MDF connections to stations and the public switched telephone network
54 Installing and Connecting the MDF and Telephones
Protection from hazardous voltages and currents is required for all off-premises (out of building)
trunks, lines, and terminal installations. Protection for incoming analog trunks is required
between the incoming RJ21X or RJ2GX network interface and the media gateway for both trunk
and off-premise circuit packs. Both over-voltage protection (lightning, power induction, and so
forth), and sneak current protection are required.
Note:
Note: Sneak current protectors with a rating of 350 mA at 600 volts must be
Underwriter’s Laboratory, Inc. (UL) listed for United States installation and
Canadian Standards Association (CSA) certified for Canadian installation.
The following devices protect the media gateway from over-voltages:
●Analog trunks use the 507B sneak protector or equivalent. Over-voltage protection is
normally provided by the local telephone company.
●DS1/E1/T1 circuits require isolation from exposed facilities. This isolation may be provided
by a CSU (T1), LIU (E1), or other equipment that provides equivalent protection
●Analog telephones use 146 Series Line Protectors combined over-voltage and sneak
current protection, or equivalent: See PEC 8310-0xx; SAP Code 10512x.
●DCP and ISDN-BRI terminals, and E&M tie trunks, use a low voltage version of the 146
Series Line Protectors.
The Model 507B sneak current fuse panel, or equivalent, is recommended for sneak current
protection for analog trunks. The panel contains two 25-pair connectors, one fuse removal tool,
and 50, 220029 sneak fuses (and two spares). Each column of sneak fuse panels requires
approximately 8 inches (20 centimeters) of horizontal wall space.
See Figure 26: Model 507B sneak fuse panelon page 55. See Table5: Sneak fuse panel
ordering information on page 55 for ordering information.