AMCI SD17060E2, Руководство пользователя

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Networked Indexer/Driver User Manual
ADVANCED MICRO CONTROLS INC.
90
Grounding (continued)
Grounding Electrode Conductor
Connection of the ground bus to the Grounding Electrode System is
made with the Grounding Electrode Conductor. The Grounding
Electrode Conductor should be the shortest length of stranded wire
or braid possible. The American NEC allows a length of up to six
feet, but shorter is better. A shorter length will help shunt high fre-
quency noise to the Grounding Electrode System.
In extremely noisy environments, it is sometimes advisable to run
two wires from the ground bus to the GES. The length of these two
wires should differ by 20% to 30% so they offer different imped-
ances to the noise frequencies being shunted to earth ground.
The minimum sizes for the Grounding Electrode Conductor are #8
AWG stranded wire or 1" braid, but larger sizes may be needed
depending on the total ground fault current your system can gener-
ate. The actual size is determined by the size of the largest conductor
in the system.
The American NEC allows the use of a solid wire for the Grounding Electrode Conductor but this should be
avoided. High frequency currents (electrical noise) travel along the surface of a conductor. Heavy gauge
stranded wire and braid both have large surface areas, solid conductors do not. Therefore, stranded wire and
braid have a much lower effective resistance to electrical noise.
Grounding Wires
Grounding wires are used to connect the pieces of equipment to your ground bus. AMCI strongly suggests
using #8 AWG stranded wire or 1" wire braid for all grounding connections. The American NEC allows the
use of solid wire for grounding wires but this should be avoided for the same reasons they should not be used
for the Grounding Electrode Conductor.
Avoiding Grounding Problems
As stated before, there are two reasons to properly ground a system. The first reason is to protect human life.
A properly designed grounding system will be able to detect potential shock currents and remove power from
the system. The second reason is to improve system reliability by shunting electrical noise currents to earth
instead of allowing them to flow through the system where they can disrupt the operation of electronic con-
trols.
The entire grounding system, even though conductive, is not meant to carry current except under fault condi-
tions.
Under normal operating conditions, the grounding system should not carry any current
at all.
Ground Fault Interrupt (GFI) circuits depend on this condition to work correctly. Any ground current flowing
through a GFI is considered a fault condition and the GFI immediately opens to remove power from the
faulted circuit.
By this definition, electrical noise and other transient currents such as inductive spikes are considered fault
currents. The fact that these currents are very short lived and of relatively small power allows them to be
safely shunted without tripping a Ground Fault Interrupt circuit.
Figure R8.1 Grounding Components