I agree that (national) legislation should play a role here, but EMC chambers are NOT ordinary equipments, nor part of a standard electrical installation. I would not rely on electrical codes to create a safe work environment, and have my personal opinions prevail.
We operate in a gray area, where safety is concerned. So here good (low voltage) engineering practice suggests "permanent connection" and due to the specifically lethal character of the "high leakage current device" of the device, a second backup connection is not superfluous. Gert From: John Woodgate [mailto:jmw1...@btinternet.com] Sent: Tuesday 18 July 2017 21:09 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Chamber grounding [General Use] I think the issue is far more about electrical safety than EMC. Of course you are quite right about a Faraday cage not requiring an earth connection. It's what happens if there is a high-current live mains to accessible metal fault. The preferred technique depends on how such a fault is detected and rendered harmless. National electrical codes have much to say about this, and they don't all require the same solutions. That's why I advised the OP to look at BS 7694, because that is what applies in Britain. With best wishes DESIGN IT IN! OOO - Own Opinions Only www.jmwa.demon.co.uk <http://www.jmwa.demon.co.uk/> J M Woodgate and Associates Rayleigh England Sylvae in aeternum manent. From: Ghery S. Pettit [mailto:n6...@comcast.net] Sent: 18 July 2017 19:59 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Chamber grounding [General Use] It's not so much that it needs filtering at the power frequency as it is that that much line to ground capacitance is needed to provide 100 dB of insertion loss down to 10 kHz (which is typical for chamber power filters). Back to the original question - I've had 3 and 10 meter chambers in different places over the years. The first chamber was built before I joined the company and the engineer worked very hard to maintain a single point ground for the chamber. I built a 10 meter chamber for the same company a number of years later and didn't worry about a single point ground. Both worked fine. A Faraday Cage, once you are talking high enough frequencies (and 10 kHz is high enough), doesn't care if it is ungrounded, single point grounded or multi-point grounded. The RF currents flow close enough to the surface that the shield is good. Now, if you have a problem with 60 Hz power causing currents to flow through the shield material you may have a different problem. I've never had to care about shielding effectiveness at 60 Hz, so skin effect hasn't been an issue for me. YMMV. Ghery S. Pettit, NCE From: Richard Nute [mailto:ri...@ieee.org] Sent: Tuesday, July 18, 2017 11:47 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Chamber grounding [General Use] "But as soon as mains filters are mounted on the wall, one has to cope with leakage currents (blind current) as large as 6 amp or more." 6 amps! At 230 volts, 50 Hz, Xc is 38.8 ohms. Total C from line to earth is 69.2 uF! (Presumably the filter has an equal capacitance from neutral to earth.) Why does a chamber need so much filtering at mains frequency? Rich - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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