailto:[email protected]] > Sent: Tuesday, February 20, 2001 9:44 AM > To: [email protected] > Subject: FLAME RATING OF STANDOFFS > > > > Hi group! > > I need a sanity check on a `new approach' our safety agency has recently > taken. > > We have an open frame power supply ( has all the certs through the CB report > etc. for EN 60950 UL 1950 ) > > On of the conditions of acceptability is one mounting standoff shall be > insulated. We have this supply in no less then 4 listed products without > any reference to the flame rating of the standoff having to be checked when > the inspector comes in. > I consider that to be reasonable. section 4.4.3.3 UL 1950 has exception: > "gears, cams, belts, bearings and other small parts which would contribute > negligible fuel to a fire;" > > Recently new products have been reviewed and the new procedures require > `traceable 94V-2' standoffs!?!? Which manufacturing engineering says is > difficult to procure a traceable recognized plastic standoff. > > Questions: > Has my fever and pneumonia the past weeks clouded my reasoning? What am I > missing? You place a .5 inch #6 standoff between a V-0 board and a medal > chassis what requires a recognized part except maybe `straining out the > gnats so we can swallow the camel' somewhere else. > > Sick and Tired > Terry J. Meck > Senior Compliance / Test Engineer > Accu-Sort Systems > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
