Hi all, With dual power cords think: 1. Single fault scenario and how much current will then go through each cord or a single cord if there is a failure of some sort. This is a design thing, easier with two power supplies then splitting the input. 2. Limits to the current on the branch circuit. This can be overcome by stipulating that the power cords have to go to different circuits (and mean it) Regards, Scott
"Pettit, Ghery" <[email protected]> wrote: I've seen this done on server class computers before. Two power supplies, each with its own cord. I'm not a safety engineer (just EMC), but I seem to recall the need for a sticker reminding anyone opening the chassis that there was more than one source of AC power feeding the product. Ghery Pettit From: [email protected] [mailto:[email protected]] On Behalf Of Scott Douglas Sent: Friday, May 04, 2007 9:51 PM To: 'EMC PSTC' Subject: Dual Power Cords on Single Product Hi All, There is a product being safety tested to UL 60065 for NRTL approval for US and Canada. The "normal operating" current is 19.88 amps at 132 VAC. The safety agency says we cannot use a 20 A line cord to power the product because 15.1.1 says the attachment plug shall be rated no lower than 125% of the "normal operating" current. I use the quotes because "normal operating" is a set of conditions specified by the standard. It is not where the product will normally operate; the specified conditions are somewhat artificial to make all products of the type have the same test conditions. The first choice to address the limitation imposed by 15.1.1 would be to go to a 30 A power cord. Unfortunately, marketing types say that will not sell. What they really want is a 15 A cord instead. So a solution is proposed. Divide the product's electronics in two parts and use two power cords to supply the product. The design is such that this is actually a minor change as most of the parts needed are already there. Just add a second inlet, circuit breaker, and control PCB. This then will basically cut the current drawn in half (or actually 57% and 43%). In this condition, one power cord will supply about 11.4 A and the other about 8.6 A. Both of those numbers are less than the 12 A allowed for a 15 A attachment plug thus satisfying 15.1.1. In discussion with our safety lab (one of the big three), this seems like a viable option. But a sister company's safety engineer discussed this with his safety lab (second of the big three) and he was told that they will not do approvals on a product with dual power cords. When pressed he was told this was a decision reached between this agency and another agency (the third of the big three). One of those unofficially official rules. My reading of UL 6500, UL 60065, and EN 60065 does not turn up any prohibitions against two power cords on a single product. I am also not aware of any restriction placed by the US or Canadian National Electrical Codes. So the question is, are there any rules preventing dual power cords on a single product? Both would use NEMA 5-15P 15 A plugs. Are there any gotcha's we need to be aware of? What am I missing? As always, thank you in advance for sharing your expertise. Scott Douglas [email protected] - 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 message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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