Re: Pro Audio and ground lifting
There are a couple of very different "real life" issues here. If you have volunteered to be in charge of sound for a choir concert at your local church, and it's fifteen minutes to showtime, and you've got hum in the PA system, you will doubtless pull every rabbit out of every hat you can think of. One rabbit may be floating a shield on the end of a cable. Forget EMC. Forget safety. The show goes on. But, short of fear-driven panic patches, it is almost appropriate to float shields on cables. Disconnect a shield on one end of a cable and you have transformed it into an efficient monopole antenna. It will be susceptible to inbound RF, and it will transmit RF very nicely in the same manner. A bad idea. At the lab, we work with several Pro-Audio clients who manufacture high-performance equipment. Shield floating is just not done. It is not necessary ... if the overall product design is well thought out. And yes, I do understand the reality of fighting hum problems in a crisis situation. In a previous life, I was Chief Engineer for several commercial radio and TV broadcast outlets. In situations (particularly setting up remote broadcasts with unknown equipment), anything goes. But we shouldn't carry that behavior back to the design teams. My comments may or may not reflect the opinion of my employer. Regards, Jim Ericson Senior EMC Engineer Acme Testing Company Acme, WA. work e-mail: j...@acmetesting.com --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
Re: Pro-audio and ground lifting
Dear Mike I'm sure professionals like yourself wouldn't dream of ever cutting a safety ground. Yet it does happen in pro-audio and video installations, even sometimes in the Albert Hall in London at black tie concerts. I know the US doesn't have laws equivalent to Europe's LVD, but I didn't know whether the actions of OSHA and similar bodies had a similar effect to the LVD. All the very best! Keith Armstrong In a message dated 20/03/02 20:04:01 GMT Standard Time, mertino...@skyskan.com writes: > Subj:RE: Pro-audio and ground lifting > Date:20/03/02 20:04:01 GMT Standard Time > From:mertino...@skyskan.com (Michael Mertinooke) > Reply-to: mailto:mertino...@skyskan.com";>mertino...@skyskan.com > To:cherryclo...@aol.com > > Hi; > > What the heck is a "Class I location"? > > I'm serious. There are about forty-eleven different standards, > each of which seems to have created something called > Class I, Class II, and Class III locations. For example, the > US National Electrical Code classifies Class I Locations > (Section 500-7) as "Those in which flammable gases or > vapors are or may be present in the air in quantities ..." > and so forth. > > By the way, you are not going to get anybody to approve > removing a protective ground wire in a hazardous location. > > Judging from the note at the bottom of your email, I > think you mean UL Class I apparatus. This is equipment in > which protection against shock requires connection of accessible > conductive parts to the protective conductor (per UL6500 > section 2.38). > > If so, then you already have your answer. Protection against > electric shock REQUIRES that the conductive parts be connected > to Earth at all times. You may not, never, nohow go > around cutting no ground wires, okay? > > >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. > >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? > > The hell you say! It is most certainly NOT legal, and is > NOT common practice to remove ANY protective grounds! > > What is common practice in Audio equipment is to provide > a "functional earth" or a "reference earth" ground terminal. > And yes, it is extremely common to provide this option. > In fact, a shielded audio cable almost never works right > unless you float the shield at one end. This is perfectly > acceptable, because the Protective Earth ground connection > remains intact at all times. > > Okay, so I do not doubt you have had some clowns try to > tell you to snip the Safety ground. *sigh* professional audio > seems to be where children go when they want to pretend > to be engineers. But don't judge us by these morons, okay? > > See ya. > Mike Mertinooke >
Re: Pro-audio and ground lifting
Dear Ken Thank you for your reply. I am sure that most installers know what they are supposed to do for electrical safety, but some seem very ready to cut safety corners when hum appears in the audio signal. This is a worldwide problem in pro-audio installations, of course, not a specifically US one. The answers I was hoping to discover are also popping up in the thread "NEC Question". I think I am learning that in the US, safety measures are more likely to be taken to please insurers, or out of fear of litigation after a safety incident, than they are likely to be taken as result of safety legislation such as the European LVD. All the very best! Keith Armstrong In a message dated 20/03/02 18:55:51 GMT Standard Time, ken.ja...@emccompliance.com writes: > Subj:Re: Pro-audio and ground lifting > Date:20/03/02 18:55:51 GMT Standard Time > From:ken.ja...