SIST EN 60079-30-2:2018

SLOVENSKI STANDARD
01-januar-2018
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SIST EN 60079-30-2:2007
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Explosive atmospheres - Part 30-2: Electrical resistance trace heating - Application guide
for design, installation and maintenance IEC/IEEE 60079-30-2:2015 (MOD)
Explosionsgefährdeter Bereiche - Teil 30-2: Elektrische Widerstands-Begleitheizungen -
Anwendungsleitfaden für Entwurf, Installation und Instandhaltung IEC/IEEE 60079-30-
2:2015 (MOD)
Atmosphères explosives - Partie 30-2: Traçage par résistance électrique - Guide
d'application pour la conception, l'installation et la maintenance IEC/IEEE 60079-30-
2:2015 (MOD)
Ta slovenski standard je istoveten z: EN 60079-30-2:2017
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 60079-30-2

NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2017
ICS 29.260.20 Supersedes EN 60079-30-2:2007
English Version
Explosive atmospheres -
Part 30-2: Electrical resistance trace heating - Application guide
for design, installation and maintenance
(IEC/IEEE 60079-30-2:2015 , modified)
Atmosphères explosives - Partie 30-2: Traçage par Explosionsgefährdeter Bereiche - Teil 30-2: Elektrische
résistance électrique - Guide d'application pour la Widerstands-Begleitheizungen - Anwendungsleitfaden für
conception, l'installation et la maintenance Entwurf, Installation und Instandhaltung
(IEC/IEEE 60079-30-2:2015 , modifiée) (IEC/IEEE 60079-30-2:2015 , modifiziert)
This European Standard was approved by CENELEC on 2017-04-03. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60079-30-2:2017 E
European foreword
This document (EN 60079-30-2:2017) consists of the text of IEC/IEEE 60079-30-2:2015 prepared by
IEC/TC 31 "Equipment for explosive atmospheres" in collaboration with IEEE Standards Association
(IEEE-SA), together with the common modifications prepared by CLC/TC 31 "Electrical apparatus for
potentially explosive atmospheres".
The following dates are fixed:
• latest date by which the document has to be implemented at (dop) 2018-04-03
national level by publication of an identical national
standard or by endorsement
• latest date by which the national standards conflicting with (dow) 2020-04-03
the document have to be withdrawn

This document supersedes EN 60079-30-2:2007
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC/IEEE 60079-30-2:2015 was approved by CENELEC as a
European Standard with agreed common modifications.
COMMON MODIFICATIONS
NOTE The Division method of area classification of IEC/IEEE 60079-30-2:2015 is not applicable for a European
Standard, because a correlation with the Equipment Categories according to the European Directive 2014/34/EU
is not possible. Consequently requirements for Divisions 1 and 2 and references to NFPA 70 and CSA C22.1 are
excluded from this standard.
1 Scope
Delete the following sentence in the first paragraph:
"This standard also provides guidance for explosive atmospheres incorporating the Division method of
area classification that may be applied by some users of this standard."
Delete the note:
"NOTE Information on the Division method is given in NFPA 70 and CSA C22.1."
4.1 General
Delete the following part of the second sentence in the second paragraph:
"…, and/or the Division 1 and Division 2 explosive atmospheres, …".
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is
available here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-426 -  International Electrotechnical - -
Vocabulary -
Part 426: Equipment for explosive
atmospheres
IEC 60079-0 -  Explosive atmospheres - EN 60079-0 -
Part 0: Equipment - General
requirements
IEC 60079-15 -  Explosive atmospheres - EN 60079-15 -
Part 15: Equipment protection by type of
protection "n"
IEC/IEEE 60079-30-1 -  Explosive atmospheres - EN 60079-30-1 -
Part 30-1: Electrical resistance trace
heating - General and testing
requirements
Bibliography
Add the following notes for the standards indicated:
IEC 60079-14 NOTE Harmonized as EN 60079-14.
IEC 60079-17 NOTE Harmonized as EN 60079-17.
IEC 60079-7 NOTE Harmonized as EN 60079-7.
IEC 60364-1 NOTE Harmonized as HD 60364-1.

