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:[email protected]] Sent: Tuesday, July 18, 2017 11:47 AM To: [email protected] 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. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.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]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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]>
