Technical information

27
Installation
Noise Suppression
Electrical Noise
You can greatly reduce the effects of electrical noise on electronic equipment when you
follow the techniques outlined below.
If mixing wires cannot be avoided, then the low voltage control input and output wiring must
be shielded. The shield for these wires should only be connected to ground at the source end
of the cable.
1. Do not run low power control signals and high power wiring in the same raceway.
2. Do not connect both ends of a shielded cable to ground. You may create a ground loop
condition which could be very difficult to locate.
3. Keep all wires in the system as short as possible with consideration for troubleshooting
and repair.
4. Follow the recommended grounding arrangements.
5. Use suppression devices on relays and coils as outlined in the following section.
6. If control signal and high power wiring must cross, make sure they cross at a 90° angle.
Magnetic Coil Noise
To suppress transient noise in DC relay coils, install a diode across the coil in a direction that
will cause the voltage transient to be dissipated through the diode.
Figure 18: DC Relay Coil
For noise suppression in AC relay coils, install a capacitor-resistor network across the coil to
suppress the unwanted transient.
Figure 19: AC Relay Coil
The specific values of suppresser resistance and capacitance required may vary depending on
the inductance of the coil. Consult the relay manufacturer for the proper values to use. These
COIL
DC LINE
+
-
IN4004
OR
GREATER
COIL
AC LINE
47 OHM
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