Qualifications and Requirements
XPR300 Instruction Manual 809480 67
Recommended grounding and shielding
Introduction
This section describes practices for grounding and shielding a plasma cutting system to minimize its
susceptibility to electromagnetic interference (EMI) (also known as noise). It also describes the
service ground, protective earth (PE) ground, and DC power ground. The diagram at the end of this
section shows these types of grounds in a plasma cutting system.
The grounding practices in this section have been used on many
installations with excellent results, and Hypertherm recommends that
these practices be a routine part of the installation process. The actual
methods used to implement these practices may vary from system to
system, but should remain as consistent as possible. However, due to the
variation in equipment and installations, these grounding practices may
not succeed in every case to eliminate EMI problems. Hypertherm
recommends that you consult your local and national electrical codes to
make sure that the grounding and shielding practices that you use satisfy
the requirements for your location.
Types of grounding
Service ground (also known as safety ground) is the grounding system that applies to the incoming
line voltage. It prevents a shock hazard to any personnel from any of the equipment or the cutting
table. It includes the service ground coming into the plasma system and other systems, such as the
CNC and the motor drives, as well as the supplemental ground rod connected to the cutting table.
In the plasma circuits, the ground is carried from the plasma system chassis to the chassis of each
separate console through the interconnecting cables.
Protective earth (PE) ground is the grounding system inside the electrical equipment. The PE
ground, which connects to the service ground, provides electrical continuity between the equipment
and the AC service.
DC power ground (also known as cutting current ground or work) is the grounding system that
completes the path of the cutting current from the torch back to the plasma system. It requires that
the positive lead from the plasma system be firmly connected to the cutting table ground bus with a
properly sized cable. It also requires that the slats, on which the workpiece rests, make firm contact
with the table and the workpiece.
EMI grounding and shielding is the grounding system that limits the amount of EMI emitted by the
plasma and motor drive systems. It also limits the amount of EMI that is received by the CNC and
other control and measurement circuits. The grounding practices described in this section mainly
target EMI grounding and shielding.
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