Fred:
The IEC 801-2 standard specifically details how the EUT is to be
placed for testing. The ground coupling planes are connected to earth
ground differently for the 1984 and 1991 versions of IEC 801-2. The
1984 standard includes only a horizontal coupling plane connected
directly to earth ground. The 1991 version adds a vertical coupling
plane, and both are connected to earth ground through two in line
resistors of 470 kOhms by separate wires. In either case, the test
setup calls out distances between the EUT and the coupling planes and
should remain consistent from test house to test house for the same
version of the standard.
If I understand your situation correctly, the connection to ground
that you are referring to is how your equipment (the EUT) is grounded.
I believe that the standard states that the EUT shall be configured
per the manufacturer's instructions/specifications. Therefore, if you
specify that the EUT may be connected to no earth ground, an external
ground stud, or some other way, it should comply with each possible
configuration (or the worst possible configuration).
In my experience, I have seen equipment fail the ESD test when the
ground was being supplied through an I/O cable from support equipment
and pass once this cable was removed. As you stated, the ESD will
look for the shortest path to ground. Therefore, grounding the metal
case of the EUT directly to earth ground (AC ground or ground stud) in
most cases will be better than a ground path that will travel through
some of your circuitry. However, it is also possible to have a
non-conductive enclosure that may not accept the discharge.
Just my two cents worth. Good luck.
Ken Shadoff
The above opinions are my own.
______________________________ Reply Separator _________________________________
Subject: IEC801-2
Author: Fred Waechter <[email protected]> at ~internet
List-Post: [email protected]
Date: 12/9/96 12:06 PM
This is in relation to testing a Class II, 2 wire system to the European
IEC801-2 electrostatic discharge requirements.
The system is used in an environment that may have no earth ground, or
earth may be tied back at the substation, or earth may be tied at
multiple points along the AC neutral, or an earth ground rod me be
available at the users end installation.
On application of an ESD pulse to this system, the energy in the ESD
pulse will try to find the shortest path to earth ground.
1. Is there a preferred test method to insure conformity of testing
between test laboratories, and also the users end installation as their
methods of earthing may certainly differ?
2. Would different methods of earthing result in differing results due
to differing amounts of system discharge before the next ESD pulse is
applied to the system?
These questions were prompted by results obtained at two different test
laboratories.
The systems passed when tested at an independent test lab. in Taiwan.
The same units failed when tested by a lab. in the U.S.
Thanks for your help.
