Good grounding practices
Why we ground, and resistance specifications.
By William L. Mostia, Jr., P.E.
Nov 13, 2018
Grounding can be the ultimate common cause due to its ubiquitous nature of connecting
everything electrical together, and a great unknown because much of it and its operation are
invisible to us. This article discusses what makes up a good instrument grounding system and
why. It doesn’t cover all the details about instrument grounding systems (which would take a
book or two), but rather some of the basic principles that lead to good practices, as well as their
technical basis.
First, we must divide the instrument systems into the incoming power side, which is nominally the
AC side, and the instrument side, which is nominally the DC side (Figure 1). The DC side can
be further divided into the DC power side (nominally 24 VDC), control and signal. The AC and
DC power sides are normally isolated through transformers, while on the DC side, the power and
signal are shared. Our discussion will be primarily about the DC side, but for reasons described
later, the grounding system is typically shared by both sides.
Power and ground
Figure 1: Instrument systems can be divided into the AC side and the instrument side, which is
nominally the DC side. The DC side can be further divided into the DC power side (nominally 24
VDC), control and signal. The AC and DC power sides are normally isolated through
transformers, while on the DC side, the power and signal are shared. The grounding system is
typically shared.
Why we ground
The main reasons we ground our systems are:
1. Personnel safety,
2. Electrical system protection,
3. Lightning protection,
4. Electrostatic discharge protection,
5. Electrical noise control,
6. Intrinsically safe circuits,
7. Power quality, and
8. To provide a reference plane for our electrical and electronic circuits and systems.
Personnel safety: This is primarily a concern on the AC (high-voltage) side of the instrument
system. Maintenance personnel test and repair instrument systems, and the operator may also
interact with the instrument system’s front end and field instruments. Because of the low voltage
(nominally 24 VDC), the instrument side is often worked without concern about electrical shock.
An instrument tech may be in for a rude surprise, even a fatal one, when working on an
instrument circuit where an ungrounded DC instrument circuit has come into contact with a
higher voltage source (e.g. 120 or 277 VAC) that didn’t trip the high-voltage circuit
overcurrent protection.
The National Electrical Code (NEC) Article 250 and other application-specific NEC articles
provide requirements for grounding for personnel safety. This is a U.S. code, also known as
National Fire Protection Association (NFPA) 70, which is used worldwide. However, each country
or legal identity may have their own electrical code, or provide additional requirements to the
NEC. You can’t take exception to requirements of the NEC or similar codes just because the
system is an instrument system, not an “electrical” system. Equipment grounding and bonding
are used to help ensure that there's a low impedance path back to the source during the fault
conditions. This allows the system overcurrent protection to open up, protect the electrical
system and remove dangerous voltage from the circuit in a timely manner.

Common codes and standards for grounding for personnel safety are:
NFPA 70, National Electric Code (NEC), Article 250 and specific application articles.

IEC 60364, Electrical Installations for Buildings, Part 5, Section 54

IEEE 142 Std. – IEEE Recommended Practice for Grounding of Industrial and Commercial
Power Systems (commonly called the Green Book)

IEEE Std. 80 - IEEE, “Guide for Safety in AC Substation Grounding”
Electrical Instruments in Hazardous Locations by Ernest C. Magison has an excellent chapter
human electrical safety. Soares' "Book on Grounding and Bonding" is an excellent general
reference on grounding and has a chapter on grounding of electronic systems.
Electrical system protection: The NEC also provides requirements for electrical protection to
limit the damage to equipment and wiring. This is also safety-related as it minimizes the potential
of a fire caused by an electrical source. A properly designed grounding system for the AC side of
our instrument system can minimize the potential damage to equipment from an electrical fault,
surge, lightning strike, etc., and contribute to the reliable operation of the equipment.
Common codes and grounding standards for this are essentially the same as those for electrical
safety given above. NEC Article 250-50 also requires that all grounding electrodes that are
present at each building or structure served shall be bonded together to form the
grounding electrode system (commonly called a ground grid in petrochemical facilities).
