Standards for Sizing Equipment and Systems
Visual Impact. Options regarding the location and
selection of electrical work that will have a visual impact
To ensure maximum flexibility for future systems changes,
on the interior and exterior of the building shall be closely
the electrical system must be sized for the demand load
coordinated with the architectural design. This includes
with additional spare capacity as follows:
placement and specification of lightning protection
system, colors and finishes of lights, outlets, switches, and
Panelboards for branch circuits: 50% spare ampacity
device plates.
as well as 25% spare circuit capacity.
Panelboards serving lighting only: 25% spare ampacity
Equipment Grounding Conductor. Except for isolated
as well as 25% spare circuit capacity.
ground systems, all low voltage power distribution
Switchboards and distribution panels: 35% spare
systems shall be supplemented with a separate, insulated
ampacity and 25% spare circuit capacity.
equipment grounding conductor.
Main switchgear: 25% spare ampacity and 25% spare
circuit capacity.
provided in accordance with NFPA 780. The system shall
Spare overcurrent devices shall be provided as well as bus
be carefully designed to ensure that static discharges are
extension for installation of future protective devices.
provided with an adequate path to ground. Surge
arrestors on the main electrical service shall also be
Prior to adding the spare equipment ampacity to account
considered.
for future load growth, it is important that the load study
reflect actual demand loads rather than connected loads.
Artwork. Museum standards for lighting works of art
The designer shall apply realistic demand factors by taking
range from 5 to 10 foot-candles for extremely light
into account various energy conserving devices such as
sensitive materials such as paper and textiles, to 20 to 40
variable frequency drives applied to brake horsepowers,
foot-candles for moderately sensitive materials such as oil
energy efficient motors, occupancy sensors, etc. The
paintings and wood.
designer shall also avoid adding the load of stand-by
motors and shall be careful to distinguish between
Please consult Chapter 4.1, Installation Standards, of the
summer and winter loads by identifying such "non-
Fine Arts Program Desk Guide for additional information.
coincidental" loads. A "diversity factor" shall be applied
to account for the fact that the maximum load on the
elevator system, as a typical example, does not occur at
the same time as the peak air conditioning load. Once
the estimated "peak demand" load is established then the
factor for load growth shall be added.
176 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
6.3 Design Criteria
Revised March 2005 PBS-P100
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