Glen Garside has the correct notion: it depends ... on the standard(s) used for the evaluation and the application within the equipment. The anticipated installation environment must certainly play a role in just how intensely reliable an earthing connection needs to be.
The general philosophy is to maintain a reliable earthing interconnection system. The reliability must be maintained during normal operation, service, maintenance or repair of the equipment. It can be thought similar to hanging a "do not disturb" sign on a hotel door. How this may be achieved is not normally prescribed in standards and one must apply common sense and ignore common cents (which is the normal driver for reducing the number of earthing studs). In my opinion, it is desirable for every earthing connection to have a separate termination, but this is not always practical or even necessary. There are instances where PE connections are reliably maintained, even when stacked. For instance, equipment using two detachable power supply cordsets, where the appliance inlets are in proximity to one another. Inlets are not normally removed for service, maintenance or repair functions, so there is little reason to despair at using a single stud. On the other hand, if the inlets are not proximate to one another, separate studs represent best practice, since PE connections should be brought to the chassis as close as practicable to where the supply conductors enter the equipment. Where the equipment is hard wired, as is the case for most NEBS environment equipment, a separate PE terminal for each supply is requisite. Where installation codes in the US and Canada apply, separate PE terminals are required. Other considerations would have to include equipment where such high secondary circuit currents flow that failure to maintain tight equipotential bonding within the equipment can cause significant interoperability issues. In such cases, though, studs may be a poor choice and ground bars and similar devices are better suited to the task. Regards, Peter L. Tarver, PE Product Safety Manager Sanmina-SCI Homologation Services San Jose, CA [email protected] This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
