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).