This has given rise to the one of the most controversial aspects of grounding—whether it is wise
or necessary to connect the DC side of the instrument system to that noisy, nasty
electrical safety ground. In the early days of DCS systems, manufacturers commonly called for
an isolated, clean ground. This requirement has for the most part been superseded, but still
raises its ugly head occasionally, both as a manufacturer’s requirement and in questions raised
on various Internet forums. The answer to the question by NEC is a solid “yes.” Later, we'll talk
about why this is actually a good idea, as well as the fact that there is no such thing as a “clean”
ground.
Lightning protection: Lightning is always a concern for instrumentation systems, and
increasingly so with new technology that has ever-smaller-dimension digital circuitry, smaller
signal-to-noise ratios, and tighter common mode specifications. These make our digital
instrumentation more sensitive to lightning, RF generation, induced currents and power quality
disturbances.

The common standards applied to lightning protection are:
NFPA 780 – “Standard for the Installation of Lightning Protection Systems”

API 2003 – “Protection Against Ignitions Arising out of Static, Lightning, and Stray Currents”
Electrostatic discharge protection: This is primarily a concern in handling, touching or being in
close proximity to digital electronic chips and cards. Analog electronics are not as sensitive.
Standard manufacturer’s recommended grounding practices for handling digital equipment
should be followed. It's also common practice for raised-floor installations to specify a resistivity
for the floor tile or a resistance to ground. For example, IBM specifies no greater than 2 x 1010
ohms to the ground reference. ANSI/ESD S20.20 has a specification of ≤ 1 x 109 ohms. As you
can see, a little ground goes a long way when dealing with static electricity, but it's a
necessary consideration. This is normally satisfied by specifying the proper floor tile, designing a
good floor stringer grounding system, and using grounding wrist straps when needed.
Static electricity can also generate radio frequency interference (RFI) that can interfere with the
operation of instrumentation, with lightning being the extreme case. I'm aware of a control room
installation where the operator’s chair seat backing crinkled as the operators adjusted
themselves in their chairs, which generated small static electricity discharges and generated RFI
that interfered with their control displays.
Table 1: Noise coupling types
Electrical noise control: Noise is any electrical signal present in a circuit other than the desired
one. All electrical and electronic circuits have noise, which becomes interference when it has an
undesirable or detrimental effect on the operation of a circuit or system. Always a concern in
instrumentation and electronic systems, noise is not as significant in electrical systems (though
modern electrical equipment often has digital monitoring and communication systems).
A common refrain is that ground is a place to drain your noise. The ground is not a sump for
noise, and can actually be a source of noise. A basic principle of circuit electricity is that
electricity always seeks to return to its source. This principle applies to noise: once coupled into a
circuit, noise always works in complete circuits, and ground can serve as a return path for noise.
Most noise of interest is coupled into the instrumentation circuits by four methods: capacitive,
inductive, radiated or conducted (Table 1). We will talk more about this when we talk about
grounding of shielding.
Intrinsically safe circuits: For facilities that use intrinsically safe (IS) circuits to satisfy the
requirements for instruments in classified hazardous areas, grounding can be an issue for certain
types of intrinsic safe barriers. Zener barriers (Figure 2) require a high-integrity ground to shunt
any dangerous electrical energy. The nominal grounding specification is a maximum resistance
of 1 ohm. The intrinsic safety ground is connected to the plant safety ground grid. For the
intrinsic safety ground, the concept of an equipotential ground plane is important to ensure that
the ground potentials in the intrinsically safe circuit are as equal as we can make them to prevent
a spark due to a voltage differential between circuit parts and ground. Transformer or galvanically
isolated barriers typically do not require a ground connection.
IS Zener barrier
Figure 2: Zener barriers in intrinsically safe (IS) systems require a high-integrity ground with a
maximum resistance of one ohm. The concept of an equipotential ground plane is important to
prevent a spark due to a voltage differential between circuit parts and ground.

The standards for intrinsic safety are:
ISA RP 12.06.01, “Recommended Practice for Wiring Methods for Hazardous (Classified)
Locations Instrumentation Part 1: Intrinsic Safety”

ANSI/ISA 60079-11 (12.02.01) – “Explosive Atmosphere – Part 11: Equipment protected by
intrinsic “i””

NEC Article 504 – “Intrinsic Safe Systems”
Power quality: A stable ground reference is important for power quality, particularly with
distributed control systems. Good grounding practices are also necessary for surge protection
devices to work properly. Following the grounding practices of the NEC and the IEEE std.1100,
“Recommended Practice for Powering and Grounding Electronic Equipment,” commonly called
the IEEE Emerald Book, will help achieve good power quality and good grounding
engineering practice.
