Safety CountS
To Ground or Not to Ground
That is the Question
Mike Orzechowski
I
t is not always clear as to when to (or when
sible to address every application in this forum.
specific piece of equipment like concrete saw
not to) ground (connect to the earth) a
This article was intended to be a general over-
through the receptacles on the generator. I
portable electrical generator. There are
view of when to ground a generator without
call this the cord and plug system. The other
many factors that influence the decision. It
diminishing the fact that electricity can be
method is to use the generator as a means to
may surprise you to know that sometimes
very dangerous and requires a knowledgeable
supply power, much as the utility company
you should NOT supply an additional ground-
expert (a licensed or qualified electrician) to
would supply power, at a remote location or
ing rod to the generator; sometimes it really
understand and appreciate all the details as-
for emergency power. Typical elements receiv-
doesn’t matter; and sometimes you should
sociated with each application.
ing power in this case would be a complete job
ground your generator. So it is important for
Proper grounding and bonding is impor-
you to know the difference so that you can
tant to help prevent shocks and electrocutions.
have your system in a safe operating condi-
You can find information on grounding and
If you are using the cord and plug system,
tion at all times.
bonding in the National Electric Code (NEC) at
typically you do not need to supply an earth-
Portable generators are used to gener-
www.nfpa.org. Your local electrical codes are
grounding rod with the generator. There
ate electricity on a much smaller scale then
probably based on the NEC, but they might
are no other sources of electricity, lighten-
the utility companies. For that reason, they
have some additional requirements that you
ing surges, or fault currents that you would
are ideal for temporary, remote or emergency
should be familiar with.
need to contend with. The housing/frame
site, a trailer, a structure or a house. I call it a
power source system.
electrical service. Depending on how the gen-
In my mind, there are two different ways
of the generator will serve as an adequate
erator is being used, it will need to be properly
to use a generator. The first is as an isolated
ground for the fault currents generated by
wired for the application. It is nearly impos-
system in which the generator is powering a
that particular generator. You will still need
REPRINTED FROM CONCRETE OPENINGS | VOL.17 | NUM.3 | september 2007
to have a grounding conductor running from
the piece of equipment to the generator and
the grounded pin in the receptacle, the neutral
element will have to be properly bonded to
the grounding source at the generator, the
generator housing or frame. In addition, all
of the non-current-carrying metal parts of the
generator and the vehicle or trailer that it is
mounted to must be bonded to the grounding
source, the generator housing/frame. You can
supply a grounding rod if you want for the
cord and plug system, but it is not necessary.
Using a generator as a power source system
to provide temporary, remote or emergency
power for a house, trailer or complete job site
is a much more complicated scenario in terms
of whether or not to drive a new grounding
rod. Either way, the generator used this way
must have the proper earth grounding, for
example, a grounding rod. The generator will
need an additional earth-grounding rod if it is
a separately derived system. If it is not a separately derived system, there is a good chance
you should not have another earth grounding
rod. This is where it gets complicated, and this
is where you must use a licensed or qualified
electrician.
To overly simplify the reason why, you
when or when not to ground a portable elec-
must first understand that the power source
trical generator. For practical applications,
system is wired to a circuit breaker panel by
please remember that electricity can be very
means of a transfer switch. The transfer switch
dangerous and requires a knowledgeable ex-
is simply a means to transfer power from the
pert such as a licensed or qualified electrician
utility power source to the generator. If the
to safely wire and configure the system.
transfer switch only switches the hot, then
The NFPA and OSHA have additional
the generator is not a separately derived sys-
materials on this subject.
tem and must be bonded to the grounding
Visit www.osha.gov, keyword electric or
rod of the utility power at the transfer switch
www.nfpa.org, click on NFPA70 or NEC.
since it can be unsafe to have a potential difference between the two grounding points.
If the transfer switch switches both the hot
and grounded (neutral) conductors, then it is
Mike Orzechowski is the engineering manager at
Equipment Development Company, Inc. (EDCO)
and can be reached at 800-638-3326.
considered a separately derived system and
must have a proper grounding rod in place
for the fault currents such as lightening, line
surges, unintentional contact with other voltage sources or back feeding currents.
“To ground or not to ground, that is the
question.” Keep in mind, that this article is
strictly a guide as to the simple concept of
REPRINTED FROM CONCRETE OPENINGS | VOL.17 | NUM.3 | september 2007