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).
