scheider electric MiCOM P746, Technical Manual

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P746/EN IN/G31 Installation
(IN) 15-4 MiCOM P746
IN
2. HANDLING OF ELECTRONIC EQUIPMENT
A person’s normal movements can easily generate electrostatic potentials of several
thousand volts. Discharge of these voltages into semiconductor devices when handling
electronic circuits can cause serious damage which, although not always immediately
apparent, will reduce the reliability of the circuit. This is particularly important to consider
where the circuits use complementary metal oxide semiconductors (CMOS), as is the case
with these relays.
The relay’s electronic circuits are protected from electrostatic discharge when housed in the
case. Do not expose them to risk by removing the front panel or printed circuit boards
unnecessarily.
Each printed circuit board incorporates the highest practicable protection for its
semiconductor devices. However, if it becomes necessary to remove a printed circuit board,
the following precautions should be taken to preserve the high reliability and long life for
which the relay has been designed and manufactured.
1. Before removing a printed circuit board, ensure that you are at the same electrostatic
potential as the equipment by touching the case.
2. Handle analogue input modules by the front panel, frame or edges of the circuit
boards. Printed circuit boards should only be handled by their edges.
Avoid touching the electronic components, printed circuit tracks or connectors.
3. Do not pass the module to another person without first ensuring you are both at the
same electrostatic potential. Shaking hands achieves equipotential.
4. Place the module on an anti-static surface, or on a conducting surface which is at the
same potential as yourself.
5. If it is necessary to store or transport printed circuit boards removed from the case,
place them individually in electrically conducting anti-static bags.
In the unlikely event that you are making measurements on the internal electronic circuitry of
a relay in service, it is preferable that you are earthed to the case with a conductive wrist
strap. Wrist straps should have a resistance to ground between 500k
Ω
to 10M
Ω
. If a wrist
strap is not available you should maintain regular contact with the case to prevent a build-up
of electrostatic potential. Instrumentation which may be used for making measurements
should also be earthed to the case whenever possible.
More information on safe working procedures for all electronic equipment can be found in BS
EN 100015: Part 1:1992. It is strongly recommended that detailed investigations on
electronic circuitry or modification work should be carried out in a special handling area such
as described in the aforementioned British Standard document.