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ENGINEERING DATA SHEET 1A32007
EXCEL
SEISMIC GUIDELINES FOR USERS OF SHEET 1 OF 1
PRLC / PRLI LOW VOLTAGE SWITCHBOARDS
2/12/07
1. A generic type NEMA 1 and NEMA 3R PRLC/PRLI low voltage switchboard assembly was attached to a
triaxial seismic simulator to duplicate the effects of an earthquake.
2. When type PRLC/PRLI switchboard is subjected to an earthquake, stress is applied to the foundation. The
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, proper
mounting is the single most important factor in withstanding a seismic occurrence. The foundation must be
designed to withstand the reaction loads imposed on it by the equipment. Foundation embedments shall be
designed to transfer the ultimate capacity of the anchor bolts. The ultimate capacity is to be calculated by the
architect or consulting engineer.
3. When a PRLC/PRLI switchboard is subjected to an earthquake, it moves. The amount of motion depends on the
magnitude of the earthquake. The top of the cabinets experience the greatest degree of motion. The maximum
top-of-cabinet response motions measured during the seismic tests are listed below. The user should
reference these to decide what (if any) special flexibility may be needed at interfaces.
TOP OF CABINET
MAGNITUDE OF ACCELERATION
RESPONSE MOTION
1.2 G's 4.0 IN. FRT. TO BACK
3.25 IN. SIDE TO SIDE
2.75 IN. VERT.
Conduit layout in concrete for loads entering and/or exiting the bottom must be designed and installed to prevent
damage from an earthquake. If top entry is necessary, seismic fittings or flexible conduit is needed.
4. When a switchboard assembly is separated into groups of vertical sections for shipment, the user must be sure
to install the inter-unit tie bolts. Failure to join sections together could result in damage to the equipment during
an earthquake.
5. Incoming power cables should be lashed together, and they should be secured to the structure at least every
four feet.
6. Any drawout type circuit breaker and/or fuse truck should always remain in the connected position, or they
should be secured somewhere remote from the switchboard.
7. The user should provide storage areas to secure mobile pieces of equipment (such as spare breakers or
drawout ratchets) away from hinged panels on which relays and other instruments are mounted so they are not
damaged during an earthquake.
8. WARNING - Certain types of protective relays have rather delicate operating mechanisms. Especially when
set to operate quickly or at low pick-up levels, these relays may cause subsequent spurious circuit breaker
operations during the earthquake.
9. Center of Gravity - For seismic calculations, the following dimensions should be used to locate the center of
gravity for type PRLC and PRLI low voltage switchboards. These dimensions are applicable for all switchboard
lineups.
Vertical: 60 inches from base of switchboard
From left to right: Geometric center of the switchboard
From Front: Two fifths the depth of the switchboard
Weights may be found on the equipment drawings provided for the specific project.