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, [email protected] writes: > Subj:Re: Pro-audio and ground lifting > Date:20/03/02 18:55:51 GMT Standard Time > From: [email protected] (Ken Javor) > Sender: [email protected] > Reply-to: <A > HREF="mailto:[email protected]";>[email protected]</A> > (Ken Javor) > To: [email protected], [email protected] > CC: [email protected] > > 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: [email protected] > To: [email protected] > Cc: [email protected] > 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). >>
