This reply is a personal opinion and does not represent the views of my employer.
Ground lift switches do not affect the protective ground electrical connection between the AC third wire and the equipment chassis. Ground lift switches separate the audio input and/or output shield connection from the protective ground. I hope that this distinction makes it clear that a ground lift link or switch is not an electrical hazard. Ground lift switches and links are common on pro-audio equipment to facilitate the task of the quality conscious installer who has to deliver a system free of hum and RF pick-up to his customer. Remember the Spinal Tap gig at the Airbase? Voice communications between tower and pilot coming through loud and clear on the stage amplifiers? Ground everything once and you're OK. Ground stuff a second time via the audio cable shields and you have a problem. The cc recipient of the original message has the company name of a major UK based professional audio sound console company 'CADAC' with installations the world over. I expect they are already aware of the difference between audio ground lifting and protective ground lifting. It is necessary to distinguish lest confusion spreads. >> <[email protected]> 20-Mar-02 11:59:19 AM >>> Dear Group Does anyone know if it is legally permissible in the USA to remove the safety grounds from Class I equipment used in pro-audio systems and installations? It has been a common practice over many many years in professional audio systems and installations to 'lift the grounds' on equipment to cure hum problems. I'm comfortable with the knowledge that in Europe it is a breach of the Low Voltage Directive to supply equipment that is constructed using Class I methods if its protective ground conductor is not connected, or if it could be 'lifted' by operation of a user-accessible switch or jumper. I am also comfortable with the idea that in Europe if the user does not connect a protective ground conductor to Class I equipment, the health and safety at work directives mean that he/she is probably committing a criminal act. A Health and Safety Inspector could close down his/her facility if he/she discovered such an error. My question concerns the comparable situation in the USA. I am under the impression that my summary above for European protective grounding requirements for Class I equipment also applies to the US, both for the supply of the equipment and the installation of systems using it. But I am reliably told that there are a great many pro-audio products, systems, and installations in the USA where protective grounding is treated as just a hum control measure and safety issues take second place. I am also reliably told that in the US one can even find whole buildings wired using two-core mains cables, without any safety ground wires to any of the pro-audio equipment. So what are your views on removing the safety grounds from Class I equipment used in pro-audio systems and installations? Can anyone defend this practice or show that it is legal in the USA? All the very best Keith Armstrong Note: Class I equipment uses basic insulation plus protective ground bonding to protect against electrical hazards, and must use three-pin mains connectors and three-core mains leads (for single-phase supplies). The only alternative permitted (in Europe, anyway) for mains-powered equipment is Class II - 'double insulation' . This must have no protective ground conductor and must use two-pin mains connectors and two-core mains leads (again, for single phase supplies). Best Regards Ted Rook, Console Engineering, ext 4659 Please note our new location and phone numbers: Crest Audio Inc, 16-00 Pollitt Drive Fair Lawn, NJ 07410 USA 201 475 4600 telephone receptionist, 8.30 - 5 pm EST. 201 475 4659 direct line w/voice mail, 24 hrs. 201 475 4677 fax, 24 hrs. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
