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, [email protected] writes: > Subj:RES: Pro-audio and ground lifting > Date:20/03/02 17:45:50 GMT Standard Time > From: [email protected] (SERGIO LUIZ DA ROCHA LOURES) > To: [email protected], [email protected] > CC: [email protected] > >> >> 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: [email protected] >> >> Minha opinião e não necessariamente a do meu empregador. >> >> >> -----Mensagem original----- >> De: [email protected] [mailto:[email protected]] >> Enviada em: quarta-feira, 20 de março de 2002 13:59 >> Para: [email protected] >> Cc: [email protected] >> 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).
