This Outline of Investigation covers supplementary requirements for communication circuit packs and
shelves with remote feeding telecommunication circuits intended for backwards compatibility with
frames, shelves and backplanes.
The equipment covered is limited to that which forms part of a telecommunication network up to and
including the demarcation point. The circuitry associated with this type of equipment is intended to
be installed and located in service access areas only, which may or may not be provided by the
equipment housing. This equipment is generally considered Central Office Equipment, though it may be
deployed elsewhere in similarly controlled environments.
This Outline supplements UL 60950, Third edition, because of the need for backwards compatibility of
new equipment with equipment already installed in the existing telecommunications infrastructure. In
particular, spacings associated with connectors and similar interfaces that are part of the installed base
are incompatible with UL 60950 based on the existing working voltages. Certain types of equipment
have provided voltage biased circuitry for many years which are directed within the telecommunication
network. These high-voltages are utilized to power signal repeaters and remote terminal equipment
where AC power cannot be relied upon for operation due to the tremendous downtime present with AC
utility functionality. The circuits are not used in customer accessible areas where accidental contact
would present a potential hazard. Network service personnel are considered to be aware of the
apparent hazards associated with this type of circuitry.
Examples of equipment requiring backwards compatibility are:
~ Circuit packs or cards with existing or new technologies designed to be installed into shelf
assemblies that form part of a service provider's existing infrastructure;
~ Shelf assemblies intended as replacements for existing shelf assemblies mounted in frame
line-ups that form part of a service provider's existing infrastructure; and
~ Shelf assemblies or enclosures intended as replacements for existing service provider
infrastructure equipment that are required to be compatible with cards or circuit packs already in
service.