Mains Earth Ground Stack

[metrologist]

Are we all aware that the earthing ground wire should be attached directly to the chassis first, and any additional internal ground wires must then be fastened with a separate fastener? For example, a single screw/stud and a single nut should not be used to attach both mains ground and another ground wire that may run to other assemblies, such as PCB or front panel? Should this be common engineering knowledge?

[james_s]

What's wrong with using a single screw star ground arrangement? I certainly see it done that way in a lot of gear.

[metrologist]

There is an IEC standard, but there seems to be a qualified risk of that one point coming loose and undoing the main earth ground, when other connectors are involved.

Another question, also defined is lack of mains supply gap from other circuits. Is there an insulative card that can be inserted between a supply PCB and chassis or other PCB? The "sandwich" will not pass. We need about 0.5mm more gap and there is no room without significant impact.

[ciccio]

In a  project that required CE compliance testing and approval from a certified lab, I needed to use the same screw (actually a threaded insert) for both the PE connection and another ground wire.
It was acceped but with the following mandatory requirements:
The PE wire's ground lug must be the first, with a serrated washer under it (against the case's metal, to guarantee contact even if the case is oxidized), an elastic washer over it (to maintain contact pressure and avoid loosening due to vibration), than a nut that must be serrated with a specified torque.
The other wire's lug can sit the top of this nut, and can be locked with another elastic washer and a second nut.

And do not forget thar the PE connection must be labeled with the relevant Earth symbol, so any service technician will know that this connection must not be tampered with

[ciccio]

Another question, also defined is lack of mains supply gap from other circuits. Is there an insulative card that can be inserted between a supply PCB and chassis or other PCB? The "sandwich" will not pass. We need about 0.5mm more gap and there is no room without significant impact.

I use DuPont's NOMEX paper. There are different suppliers. Even RS has it.

Best regards

[metrologist]

Thanks. This is to comply with IEC 61010-1. We'll ask the test house about the nomex paper for our application.