Hi Bob: As I said, been there, done that. Look at it this way. Openings in the sides are permitted IF they are related to the ingress of foreign objects with respect to the circuits below the openings. If there are no openings or circuits below the openings, then you still need a side. I know, this is poor rationale. But, you need a side, and it needs to be in proximity to the circuits. Here's my story: Consider a printer with an opening in front for paper input and paper output. The main PWB is vertically-oriented on one side of the opening. The components are on the PWB side facing the opening. The PWB was supplied with SELV, but not LPS. So, a fire enclosure was required. The design included a fire enclosure bottom, a fire enclosure top, a fire enclosure side (non-component side of the PWB), but no enclosure for the component side of the PWB except for the opposite side of the printer. With a great deal of contortion, some of the components were accessible through the front opening. Clearly, nothing could fall onto the circuits through the front opening of the printer. My favorite certification house would not accept the opposite side of the printer as an enclosure for the component side of the PWB. The opposite side was probably 12 inches away from the PWB. Nor would they accept the front opening as complying with the fire enclosure side opening requirements. I'm not arguing with your interpretation of the side opening requirements. I am advising that you cannot win with a certification house that no side is required. Best regards, Rich
From: Robert Johnson [mailto:[email protected]] Sent: Saturday, June 02, 2007 8:19 PM To: [email protected] Cc: 'ieee' Subject: Re: IEC 60950 fire enclosure openings My attempt to put aside the access rules got in the way of the question. Another way of putting it is, if you have a solid top which overhangs the bottom by the 5 degrees, there is no limit to the size of the side opening. It appears the opening can be the size of the side. In other words, is there some undeclared maximum to dimension L in Figure 4D? Bob [email protected] wrote: Hi Bob: Been there, done that. Regardless whether the requirements for side and top openings APPEAR from the text to be for prevention of electric shock, they also apply to fire enclosures. The way the standard is written, the text appears to not require a fire enclosure for the sides and top. Clearly, this is an oversight in the writing of the standard. If you submit the construction for certification, you will find that the cert house will impose the side and top opening requirements. Or... you can perform the fault-all-components test and qualify the construction as not needing a fire enclosure. This was my solution. Best regards, Rich From: [email protected] [mailto:[email protected]] On Behalf Of Robert Johnson Sent: Friday, June 01, 2007 6:18 PM To: ieee Subject: IEC 60950 fire enclosure openings I have come up with a question and will try to strip it to its essentials. Consider a part which requires a fire enclosure, as a hypothetical example a primary rectifier bridge with reinforced insulation. It is safe to touch, with no live parts, so top openings or side access is not restricted. A bottom enclosure is provided out beyond the 5ยบ projection. The question is what is the fire enclosure? Clause 4.6.1 places no limits on side or top openings since access is not an issue. In fact it appears the opening can extend from the bottom up the sides and over the top and down the other side to the bottom. Is it necessary for a fire enclosure to envelope the part? The next difficult question is what is a part placed in this opening? If parts are placed in the opening (anywhere beside or above the part requiring the fire enclosure), they must be V-1 (etc. see 4.7.3.2), but if outside the opening they may be HB (etc. see 4.7.3.3). No distance is specified, so in my case it appears a plastic window 12 inches away appears to be occupying an opening in an enclosure. I can apply 4.7.1 method 2, but do the enclosure requirements of method 1 fail to be usable in this situation? Any opinions? Robert Johnson ITE Safety - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
