Spirit II User’s Manual
Section 3: Installation
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Radio Frequency (RF) and
Electromagnetic Interference (EMI)
Overview
This section describes the proper grounding of the Spirit II Plasma System components
to minimize Radio Frequency (RF) and Electromagnetic Interference (EMI).
The Arc Starting Console (ASC), by nature of its function in the system, is a source of
RF/EMI along with other system components such as drive amplifiers. If proper
grounding techniques are not employed during system installation, RF/EMI can couple
into other components causing system malfunction and/or component failure. While this
section outlines best practices for grounding, this does not guarantee system immunity.
These guidelines should be the basis for initial installation and modifications made as
necessary to achieve complete immunity.
Types of Grounds
There are three different types of grounds in a plasma system.
1. Service or Protective Earth (PE) ground. This is the ground associated with the
mains power supplied to the system. The purpose is to prevent a shock hazard with
respect to the plasma equipment and work table. It represents the service ground
connected to the plasma power supply and all other system components such as
drive amplifiers and CNC. The PE or Service ground must be connected to each
piece of equipment per local and national codes.
2. DC power ground. This is the work lead of the power supply and is connected to the
cutting table to complete the electrical path for the cutting current.
3. RF/EMI ground. This is the ground for limiting RF/EMI noise in the system. This is
the ground that this section addresses.
RF/EMI Grounding Rules
1. The cutting table is used as the common star grounding point. All RF/EMI grounds
should terminate at this point. The star ground connection to the table should have
welded studs to the table with a copper bus bar mounted to them. All hardware
used for ground connections should be copper or brass with exception of the studs
welded to the table.
2. A ground rod that meets all applicable local and national electrical codes must be
installed within 20 ft. of the star ground point. This is the PE ground and should be
connected to the star ground with a minimum of a 6 AWG green/yellow cable.
3. The work, electrode and pilot arc leads from the power supply should be bundled
together for as long a distance as possible and segregated from control leads.
Ideally the power and control leads should run in separate cable tracks – if not, a
minimum separation of 6 in. is recommended.