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).
