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4-2 Electrical Installation
Grounding
Note: Displays MUST be grounded according to the provisions outlined in Article
250 of the National Electrical Code and according to the specifications in this
manual. Daktronics recommends a resistance-to-ground of 10 ohms or less.
The electrical contractor performing the electrical installation can verify ground
resistance. Daktronics Sales and Service personnel can also provide this service.
The display system
must
be connected to an earth electrode installed at the display.
Proper grounding is necessary for reliable equipment operation. It also protects the
equipment from damaging electrical disturbances and lightning.
Note: The display must be properly grounded, or the warranty will be void.
Refer to the schematics listed at the beginning of this section for information about
ground wire connection. The connection is illustrated in the “Pwr In” detail on each
of the schematics.
The material for an earth-ground electrode differs from region to region and may
vary according to conditions present at the site. Consult the National Electrical Code
and any local electrical codes that may apply. The support structure of the display
cannot be used as an earth-ground electrode. The support is generally embedded in
concrete, and if it is in earth, the steel is usually primed or it corrodes, making it a
poor ground in either case.
Power Installation
There are two considerations for power installation: installation with ground and
neutral conductors provided, and installation with only a neutral conductor provided.
These two power installations differ slightly, as described in the following
paragraphs:
Installation with Ground and Neutral Conductors Provided
For this type of installation, the power circuit
must
contain an isolated earth-ground
conductor. In this circumstance,
do not
connect neutral to ground at the disconnect
or at the display.
Note: This would violate electrical codes and void the warranty.
Use a disconnect so that all hot lines and neutral can be disconnected. The National
Electrical Code requires the use of a lockable power disconnect within sight of or at
the display.
Installation with Only a Neutral Conductor Provided
Installations where no grounding conductor is provided must comply with Article
250-32 of the National Electrical Code. If the installation in question meets all of the
requirements of Article 250-32, the following guidelines must be observed:
ƒ
Connect the grounding electrode cable at the local disconnect, never at the
display driver/power enclosure.
ƒ
Use a disconnect that opens all of the ungrounded phase conductors.