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Integrated Earth Systems

THE basis for “Safety & Security”

Presented by:

Rob Kersten

© 2010 MIW Consultants

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Executive Summary

� Safety & security of electronic systems, is essential for

all organizations

� Organizations can be put in a very vulnerable position

when their processes are interrupted

� Proper earthing is one of the elements, fundamental

for the stability of electronic systems

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Overview

• Introduction

• Safety First!

• Earthing (grounding) history:

- Electrical power distribution systems

- Earthing

- Safety and EMC

- Lightning protection, safety and EMC

• Conclusions

• Questions

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Introduction

• My first job was with NCR; here I was responsible

for the first computers at the DNB, RPS etc.

• The next challenge was found with Foxboro (today

Invensys) in Industrial Automation. Via service,

hardware- system- and network- design, I became

their global consultant with the nick name:

Mr. Power & Grounding

• I’ve established MIW Consultants in 2008See http://www.miwconsultants.nl/ for further details

• Board member of the Dutch EMC-ESD Society

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Safety First!

This is NOT a “Safe Voltage Area” in a humid-, medical- or

explosive- (ATEX) environment etc.

Supposed

Safe

Voltage

Area

Safe

Voltage

Area?

50 Vac 110 Vdc

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Earthing (Grounding)

• Earth connections are required for:

- Protective earth (PE) = Safety

- Functional earth (FE) = Security & Reliability

(EMC, shielding, electronic reference)

- Lightning protection = Safety & Security & Reliability

- ESD = Reliability thus also Safety & Security

- Etc.

• Design-, installation- and maintenance- engineers must

master ALL these disciplines (previously different

companies with different engineers)!

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LEMP (Lightning Electromagnetic Pulse)

Benjamin Franklin

Lightning is dangerous for people, animals, electric- and

electronic-circuits.

Benjamin Franklin invented the lightning rod in 1749 during his

famous kite experiment when he could no longer wait until

completion of a church tower equipped with his lightning rod

and down connector to earth.

The American NFPA demanded a sharp lightning point on the

rod (Franklin’s invention), but rivaling United Kingdom insisted

on a blunt (rounded) version. Experiments by the American

scientist C.B. Moore unveiled in 1999 (251 years later!) that the

hit probability of Franklin’s rods improved considerable when

making the sharp top blunt.

Safety ???

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Electrical Power Distribution Networks

Thomas Alva Edison

Much of the American industrial revolution took place in New England.

Only a few people remember the technological breakthrough in the

early 1880’s in the north eastern place Brockton Massachusetts with

the first electrical power distribution network.

The various electrical power distribution networks evaluated from the

pioneering work at that time.

The biggest challenge:

- Obtaining personnel- & fire- safety

- Finding reliable insulation materials

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Energy Distribution Networks

The various earthing concepts of energy distribution networks aredefined in IEC 60364:

ITThe power source is floating (not earthed). Metal enclosures and structures are locally earthed with a PE conductor.

TN-SThe neutral is earthed at the energy source. Metal enclosures and structures are earthed with a PE conductor between energy sourceand connected loads. TN-CSThe neutral is earthed at the energy source. Metal enclosures and structures are earthed with a combined Neutral and PE conductor between energy source and connected loads.

TT

The neutral is earthed at the energy source. Metal enclosures and structures are locally earthed.

NOTE 1: These energy distribution networks provide safety when correctly designed, installed and maintained

Note 2: Other characteristics differ considerably (i.e. EMC).

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TN-S Energy Distribution Networks

The TN-S energy distribution network has the best EMC characteristics for industry.

The intended current flows entirely through the line (L) en neutral (N) conductors. The

primary function of the protective earth conductor (PE) is safety, but is also an efficient

(low impedance) return path for interference currents from line filters and surge

protective devices, without the disadvantages of the TN-CS network.

L

N

PE

U = U2

(Identical conductors)

E

Re

NE 98

4. Network types

(TN and IT nets)

“TN” and “IT” nets are usual today

for three-phase systems in

installations where low power supply

is involved. Differing consequences

are involved for

recommended EMC measures,

depending on the network type

utilized. TN-S nets are more practical

from an EMC perspective and

therefore preferable.

First price

for EMC in

de industry!

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Electrical Interference (EMI / RFI)

Guglielmo Marconi

Made the first public transmission of wireless signal in 1896 using a

spark – technology. This EMI / RFI interference generating technology is

strictly forbidden today! This solution was less efficient then the carrier

wave (CW), but it took long for King Spark’s invention to disappear.

The negative EMI / RFI characteristics of wanted and unwanted radio transmission signals

became obvious; control of the radio frequency spectrum was soon a necessity! IEC

recommended to establish CISPR (1933) tasked to address the increasing problem of

Electromagnetic Interference. CISPR published technical documents about metrology,

test procedures, emission- and immunity requirements, also for unintended transmitters

(i.e. digital equipment).

CISPR = Comité International Spécial des Perturbations Radioélectriques = part of IEC

EMI = Electromagnetic Interference

RFI = Radio Frequency Interference

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Interference Mitigation

The telephone industry was probably the first needing interference

mitigation, because de-energizing relay coils caused arcing (from back

EMF) across relay contacts. This arcing resulted in unwanted clicking

noises on the audio signals.

Fundamental understanding developed here about:

• Conductor impedance

• Interference coupling via a common impedance

• Undocumented inductive and capacitive coupling between circuits

• The importance of segregation between signal- & power- wiring

• The “Zero Signal Reference Plane”, an earthed copper plate under a

telephone exchange

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Process Industry

Last century, the process industry evolved gradually from pneumatics, via

analog & digital circuits to computer driven control- en safety systems.