@emccompliance.com (Ken Javor) > Sender:owner-emc-p...@majordomo.ieee.org > Reply-to: HREF="mailto:ken.ja...@emccompliance.com";>ken.ja...@emccompliance.com > (Ken Javor) > To:cherryclo...@aol.com, emc-p...@ieee.org > CC:t...@cadac-sound.com > > Building wiring is such that separate mains and grounds are provided for > audio power and lighting power. Mics are provided with above ground > circuits so that mic output is immune from ground noise. All pro-audio > gear is provided a case ground green wire and that is not defeated. The > above related to me by an EMC engineer who used to work as a roadie. > > -- > From: cherryclo...@aol.com > To: emc-p...@ieee.org > Cc: t...@cadac-sound.com > Subject: Pro-audio and ground lifting > Date: Wed, Mar 20, 2002, 10:59 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). >>
Re: Pro-audio and ground lifting
I read in !emc-pstc that Chris Maxwell wrote (in <83d652574e7af740873674f9fc12dbaaf7e...@utexh1w2.gnnettest.com>) about 'Pro-audio and ground lifting', on Wed, 20 Mar 2002: >I have a feeling that >"hum" could be solved by power filtering without disconnecting grounds; >the ground removal is probably just an easy way out. Power filtering is rarely the problem. The main cause of hum is circulating currents in signal and protective grounds. This is why disconnecting the protective ground 'cures' the problem. The correct way to cure it is to use balanced signal circuits, or at least balanced inputs. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
Re: Pro-audio and ground lifting
I read in !emc-pstc that Ted Rook wrote (in ) about 'Pro-audio and ground lifting', on Wed, 20 Mar 2002: >Ground lift switches do not affect the protective ground electrical connection >between the AC third wire and the equipment chassis. The trouble is that the term 'ground lift' is used both for disconnecting the protective conductor and for separating the protective and audio 'grounds'. The OP clearly asked about the former action. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
RE: Pro-audio and ground lifting
Well, What's legal? What's smart? What gets by unnoticed? What is practical? What's legal: If a product is Class 1 (needs Earth Ground) then legally it needs to have its ground conductor plugged in. That's regardless of if it's the US, UK, U(anywhere).I say "legally" in the sense that you are violating UL, OSHA, (the authority having jurisdiction) the manufacturer's instructions... The penalty depends upon who inspects your facility. It also depends on who you are. For instance, we unground oscilloscopes on a regular basis when conducting noise measurements on sensitive circuitry. But, we're engineers, we know the risks. We do it of our own free will. We are "professionals" trained to deal with risks that the general public shouldn't be exposed to. What's smart: It's always smart to ground Class 1 equipment.I have a feeling that "hum" could be solved by power filtering without disconnecting grounds; the ground removal is probably just an easy way out. What gets by unnoticed: You may have heard about buildings with no ground because there are a ton of them here in the states. Many of them go unnoticed because the Authority having Jurisdiction hasn't had an excuse to inspect them. For instance, my own house is almost entirely ungrounded; I don't get any greif because it hasn't changed ownership (no mortgage loan inspection) and it hasn't been remodeled (no building permits applied for)...so it hasn't been inspected. Theoretically, I could put a professional audio system in my house without grounding it and nobody would know. OSHA wouldn't inspect it because I'm not an employer. --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
Re: Pro-audio and ground lifting
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: mailto:t...@crestaudio.com";>t...@crestaudio.com (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. > > > > >> 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
Re: Pro-audio and ground lifting
Dear John I was aware of the ability to mix Class I and II construction in a single product, but as I understand it such a product must be treated as if were simply Class I, in that it must have a protective ground connection via its power cord. I was sure that the AES would not condone removing the safety ground connection where it is needed for safety, and am pleased that you have confirmed that this is the case. All the very best! Keith Armstrong www.cherryclough.com In a message dated 20/03/02 19:19:04 GMT Standard Time, j...@jmwa.demon.co.uk writes: > Subj:Re: Pro-audio and ground lifting > Date:20/03/02 19:19:04 GMT Standard Time > From:j...@jmwa.demon.co.uk (John Woodgate) > Sender:owner-emc-p...@majordomo.ieee.org > Reply-to: mailto:j...@jmwa.demon.co.uk";>j...@jmwa.demon.co.uk > (John Woodgate) > To:emc-p...@majordomo.ieee.org > > I read in !emc-pstc that cherryclo...@aol.com wrote (in <17d.557eff5.29c > a1...