Grounding Conditions; Grounding - NEC Express5800 1080Xd User Manual

Grounding Conditions

Grounding

The site building shall provide a safety ground/protective earth for each AC service entrance to
all system cabinets. Install a PE (protective earthing) conductor that is identical in size,
insulation material, and thickness to the branch-circuit supply conductors. The PE conductor
must be green with yellow stripes. The earthing conductor described is to be connected from the
unit to the building installation earth or, if supplied by a separately derived system, at the supply
transformer or motor-generator set grounding point.
As the grounding for computers, have a designated grounding line up to the computer's power
distribution panel. The grounding resistance in this case should not be more than 100Ω. For
information on its thickness, refer to(2) Grounding condition (a). The grounding for computers
shall be basically independent from other devices.
(1) Purpose of grounding
Computer devices are grounded for the following purposes.
(a) Reduced grounding voltage
To aim for reduced contact voltage by connecting the ground with a low resistance
when high voltage is applied to the frame due to an insulation breakdown of a device
or a cable, etc.
(b) Prevention of inductive failures, etc.
To place the voltage potential between the computer device frame and the ground on
the same voltage potential level as that of the ground by allowing the voltage potential
generated through electrostatic induction to the ground.
(c) Reliable operation of the circuit breaker
Actively pass the ground current to the ground to secure a reliable operation of the
leakage breaker in case of accidents of defective insulation.
(d) Prevention of power supply failures
To aim for reduction of power supply failures by actively operating the over-current
breaker when in error.
(e) Realization of equal voltage potential to the ground
To aim for prevention of electric-shock disasters by equalizing the voltage potential to
the ground based on a single-point grounding method.
(f) Prevention of contacts between low and high voltage circuits
To aim for prevention of insulation breakdown of low voltage circuits and electric-
shock disasters deriving from contacts between low and high voltage circuits.
(2) Grounding conditions
When performing the grounding work, make sure to pay attention to the specifications
defined by NEC in addition to the definitions of electric facility technology standards.
(a) The thickness of the grounding conductor should be at least 8 mm
cross section and the same or larger than the main power cable. In the case of the
medium- or large-size system, this should be at least 38 mm
(b) Two cables are required for the grounding: one dedicated for computer grounding and
the other for security type-D grounding.
Express5800/1080Xd/1160Xd/1320Xd Site Preparation Guide 13
2
in terms of the
2
.