Applications 
   When protecting telecommunication circuits, P devices are connected across Tip and Ring for metallic protection and across Tip and Ground and Ring and Ground for longitudinal protection. They typically are placed behind some type of current-limiting device. Common applications include:

• Central office line cards (SLICs)
• T-1/E-1, ISDN, and xDSL transmission equipment
• Customer Premises Equipment (CPE) such as phones, modems, and caller ID adjunct boxes
• PBXs, KSUs, and other switches
• Primary protection including main distribution frames, five-pin modules, building entrance equipment, and station protection modules
• Data lines and security systems
• CATV line amplifiers and power inserters
• Sprinkler systems