Circuit reference plane: Grounding is also used to establish a common, stable voltage
reference, so complex and sometimes widely distributed instrument systems can understand
each other’s signals. Circuits work much better if they have a common reference between them.
Common ground
Grounding can be a technically difficult subject primarily because of its complexity (breadth of
scope, infinite number of potential connections, internal and external actors and bad actors, etc.,)
and its uncertainty due to invisibility (can’t see what is going on below the surface, the ground is
different anywhere you look, unknown influences, limited available models that can help the
practicing engineer, etc.). It also can raise the specter of many electrical engineers’ least favorite
subject—electromagnetic fields and Maxwell’s equations—when circuit theory isn’t enough.
Fortunately, much of the basics can be understood by analogy and a bit of circuit theory. This
can lead us to some good engineering practices in regards to grounding instrumentation
systems.
We discuss three topics that commonly arise when engineering instrument grounding. The first is
here and the others are in Part 2:
1. What should the ground resistance be?
2. Do I have to connect my clean instrument ground to that dirty power ground?
3. Do I connect my shields to ground at one end or both?
What should the ground resistance be?
A common grounding question is what the ground resistance should be for a DCS/PLC system
(this question applies to the DCS/PLC ground prior to any connection to other
grounding systems). The National Electric Code Article 250.53 specifies that a second ground
rod is required if the resistance of a single ground rod is greater than 25 ohms. The various
DCS manufacturers have a recommend resistance range from one to five ohms. Communication
sites specifications are typically on the order of five ohms or less.
The question also arises as to whether we should be concerned about impedance rather than
resistance. For instrument systems that have high-frequency components in the ground circuit,
impedance is generally a concern for the above-ground part of the ground system as conductors
tend to change from resistors to inductors as the frequency goes up. It is not as much a concern
for the below-ground part of the instrument ground system.
Table 2: Recommended grounding resistance
Lightning has high-frequency components, and the response of the overall ground grid is
impedance-driven, which should be taken into account in the design of the power ground grid. A
common engineering specification for a DCS is one ohm or less to ground. There is, however, no
technical reason why a DCS system will not operate at a higher ground resistance. For example,
a DCS will operate correctly if it's been constructed on top of rock.
In general, you should make every attempt to meet the manufacturer’s recommended ground
resistance specification. If this is not possible, the DCS ground should be equal to or better than
the associated power system ground resistance specification. Various grounding resistance
specifications are given in Table 2.
Testing of grounds to determine resistance is beyond the scope of this article. Testing the
instrumentation ground prior to connection to the main power grounding grid, using traditional
means such as the “fall of potential” or three-point method, is generally adequate. Some designs
have a switch for testing purposes on the connection line between the instrument ground and the
system power ground grid with a spark gap around the switch for safety purposes.
There are some good primers on earth resistance testing by Megger, Fluke and Aemc. It's
recommended that the tester use a AC test current source. You should not try to use a clamp-on
ground tester for the initial test, but it can be used for subsequent checks after connecting to the
main power grid and doing a benchmark test. The clamp-on ground tester is an excellent tool for
determining if grounding has degraded by comparing readings to an initial benchmark.
It can't be overstressed that a grounding system must maintained, which means that it has to be
periodically inspected and tested. This also applies to the power system ground grid that it’s
connected to. If you let your grounding system degrade, you're asking for trouble, and not just
from an instrument system perspective, but from an overall electrical perspective, too.
That “dirty” power ground
In the past, there was a common refrain by manufacturers and some engineers, and it’s even heard
sometimes today, that they want a “clean” or “quiet” ground for their equipment. When asked to quantify
what such a ground is, they generally talk about a ground not connected to that dirty, nasty power ground.
It seems they expect that noise or problems will somehow arise out of the ground and strike down their
equipment.
This is basically a question of whether to have a separate, isolated (hence somehow clean), instrument
ground, or to have it a part of the overall facility grounding grid.
A perfect ground would never vary in potential—zero potential anywhere (potential because it is singleended, unlike voltage, which is double-ended, or a potential in reference to another potential). This
theoretical ground would also have zero impedance—current flowing to ground would encounter no
resistance, and anything connected would always be at the same ground potential.
