Thank you John and Dennis your input it is greatly appreciated ! Reg Henry
From: John Barnes [mailto:jrbar...@iglou.com] Sent: Wednesday, December 16, 2009 8:07 PM To: emc-p...@ieee.org; Reginald Henry Subject: Re: FCC PERSONAL COMPUTERS FOR COMMERICAL ENVIORMENT Reginald, > Now I think that I understand.. so there is limited testing to be done > by the assembler in terms of mother board and power supply with the > chassis open covered.. and testing must be performed at > an independent labs If the assembler changes to another PS or MB the > test must be redone ? Dennis Ward's E-mail talked about the record-keeping issues, and my previous E-mail talked about the technical issues, of assembling personal computers (PC's) from approved motherboards and power supplies. If you abide by these rules, you-- as a personal-computer manufacturer-- do not have to do *any* electromagnetic compatibility (EMC) testing at all! You can mix and match power supplies, motherboards, cases, and other goodies to your heart's content, without getting an EMC test lab involved-- for sales in the United States. Unless, of course, your product causes interference problems (FCC 47 CFR Part 15, 15.102(b)(5)), in which case you are on the hook big-time. If a manufacturer makes a motherboard that meets FCC47 CFR Part 15 Paragraph 15.32(a)(1), or a power supply that meets Paragraph 15.32(b), they will brag about "meeting FCC Part 15" in their: * Advertizing, * Catalogs, * Web pages, * Data sheets, and * On the boxes, because this is a major selling point for them. Of course, just because a manufacturer claims something, does not necessarily mean that it is true. If you have never heard of the manufacturer, and their prices seem too good to be true, you may want to ask around, and get-- and carefully study-- copies of their Declarations of Conformity (DoC's), safety certificates, etc. before you place any large orders with them. In a personal computer (PC), the power supply usually generates the worst Conducted Emissions, and the motherboard the worst Radiated Emissions. Everything else that we stuff into a computer tends to be relatively quiet compared to these two components. A good case can significantly reduce Radiated Emissions, and can reduce Conducted Emissions somewhat. In the 1980's/early 1990's the computer industry was pushing the FCC to let them assemble personal computers without having to put every variant through long, extensive (and expensive) electromagnetic compatibility (EMC) tests. A major consideration, then and now, is that users can easily customize/upgrade personal computers to meet their needs-- and they had been doing so for some time without causing major interference problems. So why were computer manufacturers being given such a huge handicap? The FCC came up with the rules in FCC 47 CFR Part 15 that I discussed in my previous E-mail, basically providing that: * If you have a quiet power supply, the case doesn't matter. * If you have a quiet motherboard, the case doesn't matter. * But if the power supply OR motherboard is noisy, it must be provided with a good case to limit the Conducted and Radiated Emissions. Thus a power supply/motherboard manufacturer can: * Scrimp on development time and cost, and manufacturing cost, to make cheap power supplies/motherboards that can only be sold to high-volume manufacturers with strong EMC expertise. * Spend more development time and cost, making more expensive power supplies/motherboards that can be sold to anyone. High-volume PC manufacturer can buy the cheap power supplies and motherboards, put them in inexpensive cases, and do the development work themselves to meet FCC Part 15 at the lowest-possible total manufacturing cost. The additional engineering time/cost and EMC testing get amortized over many units, so they aren't a big burden. Low-volume PC manufacturers (garage shops) can buy the better power supplies/motherboards, slap them together in any cases that customers want (even for individual custom PC's), and ship them. Users can buy anything from a mass-produced off-the-shelf PC, to a fully custom one that they assemble at home, and anywhere in between. John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE dBi Corporation http://www.dbicorporation.com/ CONFIDENTIALITY NOTICE: This transmission may contain information that is privileged, confidential and/or exempt from disclosure under applicable law. If you are not the intended recipient, you are hereby notified that any disclosure, copying, distribution, or use of the information contained herein (including any reliance thereof) is strictly prohibited. If you receive this transmission in error, please immediately contact the sender and destroy the material in it's entirety,whether in electronic or hard copy format. The views expressed in this communication may not necessarily be the views held by the company. Thank you. 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