Contrec 515, Operation Manual

Page: 26 / 92

Installation
18 515 HC04 - 8 June 2007
Figure 12 Relay Connection Diagram
RC Network for Interference Suppression
When driving highly inductive loads with the relay outputs, it is
recommended to use RC suppression networks (often called “Snubbers”)
for the following reasons:
•
To limit the amount of electrical noise caused by arcing across the
contacts, which may, in extreme cases, cause the microprocessor to act
erratically.
•
To protect the relay contacts against premature wear through pitting.
RC suppression networks consist of a capacitor and series resistor and are
commonly available in the electrical industry. The values of R and C are
dependent entirely on the load. However, if the user is unsure of the type of
snubber to use, values of 0.25
µ
F and 100
Ω
will usually suffice. Note that
only mains-approved RC suppression networks should be used.
The basic principle of the operation is that the capacitor prevents a series of
sparks arcing across the contact as the contact breaks. The series resistor
limits the current through the contact when the contact first makes.
Supply
Alarm
Relay 1
Relay 2
Relay 3
Relay 4
Alarm
Alarm
Alarm
R2
R1
R3
R4
RC
Relay Common
MOV
MOV
MOV
MOV
500