Re: Shielded power cord, seeking source for
Hi Tim. You wrote: If screened mains cable is used, then surly it acts like a coax (a poor one possibly) and transfers the energy, contained within, to a point where the cables are not shielded. This would probably be at the mains wall socket - where the energy could (would?) then radiate! If the intention is not to cause interference to radiocommunications etc. then how has the screened mains cable helped? The test might seem OK but how is due diligence served? My problems have been that filters are often guilty of resonances at particular frequencies, providing substantial gain rather than attenuation. With 'white noise' things like phase angle controllers in the box, these filters put (in one instance) 32MHz out on to the mains cable, which radiated beautifully. The screen was sufficient to drop those emissions by about 15dB, thereby bringing it back into compliance. The transmission line characteristics of screened three core cable are very poor, and the conducted emissions of the 32MHz past the mains lead were clearly very much reduced by the inductance/capacitance of the cable, in that the -15dB results were perceived. The radiated emissions included those from the mains supply to the equipment. The mains cable on this thing was 3 metres long, and made up from component's, not moulded. The screen was grounded at the Supply end. Interesting stuff... Chris Dupres Surrey, UK.
RE: Shielded power cord, seeking source for
Hi Rick. You wrote: It is my understanding that shielded power cords are not allowed on products in European markets. As I recall, the rationale is that if a cord is replaced, there is no guarantee that it can, or will, be replaced with a shielded cord. Not as far as I am aware, and I have been designing mains powered stuff since I was too young to know better... But then I'm not aware of any manufacturers of Moulded Screened Mains Cable assemblies, they are invariably home made. Screened mains cable is freely available on the reel (in the UK from people like RS Components for instance) and I have used it when I have had problems with radiated emissions or susceptibility on long mains cables. Usually when a filter demonstrates a particularly arkward resonance. Any component which is safety or EMC critical, and which may be changed by a subsequent user can be made a condition of compliance by a relatively simple statement in the instructions. i.e. under the general heading of 'Using as intended'. Use of the equipment without the particular cable is therefore 'Not as intended' and therefore shouldn't be expected to comply (and shouldn't be put into service). A thruppence worth perhaps. Chris Dupres Surrey, UK.
RE: Shielded power cord, seeking source for
It is my understanding that shielded power cords are not allowed on products in European markets. As I recall, the rationale is that if a cord is replaced, there is no guarantee that it can, or will, be replaced with a shielded cord. -Original Message- From: Bob Blank [SMTP:bbl...@us.bnsmc.com] Sent: Thursday, January 22, 1998 12:24 PM To: emc-p...@ieee.org Subject:Shielded power cord, seeking source for Seeking source for shielded power cords to meet CE mark requirements. Prefer braided shield (80% tinned copper) instead of foil 18/3, CEE color coding, 10A, 125 V, PVC jacket, 9'10 long should have female connector PH-30 (angled IEC 320) molded on Should meet any other specs required for CE mark Any advice is greatly appreciated R. Blank
