1.8.2 Design Guidelines.
Design the shielding to conform to the needs of the system. Consider the relative ease of shielding
an individual equipment rather than shielding a room or the entire structure.
Assure that the shielding provided is sufficient to meet system needs (both known and predicted) but
do not excessively over design.
Use the inherent shielding properties of the structure to maximum advantage. Employ the small
amount of shielding (typically 10-20 dB) offered by reinforced concrete. However, do not expect common
building materials such as brick, concrete, wood, fiberglass, or plastic to provide any significant shielding to
electromagnetic signals (1-16).
Locate most sensitive and most critical equipments as close to the core of the structure as
operational requirements will permit.
To minimize the attenuation requirements on shields, predetermine the location of likely sources of
interference such as power substations, engine-generators, and RF transmitters; maximize the separation
between such sources and potentially susceptible equipments or systems.
Where a choice exists as to exterior skin materials for the shelter or structure (e.g., fiberglass
versus sheet steel or aluminum) choose metals to take advantage of their improved shielding properties. (In
order to utilize metal sidings as effective shields, seams must be electrically continuous.)
Insure that shield continuity is maintained at points of entry of signal cables, power conductors,
utility lines, and ground conductors.
Make sure that windows, doors, and ventilation ports are shielded along with the walls. Use well
bonded screen wire for windows, use metal doors, and apply honeycomb ducts or appropriate screening over
Equip all power lines supplying shielded areas with power line filters.
Use steel conduit in preference to aluminum conduit to take advantage of the improved magnetic
shielding properties of steel.
Use enclosed metal wiring ducts or raceways in preference to open mesh or unenclosed types.
If the only purpose of the shield is to establish a personnel barrier to prevent inadvertent contact
with dc and power frequency hazardous voltages, consider the use of nonconductive shields which may be less
expensive. (If metal shields are used to provide shock protection, they must be well grounded to the power
safety ground - the green wire network.)