@aol.com>) about 'Pro-audio and ground lifting', on Wed, 20 Mar > 2002: > >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). > > This is true for consumer products but for professional audio equipment > under IEC/EN60065, an arrangement whereby *parts* of the product meet > Class II requirements while other parts meet Class I requirements has > been accepted by Notified Bodies for some years. These can be shown to > be just as safe as conventional products. > > With regard to your main enquiry, professional audio engineers in the > Audio Engineering Society are severely critical of 'ground lift' > solutions. The correct, and safe, solutions, lie in the signal circuits > that sustain the ground loops. The subject is extensively treated in the > June 1995 issue of the Journal of the Audio Engineering Society. > -- > Regards, John Woodgate, OOO - Own Opinions Only. > http://www.jmwa.demon.co.uk > Interested in professional sound reinforcement and distribution? Then go to > http://www.isce.org.uk > PLEASE do NOT copy news posts to me by E-MAIL! >
Re: Pro-audio and ground lifting
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. >> 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
Re: RES: Pro-audio and ground lifting
Dear Sergio Many thanks for replying. I have no problems with switches such as you describe, and have used them myself. It is switches that disconnect the protective earth, which I have also seen (plus just plain disconnecting the green/yellow wire) that I am concerned about. All the very best! Keith In a message dated 20/03/02 17:45:50 GMT Standard Time, sergioro...@siemens.com.br writes: > Subj:RES: Pro-audio and ground lifting > Date:20/03/02 17:45:50 GMT Standard Time > From:sergioro...@siemens.com.br (SERGIO LUIZ DA ROCHA LOURES) > To:cherryclo...@aol.com, emc-p...@ieee.org > CC:t...@cadac-sound.com > >> >> keith, >> >> In pro-audio systems, normally you found a ground lift switch. This switch >> disconnects the signal shield from the equipment ground. It doesn’t >> disconnect the protection earth from the main supply. >> >> Regards >> >> Sérgio L. Rocha Loures >> Siemens Ltda. - Brazil >> Supply Chain - Quality and Engineering >> IC SC QE L >> Tel: +55 41 341-5898 >> Fax: +55 41 341-5058 >> E-mail: sergioro...@siemens.com.br >> >> Minha opinião e não necessariamente a do meu empregador. >> >> >> -Mensagem original- >> De: cherryclo...@aol.com [mailto:cherryclo...@aol.com] >> Enviada em: quarta-feira, 20 de março de 2002 13:59 >> Para: emc-p...@ieee.org >> Cc: t...@cadac-sound.com >> Assunto: Pro-audio and ground lifting >> >> >> 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).
Re: Pro-audio and ground lifting
I read in !emc-pstc that cherryclo...@aol.com wrote (in <17d.557eff5.29c a1...@aol.com>) about 'Pro-audio and ground lifting', on Wed, 20 Mar 2002: >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). This is true for consumer products but for professional audio equipment under IEC/EN60065, an arrangement whereby *parts* of the product meet Class II requirements while other parts meet Class I requirements has been accepted by Notified Bodies for some years. These can be shown to be just as safe as conventional products. With regard to your main enquiry, professional audio engineers in the Audio Engineering Society are severely critical of 'ground lift' solutions. The correct, and safe, solutions, lie in the signal circuits that sustain the ground loops. The subject is extensively treated in the June 1995 issue of the Journal of the Audio Engineering Society. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
Re: Pro-audio and ground lifting
Building wiring is such that separate mains and grounds are provided for audio power and lighting power. Mics are provided with above ground circuits so that mic output is immune from ground noise. All pro-audio gear is provided a case ground green wire and that is not defeated. The above related to me by an EMC engineer who used to work as a roadie. -- From: cherryclo...@aol.com To: emc-p...@ieee.org Cc: t...@cadac-sound.com Subject: Pro-audio and ground lifting List-Post: emc-pstc@listserv.ieee.org Date: Wed, Mar 20, 2002, 10:59 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).
RES: Pro-audio and ground lifting
keith, In pro-audio systems, normally you found a ground lift switch. This switch disconnects the signal shield from the equipment ground. It doesn't disconnect the protection earth from the main supply. Regards Sérgio L. Rocha Loures Siemens Ltda. - Brazil Supply Chain - Quality and Engineering IC SC QE L Tel: +55 41 341-5898 Fax: +55 41 341-5058 E-mail: sergioro...@siemens.com.br Minha opinião e não necessariamente a do meu empregador. -Mensagem original- De: cherryclo...@aol.com [mailto:cherryclo...@aol.com] Enviada em: quarta-feira, 20 de março de 2002 13:59 Para: emc-p...@ieee.org Cc: t...@cadac-sound.com Assunto: Pro-audio and ground lifting 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).
Pro-audio and ground lifting
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).
