Provide isolation transformers, electronic power
High Frequency Power System Grounding. If requested
distribution panelboards or power conditioners to serve
by the User Agency, in addition to the low frequency
critical electronics equipment loads.
power system grounding, a high frequency signal
reference grounding system for radio frequency noise is
Provide isolated grounding service on dedicated circuits
required (with the two systems bonded together at one
to critical data terminating or communicating equipment.
point). A grid made up of 600 mm (2-foot) squares will
Replace metallic data and signal conductors with fiber
provide an effective signal reference grounding system.
optic cables where practical.
The raised floor grid may be used if it has mechanically
bolted stringers. Alternatively, a grid can be constructed
Harmonic Generation, K-Rated Transformers,
by laying a 600 mm mesh (2-foot squares) of braided
Sizing of Neutrals
copper strap or 1.3 mm (16 gauge, 0.051 inch) by 50 mm
(2-inch) copper strap directly on the structural floor
Harmonic frequencies are introduced into the branch
below the raised access floor. Data processing equipment
circuit distribution system by the power supplies of the
shall be connected to the reference grid by the most direct
following items of equipment:
route with a braided copper strap.
Electronic ballasts
Variable frequency drives
Common Mode Noise Reduction. The reduction of
common mode noise is particularly important for the
PC's
proper operation of computer-based, distributed
Laser printers
microprocessor-based systems, i.e., building automation
File servers
systems, electronic security systems, card access control
Fax machines
systems, and local area networks.
Copiers
The following guidelines shall be considered to reduce
common mode noise:
The third order harmonics (180 Hz) add in the neutral
conductor and, in the case of 100 percent total harmonic
Avoid running unshielded metallic signal or data lines
distortion, would result in a neutral current of 1.73 times
parallel to power feeders.
the phase current.
Where metallic signal or data lines must be routed in
noise prone environments, use shielded cables or install
K-Rated Transformers: (K-13) with a 200 percent neutral
wiring in ferrous metal conduit or enclosed cable trays.
shall feed branch circuit panelboards with 200 percent
neutrals.
Locate metallic signal or data lines and equipment at a
safe distance from arc producing equipment such as line
voltage regulators, transformers, battery chargers, motors,
generators, and switching devices.
205
ELECTRICAL
ENGINEERING
6.13
Clean Power Systems
Revised March 2005 PBS-P100
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