Electronic systems are sensitive to excessive interference causing costly

production losses. The process industry invested a lot of money to prevent these

unwanted losses, for example by creating independent “island systems” with

separate earth connections like:

PEclean , FEanalog , FEdigital , FEshield , FE-IS.

Reliability was originally acceptable, but more and more problems developed

over time, like:

• Electrocution risk by touching different earth networks simultaneously

• Explosion risk due to potential differences (arcing)

• Component damage after (indirect) lightning hits

• Shortage of specialists capable to maintain these tricky solutions

Yes, 5 Earth's for one system!!!!!

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Typical classical “Island System”

Ultra Isolation Transformer

“Fenced” Island

HF Choke

Clean Earth

Not for new designs!

Functional Earth

Safety Earth

HF Choke20 µH

1.5 mOhm25 mm²

Utility PowerProtective Earth (PE)

UltraIsolation

Transformer

Dedicated Earth

Soil (Earth) Surface

Isolated & Shieldedbelow PE and atleast 4 m below

surface.

PE Earth Rod(s)Impedance <

Dedicated Earth

Dedicated Earth Rod(s) Impedance < 2 Ohm

Minimum distance equals length of longest rod

Feeder 1

Feeder n

N L E

Comm.Electronics

N L E

ProcessorElectronics

N L E

Isolated I/OElectronics

Feeder 2

Run Dedicated Earth- and Signal cables in close proximity

Ns LsEs

Np LpEp

Dedicated Power

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The Result : Chaos on EARTH !

Earth Computer EarthMother Earth Dirty Earth

Plant Earth Instrument Earth Separate Earth Structural Earth

Clean Earth

Digital Earth Safety EarthAnalog EarthPower Earth Ground

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THE Solution: Regulations & Directives

• USA - FCC since 1979

• EU - EMC Directive since 1989

• EU - CE mandatory for EMC since 1-1-1996

• EMC � Reliability � Safety � Security!

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Solution: Safety and EMC

IEC/TR 61000-5-2 (1997)

Clear guideline for installations :

• How (not) to earth

• How to obtain optimal EMC behavior

WRONG WRONG GOOD

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Why are all these interconnections so important?

• They provide Safety (reduced

step and touch voltages)

• They reduce the impact of

lighting hits = Security

• They reduce EMC problems

caused by normal- and common-mode

interference = Reliability

Solution: Safety and EMC

IEC/TR 61000-5-2

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What is Normal- and Common-Mode Interference?

Input Channel

Thermo-couple

ElectronicsEarth

Connection

InterferenceSignal

The earth

Short or stray capacitance

Input Channel

Thermo-couple

ElectronicsEarth

Connection

InterferenceSignal

The earth

Common Mode (CM) Interference

• Caused by potential differences

between source and destination

• Earth connection may be real or

due to stray capacitance

• Different earth connections have

different potentials

Normal Mode (NM) Interference

• Mostly caused by Electromagnetic

fields

• Circuit asymmetry causes CM to

NM conversion

Solution: Safety and EMC

IEC/TR 61000-5-2

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Why are all these interconnections so important?

To create a low impedance Signal Reference!

Solution: Signal Reference Structure

Source: IEEE Emerald book / Std 1100 – 2005 section 4.8.5.3

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Solution: Lightning Protection, Safety

& EMC conform IEC 62305 (2006)

IEC 62305 (LEMP) introduced an even further

integrated approach for earthing of an entire

industrial complex!

Lightning earth grids:

Inside building: 5 x 5 m

Around building: 20 x 20 m

Open area: 40 x 40 m

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Solution: Lightning Protection, Safety

and EMC conform EMC IEC 62305

The zoning concept of IEC 62305 is compatible with

the protection levels for Surge Protection Devices

(SPD’s). Hence, the interference potentials can be

controlled for all connected equipment.

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Question:

Is it still important to prevent earth loops?

That differs from case to case!

• Rarely within a PE network

• Sometimes for a cable shield

(i.e. when shield = return conductor)

• Often within the FE network (signal path)

• Always in medical environments!

No black & white answer!

Any Earth System must be engineered!

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Conclusions

� Dedicated earth systems operated reasonably

well until the 1980’s. EMC understanding was still

improving & system clock speed is ever increasing

� Today we generally need the Integrated Earth

System for safety earth, functional earth and

lightning protection!

� The Integrated Earth System is a robust and field

proven technology for Safety and Security

� Remaining dedicated earth systems must be

exclusively maintained / upgraded by specialists

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Thank you, for your attention!

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Questions?

Integrated Earth Systems?

Safety? Security?

Electronic Systems?Availability?

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Disclaimer

The author disclaims liability for any direct, indirect, consequential or incidental damages that may

result from the use of the information, or from the inability to use the information or data contained

within this presentation. Any terms mentioned in this document that are also registered trademark have

not been clearly marked. Therefore, it cannot be concluded from an absent ™or ® marking that a term

is an unregistered trademark. Equally, it cannot be determined from the text if patens or protection of

utility patents apply.

Copy Rights

The author expresses his thanks to the International Electrotechnical Commission (IEC) for permission to

reproduce Information from its International Publication IEC 61000-5-2 (1997) and IEC 62305-4 (2006).

All such extracts are copyright of IEC, Geneva, Switzerland. All rights reserved. Further information on

the IEC is available from www.iec.ch. IEC has no responsibility for the placement and context in which

the extracts and contents are reproduced by the author, nor is IEC in any way responsible for the other

content or accuracy therein.

Citations from other origins are included under the applicable citation rights (i.e. the USA “fair uses

policy”). They underline the importance of the discussed Integrated Earth System. The author expresses

his sincere thanks to their owners.