>---------- >From: Rich Nute[SMTP:[email protected]] >Sent: Monday, October 14, 1996 8:50PM >To: [email protected] >Cc: [email protected] >Subject: Re: Do UL1950 Recognized PS's Need Fire Enclosures > > > >Hello from San Diego: > > >At the urging of a colleague, I looked further into the question >raised by Mike Rains, whether or not a power supply needs to be >in a fire enclosure. > >(I had stated that all primary circuits required a fire enclosure.) > >In IEC 950 and its clones, Sub-clause 4.4.1 specifies two methods >for "achieving resistance to fire." > > Method 1: Construction as specified in Sub-clause 4.4.2 > and 4.4.3. > > Method 2: Fault tests as specified in Sub-clause 5.4.6, > third dashed paragraph. > >Sub-clause 5.4.6 first dashed paragraph requires fault tests in >any components in primary circuits -- REGARDLESS whether the >primary circuit is in a fire enclosure or not. > >The third dashed paragraph implies tests in addition to the >first dashed paragraph, i.e., such as overload. Compliance with >this paragraph, in addition to the first dashed paragraph, >qualifies a circuit and its components for no fire enclosure. > >So, the standard does not require a fire enclosure for a power >supply provided it is tested in accordance with BOTH first and >third dashed paragraphs of Sub-clause 5.4.6. > >>>>This is a different reasoning process than that of Mike Rains.<<< > > >Best regards, >Rich > > > >------------------------------------------------------------- > Richard Nute Quality Department > Hewlett-Packard Company Product Regulations Group > San Diego Division (SDD) Tel : 619 655 3329 > 16399 West Bernardo Drive FAX : 619 655 4979 > San Diego, California 92127 e-mail: [email protected] >-------------------------------------------------------------
Rich, Our reasoning process is the same. I referenced clause 5.4.9, which included, by reference, the first and third dashed paragraphs of 5.4.6. Primary circuit components weren't excluded. The power supply (primary and secondary) is a single printed wiring assembly. The basic question becomes: can we anticipate and design tests to simulate all the abnormal and fault conditions that could start and spread a fire beyond the equipment? Thanks for the time and interest. Best regards. Mike Rains >Foxboro Co. > >
