configured for open transition automatic transfer initiated
and watt-hour meter with demand register. Meters shall
through the use of an under-voltage relaying scheme.
be pulse type for connection to the BAS. Switchgear shall
Breakers shall be of the electrically operated draw-out
be front and rear accessible. Aluminum bus will not be
type.
acceptable.
Network Substations. Generally speaking, network
All breakers in the 480 volt rated service main switchgear
substations are close-coupled to the secondary
shall be fully rated. Series rating will not be permitted for
switchboards servings the respective loads. All circuit
this equipment. Main and feeder breakers shall be
breakers up to and including the secondary switchgear
provided with integral solid-state ground-fault protection
main circuit breaker and accessories shall be of the
tripping elements.
draw-out type.
Main Switchgears (208 V service). 208 V service
Transformers. Substation transformers shall be dry-type
switchboards as well as substation secondary switchboards
with epoxy resin cast coils or liquid filled, 300 degree C
shall be freestanding and shall be provided with a single
insulation, non-petroleum based insulating oil type.
main service disconnect device. This main device shall
Liquid filled transformers shall be used outdoors and for
be insulated case, power air circuit breaker or bolted-
below grade vault construction. Substations shall be
pressure fusible switch (where appropriate), shall have
located at least 30 m (100 feet) from communications
ground fault protection, and shall be individually
frame equipment to avoid radio frequency interference.
mounted, draw-out type (as applicable). Insulated case
Provide lightning arrestors on the primary side of all
and power air circuit breakers shall be electrically
transformers. Provide surge suppression on the secondary
operated. Branch feeders shall be protected, either by
and/or downstream busses.
fusible load-break switches or fully rated molded case
Where silicon or oil filled transformers are used, the
circuit breakers. Front access only will be acceptable.
design must comply with all spillage containment and
Aluminum bus will not be acceptable.
electrical code requirements.
Surge Suppression. Provide surge suppression on the
main incoming service secondary switchboard.
Secondary Distribution
Main Switchgears (480 V service). In the case of double-
ended substations all main and secondary feeder breakers
are draw-out power type.
182 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
6.5 Distribution System Alternatives
Revised March 2005 PBS-P100
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