TB9100/P25 CG/P25 TAG Installation and Operation Manual Installation 77
© Tait Limited March 2014
Where the E&M output circuit is used to switch power to an inductive
device, such as a relay, that device must have efficient suppression to absorb
the inductive spike that occurs when the current is switched off. If the peak
spike voltage exceeds
± 58V the circuit protection devices might trigger and
latch on. Where the relay is powered from 48V or more, only a silicon diode
in parallel with the relay coil will provide a sufficiently tight clamping
voltage. For lower switched voltages a Zener diode or MOV may be used
provided its worst case clamping voltage does not exceed 58 V. RC transient
suppression circuits should be used with caution: these require careful design
to meet the suppression objectives.
4-Wire Audio Line Interface
If DC is applied to the 4-wire audio lines, the nominal voltage should not
exceed 48V. Under no circumstances should the peak voltage exceed 58V
otherwise the protection devices may be triggered.
As for the E&M leads, any DC applied to the 4-wire lines should be current
limited to no more than 120 mA, so as to allow the protection devices to
unlatch after a transient event.
The on-board protection devices are to be regarded as ‘secondary
protection’ only. Generally they are only suitable for relatively benign
environments such as internal building wiring or short run underground
wiring. If more severe conditions are expected it is advisable to fit external
primary protection devices.
Where there is a possibility of ‘power-cross’ conditions occurring, externally
fitted fuses or PTC resistors are required to prevent any long-duration high
currents burning out components on the audio line interface. Such current-
limiting protection is mandatory for telco administrations requiring
compliance to BellCore standard GR1089 or the power cross tests of
UL60950 or ITU K.21.
External Fuses or PTC resistors are also required if the equipment is required
to be compliant with the current-limiting conditions specified for
protecting external telco and customer premise wiring as per GR1089 and
UL60950.
Tait have used the Krone Comprotect 2/1-CP BOD190A1 product, part
number 5909 1 078-40.
Connecting General Purpose Inputs and Outputs
The base station has a number of configurable general purpose inputs and
outputs. These are connected via the 9-way D-range. Pin 1 and Pin 9 can
have different functions: select the function you want using the CSS. Digital
inputs and outputs require Task Manager programming before they are
operational. Refer to the CSS Help or manual for further information.
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