Dear Ted OK, OK, after two postings making much the same point maybe I should have been more careful to make it clear that I was only worried about the kind of "ground lift switches" which disconnect the protective ground from the chassis of the equipment. I have seen them used in pro-audio equipment in the past.
It is also a traditional bad habit in the pro-audio business to remove the protective conductor connection from the mains plug or the chassis if it helps cure a hum. I am trying to see if there is anyone out there who will make a case for such unsafe practices, or point me to US regulations or standards of codes of practice that permit it. All the very best! Keith Armstrong www.cherryclough.com In a message dated 20/03/02 20:01:41 GMT Standard Time, t...@crestaudio.com writes: > Subj:Re: Pro-audio and ground lifting > Date:20/03/02 20:01:41 GMT Standard Time > From: t...@crestaudio.com (Ted Rook) > Sender: owner-emc-p...@majordomo.ieee.org > Reply-to: <A HREF="mailto:t...@crestaudio.com";>t...@crestaudio.com</A> (Ted > Rook) > > X-INFO: INVALID TO LINE > > 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. > > > > >> <cherryclo...@aol.com> 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. >