Unfortunately, we are stuck with the Earth, which is everywhere that our instrument systems are, and our
instruments can be significantly geographically distributed. This earth can be defined at any single point as
the zero reference potential point of out instrument system, but it will be different anywhere else. The socalled clean ground, isolated from the rest of the grounds (but subject to many of the underground events
that the other grounds are subject to) can the very source of the problems we wished to avoid.
Under quiescent conditions, such a ground may have less variation in ground potential, but under nonquiescent conditions, it can be subject to considerable variation relative to other ground systems. One
should remember that ground is not a sink for noise, but can be a path for it if the ground completes a noise
circuit. Conducted noise flows in complete circuits, and Ohm's Law (impedance version) applies to
conducted noise.
A ground is a ground, or is it?
The essential trouble with grounds is that they are all different. When I was young engineer, I attended a
grounding course put on by Longview Power and Light. As part of the course, there was a field
demonstration where we were shown two ground rods about 50 feet part. A wire was run between the two
ground wires, and a clamp-on ammeter was clamped on the wire. Low and behold, a current was measured
between the two ground rods. The fact that a current was flowing indicated a potential differential between
the two grounds—the grounds were not the same. This small epiphany provided the spark for a lifelong
interest in grounding.
So why are the grounds different? The first difference might be due to different resistivity and, in some
cases, different impedances in the earth. This can be due to different soils, non-conductors like rocks and
voids, moisture content, salt content, ground water, underground artifacts (like pipelines), etc. It can also
be due to the weather and seasonal changes. The current drought is affecting our grounding systems by
drying out the soil, shrinking soil away from ground rods, and reducing the level of ground water.
Figure 1
Courtesy of:
GeoModel, Inc.
750 Miller Dr., SE, Suite B-3
Lessburg, VA 20175
www.geomodel.com/home
The resistivity of the earth is three-dimensional—it has length and width as well as depth. Figure 1 show a
resistance mapping of the earth from a side view. From this one might infer why grounds can be different.
The second reason a ground can be different is that there are currents flowing in the earth, some manmade, others caused by nature. Man-made currents can be transient in nature, like ground fault current
returning to its source through the ground, or continuous, like the currents induced in the ground by our
high-voltage power distribution systems, electric trains, stray currents, or circulating ground currents
caused by poor grounding.
Nature is also a big cause of ground currents flowing in the earth. An obvious source is lightning, which
causes a large, rapid charge redistribution that results in currents flowing and changing ground potential.
Figure 2
A good analogy of a lightning strike to earth is dropping a large rock in a pond and watching the ripples
spread out. This is illustrated in Figure 2. By several estimates, there are about 2,000 thunderstorms
worldwide providing 100 flashes per second (not all of these are ground strikes).
Figure 3
But we don’t need lightning strikes to cause current flow in the earth, we only need a moving thunderstorm
and in some cases just moving clouds (try Googling “clear sky lightning”). Clouds become charged and
can induce currents in the earth. Think about this happening in a global sense all around us. Figures 3 and
4 are illustrations of a moving thunderstorm.
Figure 4
Lightning can also induce currents in the ground and generate RF interference, as shown in Figure 5.
Figure 5
There are other currents in the earth such as geomagnetic currents that result from space weather
interacting with the earth’s magnetic fields, inducing currents on long conductors like power lines and
buried pipelines. These currents are also called Telluric currents.
Figure 6
Some further analogies may help to help better understand grounding. A good analogy for currents flowing
and earth potential varying is the use of the ocean. The ocean has flowing currents that we cannot see, and
waves varying in height, which can represent varying potential (Figure 6).
If we take the ocean analogy a bit further, we can understand why we want to connect all of our grounding
systems together to create (as much as we can) an equipotential grounding plane for our instrumentation
systems, electrical systems, communication systems and computer systems. IEEE std. 1100 [11] has some
good discussion on the equipotential plane.
Visualize two ships separated by several waves or troughs, but connected to each other by electrical cables
(power, signal, etc.). We will use the analogy that the water height above a theoretical reference point
represents ground potential. So, the ships, relative to each other, could at any time be on a wave or trough
of the same height (same potential), on a wave or trough of different heights (potential difference), or one
ship could be on a wave while the other in a trough (larger potential difference). Since the electrical cables
at one ship are at one potential (wave/trough height), while at the other ship there might be a different
potential (wave/trough height), there might be a large potential difference between the electrical cables and
the local ground. If the two ships are at the same wave height (or equipotential plane), the potential would
be zero.
