As I see it, the star between the lug and the sheet metal is for for conductivity.  The star above the lug is for mechanical securement.  It is therefore possible to use additional techniques for mechanically securing the fastener; SEM screws, KEP nuts, jam nuts, etc. If you think about the path current takes you realize the metal parts located above do not actually contribute to conductivity.  

A German safety engineer I know from LGA Nuremberg used to press his thumb sideways against the lug and try to loosen the connection. A proper hardware stack up would always prevent this. 

Have a great weekend, Doug


Sent from my Android on the Verizon 4G LTE Network

From: scott...@gmail.com
Sent: August 11, 2018 3:13 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Reply-to: scott...@gmail.com
Subject: Re: [PSES] External toothed star washer used in earth connection

Scott,

Thanks for your sharing experience on this matter!  What is the purpose for the second star washer?  Double protection on top of the first one.  The star washer is a very essential part for the success of good earth the metal enclosure.

Regards,

Scott


On Sat, 11 Aug 2018 at 02:11, Scott Douglas <sdouglas...@gmail.com> wrote:
Many years ago a TUV Engineer drummed into my head "the only acceptable way" to make protective earth bonds was chassis > star > ring lug > star > nut for ground studs pressed into the chassis.


On Fri, Aug 10, 2018, 9:54 AM Scott Xe <scott...@gmail.com> wrote:

Hi Rich,

 

Thanks for your advice! 😊  Regarding the flat washer, can it be the flat ring lug of the connecting wire instead?

 

Between the screw head and the metal enclosure, do we need a flat washer?  That is to say: screw head -> flat washer -> metal enclosure -> on other side of metal enclosure with paint removed in the contact area with the flat ring lug -> flat ring lug of the earthing wire -> split ring lock washer -> plain nut to establish a good electrical earth connection.

 

Thanks and regards,

 

Scott

 

Sent from Mail for Windows 10

 

From: Richard Nute
Sent: Friday, 10 August 2018 03:11 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] External toothed star washer used in earth connection

 

 

"The lock washer should not interface between the bolt head and the metal, the lock washer should be between the head and a flat washer."

 

That locks the bolt to the flat washer so they turn together.  😊

 

Establishes a good electrical connection between the bolt and the flat washer!  😊

 

Rich

 

 

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