Maintenance Technology September 2017 - 23

PLANT SAFETY MATTERS

Update Your

Grounding
Knowledge
Lives and property are
endangered by incomplete
or outdated grounding
information and lack of
corrective action.

WIDE AVAILABILITY AND strong
historical performance mean electrical
distribution and safety issues sometimes
go unnoticed. Plant managers, however,
must still understand the risks posed
by aging infrastructure and changes to
facilities. Increasing that understanding,
particularly in the area of grounding, is
the aim of a recently released white paper
written by Adele Hostettler and Mark
Thomas of Emerson (emerson.com,
Round Rock, TX).
Writing from their perspective as
technicians with Emerson's Reliability
Services group, the authors focused
on a number of crucial matters and
best-practice approaches associated with
grounding systems, starting with the
crux of the issue: voltage, and its impact
on safety.
Voltage and resistance determine
the amount of current generated in a
circuit. Higher voltage means more
current. Current is the source of
damage to people and equipment. Three
factors determine the level of damage:
amount, path, and duration of current.
Although no action can eliminate the
risks completely, properly installed and
maintained grounding can mitigate
them and reduce the potential for injury,
damage, and expense.
SEPTEMBER 2017

Current is the source of damage to people and equipment. Although no action can
eliminate the risks completely, properly installed and maintained grounding can
mitigate them and reduce the potential for injury, or worse.

A failed grounding system can be
catastrophic on several counts, causing,
among other things:
■ injury or death
■ extreme equipment damage
■ legal and financial risks.
OSHA's general regulation states
employers must provide a safe workplace
and comply with NEC Article 250, which
addresses electrical-system bonding and
grounding. Although few regulations
cover maintenance and testing, any
hazard resulting from an inadequate
design, ineffective testing, or lack of
maintenance can result in severe sanctions and penalties. Because grounding
is primarily for safety, the "grandfather
clause" does not apply.

How grounding fails
Equipment grounds reduce induced
voltages on metal parts from nearby
power lines and distribution equipment,
helping prevent damage from arcing
within buildings/structures. Accordingly,
any equipment with the potential for
static buildup requires grounding. Static

buildup develops due to the friction of
moving material and can happen on
tanks, vessels, and piping. Bonding and
grounding help drain static-electricity
charges before flashover potential is
reached.
Electrical-power systems, such as the
secondary winding of a transformer,
are grounded to limit the voltage
induced by lightning, line surges, or
unintentional contact by higher-voltage
lines. Secondary grounds also stabilize
the return path for single-phase loads.
If the contact resistance of an electrode
to the earth is high, very little fault
current can return by that path, and
the circuit protection device may not
open to clear a ground fault. Then all
metal parts associated with the electrical
installation-metal piping and structural
building steel-could become, and
remain, energized.
Hostettler and Thomas noted that
when plant personnel are evaluating a
grounding system, it is important for
them to remember safe dissipation paths
are determined, in part, by soil composiMAINTENANCETECHNOLOGY.COM | 23
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Table of Contents for the Digital Edition of Maintenance Technology September 2017
