Rice Lake SURVIVOR ATV - Manual (Page 13)

Connecting Electronic Equipment 9
3.3 Single-Point Ground Conductor
A bare 10 gauge solid wire is run from the scale frame to the main AC power earth ground. If DC transient
protection is included, it must be properly grounded to function correctly.
3.4 Electrical Ground Connections
Important
Improper grounding systems on outdoor truck scales often cause corrupted data from ground-loop
current flows and costly lightning damage to electronics.
Always strive for a single-point grounding system (see Figure 3-4). Do not drive ground rods at the scale location
to establish separate earth grounds for the scale. These separate earth grounds do not share the same zero reference
as the existing earth ground for the AC power system. This difference in electrical potential invites ground-loop
current flow between the separate grounds, often corrupting serial data like RS-232 which depends on a stable zero
reference.
In addition, a separate earth ground system at the scale can actually invite lightning or power surge damage:
• A minor power line surge in the scale house electrical supply should immediately be shunted to ground. If
a separate ground system exists at the scale with a lower potential than the main ground, the surge may
travel out to the scale ground rod, damaging load cells on its way.
• A nearby lightning ground strike may instantly raise the zero potential of a ground rod at the scale location,
while leaving the scale house ground rod unaffected. That lightning surge now takes the easiest path to the
lower-potential ground—through the scale wiring and back to the scale house ground, possibly damaging
the indicator on its way.
Therefore, the best grounding system for the scale is the same one used for the incoming AC power system. The
120 VAC power source used to power the indicator is connected to an existing earth-grounded rod system at the
scale house or other building where the indicator is located. This should consist of a double ground rod system of
two 5/8" x 8' copper rods driven 8' deep at the service entrance where the local utility company brings their lines
into the building.
The local utility company can test the resistance of the existing ground rods with a clamp-on megohmeter that
measures zero resistance. A reading of 3 3/4 or less is acceptable as a ground. If the test determines that the
grounding system is inadequate, the utility company can suggest methods to improve the system. It is crucial that
the scale owner authorize and make the recommended improvements to ensure an adequate electrical ground. Do
not connect the scale to the AC power supply until the grounding system is adequate.
Be certain each load cell grounding strap is securely connected to the top plate and bottom plate of each load cell
mount. Some models have ground straps included to install between modules. These inter-module straps ensure
that the entire scale is connected to the same single-point ground. There should be metal-to-metal contact with no
presence of paint or grout. This strap is designed to channel power surges on the deck around—rather than
through—the load cell to ground. A thick coating of anti-oxidant grease should be maintained on all ground
connections to prevent corrosion.
A separate grounding system conductor must extend uninterrupted from the main service panel ground to the scale
to protect load cells and scale wiring from lightning and other transient damage. This ground wire conductor must
be an unsheathed #10 copper wire or larger. Run the bare ground wire conductor intact from the AC power ground
rod to the scale in a separate trench. Bring the wire up from the trench near the J-box and attach it to the ground lug
located in the J-box pocket. This grounds the scale frame to the same single-point ground as the AC power for the
indicator.
A ground wire is included to attach the J-box ground lug to the ground lug located in the J-box pocket. Grounding
of the J-box is essential for operation of the DC transient protection incorporated into the J-box.