The MLP-270T protects the equipment when the voltage on the pair rises above 270V. It also opens the line when the current goes over 150ma. When the voltage or current goes back below the threshold, the MLP-270T automatically resets.
You should order a Ground Lug to attach the ground wire to the screw on the side, or you can order a Wall Mount Ground Bus & Lug to mount the MLP-270T to the wall with up to 6 Protectors (for 6 Lines).
If the line doesn't have ring voltage, use one of our lower voltage MLP Protectors. If you don't know the voltage on the line (and there is no ring voltage), put a DC volt meter across the pair to determine the voltage that's on the line normally, then choose a protector that has a higher voltage threshold than what you read (by at least a couple of volts).
Our MLP Protectors come in the following thresholds: 14V, 21V, 30V, 56V, 70V, 110V, 123V and 270V.
You'll need one Protector for each regular phone line or analog station port (pair) with ring voltage.
If you're putting this on an analog station port going to another building (OPX), be sure to put them at BOTH ENDS of the cable leaving the buildings!