Figure 7
To illustrate how much potential difference there can be between two ground points, where the resistance
between the points is one ohm and the current from lightning flowing through the earth is 10,000 amps, the
potential difference between those two points is 10,000 volts, which would exceed the nominal arc
overvoltage of wiring of 6,000 volts. This is illustrated in Figure 7.
This brings us to the good reason to interconnect power and instrument grounds. What we want is for our
instrument systems to ride up and down the varying ground potential with the rest of the facility, like a
ship riding up and down on waves. We want to create an equipotential grounding plane that rides up and
down our ground potential “waves” as evenly as possible. Providing this “safe ship” to ride out storms is
extremely important to the reliable and safe operation of our instrument systems.
If we have to connect to another “ship,” we should use isolators or connect using non-electrical means, e.g.
fiber-optics (like ships at sea communicating with each other via blinking signal lamps, sometimes called
Aldis lamps).
Another important concept in instrumentation grounding is that of a low-frequency, single-point ground,
i.e. all ground references are connected to a common ground to minimize any potential differences on the
DC side of our systems. These connections should not be daisy-chained and should provide a lowimpedance path back to our DC ground. This ground should be connected to the power grounding grid at
only one point. Selection of this point of connection should consider the power distribution system (how
large ground faults might occur, and how they will return to their source; smaller leaks return using the
same path), where the lightning protection system is connected to the grounding grid (not too close to the
instrument connection), location of cathodic protection systems (generally, stay away from them), location
of underground pipes (stay away), etc. Figures 8 and 9 show an example DCS grounding scheme and a
ground grid (not to scale).
Figure 8
Figure 9
At higher frequencies, multipoint grounding systems are used because these systems will be grounded
anyway through distributed capacitances, and it is better to separately ground them. Don’t confuse lowfrequency grounding requirements with higher-frequency ones.
Before we leave this topic, we should address ungrounded systems. NEC Article 250 addresses which AC
systems must be grounded. Instrument systems that are powered typically by 12-28 VDC systems are not
addressed. People do often use ungrounded systems for DC instrument loops where they have an isolated
DC power supply or four-wire instrument loop. These loops will function this way and there are
applications where this may be necessary.
There are, however, some potential pitfalls to having such loops:
1. The loop is not referenced to the rest of the instrument system.
2. If it becomes inadvertently grounded at an undefined point, this may affect the operation of the loop in a
negative way.
3. It may not be apparent to an instrument technician that this loop is different from other loops and they may
not understand why their voltage readings are not correct.
4. If the loop inadvertently come into contact with a higher voltage, e.g. 120 VAC, the instrument technician
may be in for a rude surprise, or even a fatal one.
Do I connect my shields to ground at one end or
both?
This question has a life of its own and seems come up time and time again. Shielding is a complex subject
that can be very application-dependent. This discussion is primarily directed at shielding in petrochemical
plants.
The purpose of shielding is to keep noise in or to keep noise out of a circuit, more toward the latter than the
former. Noise can be defined as any unwanted electrical signal in a circuit, while interference is noise that
has a detrimental influence on the circuit. To understand shielding and the related question of grounding
shields, we must understand how noise gets into a circuit. Noise can also be generated internal to the
circuit, in which case, shielding is not much help except to keep it from getting out of the circuit.
There are four basic means that noise is coupled into a circuit: capacitively, inductively, radiated and
conducted. The frequency of the noise and the operating frequency of the circuit must be considered. Most
instrumentation measurement and control circuits operate at low frequency (< 100 Kbits/s) or at DC, while
most communication circuits operate at high frequency (> 1 Mhz). This typically results in different shield
grounding methods for low frequency (grounded at one end) than at high frequency (grounded in multiple
places). Here, we discuss low-frequency grounding.
Figure 10
Shielding capacitively coupled noise: Capacitive or electrostatic coupled noise is coupled through
distributed capacitances formed between the source of the noise and the receptor (or victim) of the noise.
This type of noise is voltage-based (Figure 10).
