Accelaterm
®
Installation and Service Manual
30
CIRCUIT PROTECTION
OVERCURRENT PROTECTION
External Circuits
The Accelaterm provides 12VDC power to the badge readers,
accessory devices, and electric locks. Equipment requiring
5VDC may receive battery-backed power from the Ac-
celaterm. Self-resetting PTC devices are used to protect the
Accelaterm from excess loads and to minimize risk of fire
from external short-circuits. Remember a PTC will not self-
reset until the fault is discovered and removed. In some in-
stances, the circuit may need to be interrupted, conveniently
done by removing the connector to the affected circuit.
The limits given below are for
each
output circuit, independ-
ently protected by a PTC device. This limits the effect of a
single fault to the individual circuit.
Transient Protection
Nearby lightning discharges induce high-voltage transients
into the field wiring of electronic equipment. The Accelaterm
Access Control Panel provides protection from high-voltage
transients at all field wiring terminals. This includes all
Alarm Inputs, all Reader Connections, all 5V and 12V Acces-
sory power outputs, etc. The normal dielectric isolation of the
relay circuits is supplemented by MOV devices that are active
for both the dry and wet contact circuits. MOV snubbing de-
vices improve the life of the relay contacts.
Dielectric Isolation
The Ethernet Port meets the IEEE 802.3 Specification Stan-
dard for 1500V RMS Dielectric Isolation. Dielectric Isolation
is the appropriate technology because both ends of the cable
are connected to grounded equipment, and would be subject
to very high ground loop currents if the circuits were not iso-
lated.
Note that UL294 states that the connected communication
equipment (Ethernet Bridge, Host Computer, or Server) must
use signal-line transient protection equipment compliant to
UL497B, having a maximum marked rating of 50V.
Note:
Suitably qualified third-party equipment is available from
several vendors.
The Isolated 485 Interface option for the Accelaterm also in-
corporates transient protection, needed because of the long
signal wiring supported. But because the connection between
EIA/TIA-485 equipment is normally grounded, lightning dis-
charges to ground will cause damaging high ground loop cur-
rents if the equipment is not isolated. For this reason, the Ac-
celaterm 485 Interface adds high dielectric isolation to the
high voltage transient protection.
Type of Output
Current Limit
12 Reader Power Output
350mA (8 or 16 Circuits)
LED Output
(Sink to Ground)
100mA (8 or 16 Circuits)
5V Accessory Power
1.5A (2 or 4 Circuits)
12V Accessory Power
600mA Total for 2 Circuits.
Relay Contact Circuit
2.0A for Wet or Dry Contacts
Note:
These PTC current limits are more stringent than required
for [safe] power-limited output circuits.
Table 15 - LED Diagnostic Functions
