The 1669-06 is used for full weather protection of field transmitters and instrumentation operating on 12-28 V systems, the 1669 Series protects sensitive I/O circuitry from surges of any polarity or magnitude. Principal use is on 4-20 mA control loops and can be used on grounded (+ or -) or ungrounded circuits. Able to survive and protect even from direct lightning strikes to the transmitter ground or field wiring. Automatic recovery after passage of the surge. Long life, high operational reliability.