We shield against this type of noise coupling by placing a grounded shield (at the system reference
potential) between the noise source and the receptor circuit to provide a conductor for the distributed
capacitances to connect to rather than the signal conductors. This normally takes the form of a thin,
aluminum-coated Mylar film with a drain wire running the length of the shield around the protected wires
(Figure 11) Any noise capacitively coupled to the shield is returned to the source via the shield ground
connection. If the shield impedance is zero, the noise does not couple to the protected signal wires since it
has been intercepted by the shield at zero potential relative to the signal wire reference.
Figure 11
In practice, the shield impedance is not zero and there will be some noise voltage generated across the
shield and coupled to the signal wires, but it’s greatly reduced from the unshielded cable. This shield is
grounded at one end at the zero potential reference point of the circuit (nominally the DC ground reference
point). This is typically done in the main or master termination boxes in the DCS/PLC equipment room.
The shield continuity is maintained through any marshalling and field junction boxes out to the field
device, where the shield is folded back and taped or heat-shrinked. The only common exception is
grounded thermocouples, whose shields are commonly grounded at the thermocouple head or the field
junction box closest to it.
The reason we ground at one end is that our field devices can be a long distance from the receiving
element and try as hard as we can, we will still have differences in ground potential. If we connect at both
ends, we can have circulating currents in our shields. This can be particularly detrimental during ground
disturbances.
Some keys here are to make sure you do a good job of terminating the shield in the field so it can’t come
into contact with ground or something that is grounded; run your shields as close as you can to any
termination points; and keep your exposed drain wires as short as possible.
Figure 12
Shielding of inductively or magnetically coupled noise: Shielding against inductively or magnetically
coupled noise is a bit more difficult. This noise is coupled or induced by a varying magnetic field similarly
to how a transformer works. This noise is current-based—the higher the current at the source, the more
noise is coupled at the receptor. This type of noise is illustrated in Figure 12. For this, the aluminum shield
is no barrier and for a metallic shield to be successfully, it must be made of a ferrous material. However,
connecting the shield at both ends can provide some protection against magnetically coupled noise by
inducing a counter current on the shield to the noise current coupled to the signal wires. That said, we still
have the problem that if we connect our shields at both ends, we will have circulating currents in our
shields from other sources besides our magnetic coupled noise. In addition, the aluminum shields used in
our typical shielded, twisted-pair cables are not designed to be current-carrying conductors and in the
extreme case, you may burn through your cable. Some people have been successful in grounding the other
end of the shield through a capacitor to provide solidly grounded shield at one end at DC and a varying
impedance at frequency, grounded at both ends through the capacitor.
If the cable is contained in the same building and both ends share a common equipotential plane, you may
be able get away with grounding the shield at both ends, but it is a last resort for process instrumentation
systems. It’s commonly done to get rid of hum in audio systems, however, they typically meet the abovementioned limitations. And bear in mind, though it’s not grounding, twisted-pair is an effective means of
reducing magnetically coupled noise, as is differential inputs in 4-20 mA circuits.
In summary, the correct practice is to ground your shields at one end, at the zero-potential reference point
of the circuit.
Radiated noise: Radiated noise protection isn’t generally about grounding since it is a function of
reflection and absorption, which do not require grounding to work. Radiated noise can be picked up by
“antennas” in the construction of the equipment that are “tuned” to the radiated noise wavelength. Once in
a circuit, this noise behaves like conducted noise. It is good practice to specifically ground your field
junction boxes. “Noise Reduction Techniques in Electronic Systems” by Henry W. Ott has a good
discussion on this.
Conducted noise: Conducted noise is noise that has gotten into a circuit by various means and has been
successfully conducted past its entry point. Often, this type of noise is filtered out by means that include
shunting the noise through ground back to its source. A good ground system is a key to doing this
successfully.
Conclusions
The basic principles of a good instrument system can be summed up as:
1. A well designed and maintained plant ground grid is priceless. Follow the standards.
2. A well designed grounding and bonding system is key to reliable operation of your instrument system.
3. Follow your control or instrument system manufacturer’s recommended ground resistance where possible.
In lieu of such a recommendation, as a minimum, keep your instrument ground resistance to less than 5
ohms where possible.
4. Connect your DC instrument systems to a single point ground, and connect this ground to the plant ground
grid at only one point.
