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1.3 Grounding Problems:
Background
A poor ground system can cause severe electrical problems. Electrical control
systems can experience both over voltage and voltage sag conditions due to a
poor ground. This can cause nuisance shutdowns, damage to power supply
circuits, communications errors, and even be a safety hazard for fault conditions.
Electrical fault conditions must have a low resistance path to earth ground. The
ground conductor supplied to the machine should be sized and installed per NEC
and any additional local wiring requirements. The utilization of metal conduit or
air piping that is attached to the air compressor is not considered an adequate
ground.
Typically, building codes require that structural steel must be grounded per NEC.
Structural supports such as steel girders and beams should be electrically
attached to earth ground via a buried grid. Verify the supplied ground wire meets
ampacity requirements per code and that it connects to the approved building
earth ground grid.
Some environments may have a distorted or noisy ground. This is usually an
indication that current is flowing into earth ground. This can be caused by faulty
electrical equipment in the area that is attached to the ground grid. Ground
currents can be present in environments that utilize variable speed inverter type
motor drives, such as variable frequency drive (VFD). Environments that utilize a
large number of switching power supplies can also cause ground currents. Most
all computer systems use switching power supplies. Many of these ground
currents can be generated by high frequency (above 60 HZ) disturbances that
are known as harmonic distortion. Because of the high frequency, they are hard
to analyze and measure. An effective safeguard against this type of ground
current is to minimize the length of wire to the ground grid. The use of braided
ground wire minimizes high frequency distortion. If braided wire is not available,
then standard stranded wire can be used if ampacity of wire is increased to 3X
the rated value.
Verify the ground grid point is free from corrosion or moisture that may prohibit a
low resistance ground. It is important to verify that other electrical equipment that
is electrically bonded to the air compressor is properly grounded as well. This
will include any electrical device that is structurally connected to conductive air
piping/plumbing originating at the air compressor. Wired interfaces such as
remote start/stop, remote starters, sequencers, sequencer interfaces, Intellisys
Sequence Control, Intellisys Remote Interface should also be properly grounded.
Procedures
A practical way to measure the ground current is to use an ammeter:
Externally induced ground current (noise), power off state:
A Fluke 87 or equivalent meter can be used to measure ground current.
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