Install Off-premises Circuit Protection���

Protection from hazardous voltages and currents is required for all off-premises (out of building) trunks, lines, and terminal installations. Both over-voltage protection (lightning, power induction, and so forth) and sneak current protection are required. Sneak current protectors must be either UL listed/CSA certified, or must comply with local safety standards.

Sneak current protectors must have a maximum rating of 350 mA and a minimum voltage rating of 600 V, or as required by local regulations. The following devices protect the system from over-voltages:

• Analog trunks use the 507B sneak protector or equivalent. Over-voltage protection is normally provided by the local telephone company.
• Analog voice terminals use one of the following types of combined over-voltage and sneak current protection, or equivalent:
• Carbon block with heat coil for UL code 4B1C
• Gas tube with heat coil for UL code 4B1E-W
• Solid state with heat coil for UL code 4C1S
• DCP and ISDN-BRI terminals use the solid state 4C3S-75 with heat coil protector, or equivalent.
• DS1/T1 circuits require isolation from exposed facilities. This isolation may be provided by a channel service unit (CSU) (T1), or other equipment that provides equivalent protection.