5. Inspect, test and maintain your ground systems.
6. Connect your shields at only one end.
About the author:
Frequent contributor William (Bill) L. Mostia, Jr., P.E., fellow, SIS-Tech Solutions, can be reached
at wlmostia@msn.com.
References:
1. NFPA 70 (NEC), “National Electric Code,” National Fire Protection Association, 1 Batterymarch Park,
Quincy, MA, www.nfpa.org
2. IEC 60364, Electrical Installations for Buildings, Part 5, Section 54, International Electrotechnical
Commission, Geneva 20 – Switzerland, www.iec.ch
3. IEEE 142 Std. – IEEE Recommended Practice for Grounding of Industrial and Commercial Power
Systems (commonly called the Green Book), Institute of Electrical and Electronic Engineers, New York,
NY, www.ieee.org
4. IEEE Std. 80 - IEEE guide for safety in AC substation grounding,” Institute of Rev. 1 - 7-15-13 Electrical
and Electronic Engineers, New York, NY, www.ieee.org
5. NFPA 780 – “Standard for the Installation of Lightning Protection Systems,” National Fire Protection
Association, 1 Batterymarch Park, Quincy, MA.
6. API 2003 – “Protection Against Ignitions Arising out of Static, Lightning, and Stray Currents ,“ American
Petroleum Institute, Washington, DC, www.api.org
7. IBM Power7 Information – “Static electricity and floor resistance,” IBM Corp.
8. ISA RP 12.06.01, “Recommended Practice for Wiring Methods for Hazardous (Classified) Locations
Instrumentation Part 1: Intrinsic Safety,” International Society of Automation, Research Triangle, NC.
9. “All you ever Wanted to know about lighting,” http://www.coursealert.com/22.html
10. The Lightning Discharge, Martin A. Uman, Dover, 1987
11. IEEE std.1100, “Recommended Practice for Powering and Grounding Electronic Equipment,” (commonly
called the Emerald Book). Institute of Electrical and Electronic Engineers, New York, NY, www.ieee.org
12. “Integrated Production Control System CENTUM VP System Overview (Vnet/IP Edition),” Yokogawa
Electric Corporation, GS 33K01A10-50E GS, pg. 17, 2011.
13. “Site Design and Preparation for DeltaV_ Digital Automation Systems,” D800015X052, pg. 4-7, Emerson,
September 2005.
14. “Data Hiway Planning,” DH02-501, Pg. 103, Honeywell, 9/95.
15. “STANDARDS AND GUIDELINES FOR COMMUNICATION SITES,” 68P81089E50-B, Motorola,
Pg. 4-47
16. Soars Book on Grounding and Bonding, 9th Edition, International Association of Electrical Inspectors,
Richardson, Tx, 2004.
17. Electrical Instruments in Hazardous Locations, 4th Ed., Earnest Magison, ISA, 1998.
18. “Notes on Substation Grounding,” Jeff Jowett, Megger
19. “A practical guide to earth resistance testing,”
Megger, http://www.megger.com/us/story/Index.php?ID=146
20. Grounding “Principles, testing methods and applications,” Fluke
Corporation, http://support.fluke.com/find-sales/Download/Asset/2633834_6115_ENG_A_W.PDF
21. “Understanding Ground Resistance Testing,”
Aemc, http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBKGROUNDWEB.pdf
22. Grounding and Shielding Techniques in Instrumentation, 3rd Ed, Ralph Morrison, Wiley-Interscience,
New York, NY,1986.
23. Noise Reduction Techniques in Electronic Systems, 2nd Ed., Henry Ott, Wiley Interscience,New York,
NY,1988.
24. Grounding and Shielding in Facilities, Ralph Morrison & Warren H. Lewis, Wiley-Interscience, New
York, NY, 1990.
25. Grounding and Bonding, Volume 2, Michael Mardiguian, Interference Control Technologies, Inc.,
Grainesville, Va, 1988.
26. Practical Grounding, Bonding, Shielding, and Surge Protection. G. Vijayaraghavan, Mark Brown, &
Malcolm Barnes, Elsevier, Burlington, Ma, 2004.
27. ANSI/ISA-60079-11 (12.02.01)-2011, “Explosive Atmospheres – Part 11: Equipment protection by
intrinsic safety “I”, International Society of Automation, Research Triangle, NC.