Applications
 RS-422/RS-485 communications
 RTD applications
 Industrial and building automation
 AISG control lines
 T1/E1/J1 lines (see note below)

Features
 Protection for up to four pairs of lines
 Three-Stage protection
 Superior to diode or TVS only based designs
 Weatherproof ABS enclosure
 Removable screw terminal blocks

Description
The AL-D4-05W is a high performance 3-stage weatherproof protector that provides superior protection of
differential or balanced digital or analog lines from transients and surges. This unit will protect up to four pairs of
lines or eight single ended data, analog or control lines.
The first stage is comprised of a differential gas discharge tube. Stage two is a pair of current limiting series
resistors and the final stage is a low capacitance diode array. The use of three terminal differential gas discharge
tubes provides superior common and differential mode protection against conducted transients versus the use of
lower cost two terminal tubes. The second stage series resistance limits the power dissipation of the fast diode
clamp array in the third stage. This allows time for the slower but higher power gas tubes to flash over. The diode
array clamps the leading edge of fast transients to safe levels until the high power gas tubes turn on. This
eliminates the damaging leading edge spike that single stage gas tube
protectors let leak through. The diode array’s low capacitance assures that the
suppressor will not degrade the high-speed signals. The 3-stage design can
handle higher-level transients than a protector that uses only diodes.
Failsafe Feature
The AL-D4-05W series is designed to convert into a failsafe mode in the rare
case of a catastrophic surge or lightning event. For this mode, the resistors in
the second stage will fuse and portions of the diode array will short. This
effectively disconnects the line from sensitive equipment thus limiting damage.
The units are factory repairable.