Tadiran Telecom Coral IPx 500, Installation Manual, Page: 516 / 544

9-88
Coral IPx 500 Installation Manual
R
elay Contacts
RL
Y
1
, RL
Y2, RL
Y3
9
If the contact is to operate a relay or solenoid, use an alternating current (AC) operated
device and an AC power source, if at all possible. AC operated inductive loads
produce much lower arc levels than direct current (DC) operated loads.
If the contact must operate a DC powered inductive load, the contact must be
adequately protected by arc suppression devices.
Figure 9-25
illustrates the use of a
common rectifier diode as a simple arc suppression device. The diode is normally
reverse biased (not conducting) with the cathode (top side in the drawing) connected
to the positive side of the power source.
Figure 9-25 DC Arc
Suppression for MSBipx
Relays
When the inductive load is powered, a magnetic field is created around the coil
windings. When power is removed, the magnetic field quickly deteriorates, producing
a reverse polarity voltage (counter EMF) across the windings. This reverse polarity
voltage is typically many times the voltage which originally powered the coil,
providing enough potential to arc across the open relay contacts.
By placing the diode in the circuit, the reverse polarity current is conducted by the
diode, shunting the energy around the contacts. A rectifier rated at 1.0 ampere forward
current (1.0A I
F
) and a peak inverse (reverse) voltage of at least 250 volts (250V, PIV,
PRV, or V
RM
) should be sufficient in most cases.
MSBipx
Coral
IPx 500
x
x
RLYx
RLYx
D.C.
Power
Supply
Relay
Spike
Suppression
Diode
(+) (-)
3
Auxiliary
Connector
RLY
2
12
37
13
38
14
39
1