IEC/IEEE 60079-30-2 ®
Edition 1.0 2015-09
INTERNATIONAL
STANDARD
colour
inside
Explosive atmospheres –
Part 30-2: Electrical resistance trace heating – Application guide for design,

installation and maintenance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.260.20 ISBN 978-2-8322-2736-7

– 2 – IEC/IEEE 60079-30-2:2015
© IEC/IEEE 2015
CONTENTS
FOREWORD . 6
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 10
4 Application considerations . 10
4.1 General . 10
4.2 Corrosive areas . 11
4.3 Process temperature accuracy . 11
4.3.1 Type I . 11
4.3.2 Type II . 11
4.3.3 Type III . 11
4.4 Installation considerations . 11
5 Thermal insulation . 12
5.1 General . 12
5.2 Selection of insulating material . 12
5.3 Selection of weather barrier (cladding) . 13
5.4 Selection of economical thickness to provide optimum trace heating design. 13
5.5 Double insulation . 14
6 System design . 17
6.1 General . 17
6.2 Purpose of, and major requirement for, trace heating . 17
6.3 Training . 18
6.4 Selection of trace heater . 18
6.4.1 General . 18
6.4.2 Site-fabricated trace heaters . 18
6.4.3 Specific types of trace heating . 19
6.5 Maximum temperature determination . 19
6.5.1 General . 19
6.5.2 PTC characteristic . 19
6.5.3 Stabilized design . 20
6.5.4 Controlled design. 20
6.6 Heat up and cool down considerations . 20
6.7 Design information . 20
6.7.1 Design information documentation . 20
6.7.2 Isometric or trace heater configuration line lists and load charts . 21
6.8 Power system . 22
6.9 Earthing requirements . 22
6.10 Earth-fault protection of equipment . 23
6.11 Start-up at minimum ambient temperatures . 23
6.12 Long trace heater runs . 23
6.13 Flow pattern analysis . 23
6.14 Dead-leg control technique . 25
6.15 Chimney effect . 25
6.16 Safety shower and eyewash station design requirements . 26

IEC/IEEE 60079-30-2:2015 – 3 –
© IEC/IEEE 2015
7 Control and monitoring . 26
7.1 General . 26
7.2 Mechanical controllers . 27
7.3 Electronic controllers . 27
7.4 Application suitability . 27
7.5 Location of controllers . 27
7.6 Location of sensors . 28
7.7 Alarm considerations . 28
7.7.1 General . 28
7.7.2 Trace heating circuit alarm . 28
7.7.3 Temperature alarms . 29
7.7.4 Other alarms . 29
7.7.5 Integrated control . 29
8 Recommendations for installation . 29
8.1 General . 29
8.2 Preparatory work . 30
8.2.1 General . 30
8.2.2 Scheduling and coordination . 30
8.2.3 Confirmation of equipment . 30
8.2.4 Receiving materials . 30
8.2.5 Warehousing and handling . 30
8.2.6 Personnel aspects . 30
8.3 Installation of trace heating circuits . 30
8.3.1 Coordination and equipment verification . 30
8.3.2 Pre-installation testing and design verification . 31
8.3.3 Visual examination . 31
8.3.4 Insulation resistance test . 31
8.3.5 Component substitution . 31
8.3.6 Location of power supply . 31
8.3.7 Installation of trace heaters . 32
8.3.8 Connections and terminations . 34
8.4 Installation of control and monitoring equipment . 36
8.4.1 General . 36
8.4.2 Verification of equipment suitability. 36
8.4.3 Temperature controller and monitoring devices . 36
8.4.4 Sensor considerations . 36
8.4.5 Controller operation, calibration, and access . 40
8.4.6 Necessary modifications . 40
8.5 Installation of thermal insulation system (see also Clause 5) . 40
8.5.1 General . 40
8.5.2 Preparatory work . 40
8.5.3 Installation of the thermal insulation materials . 40
8.5.4 Cladding . 41
8.5.5 Field (site work) circuit insulation resistance test . 41
8.5.6 Visual inspection . 41
8.5.7 Documentation . 42
8.6 Installation of distribution wiring and coordination with branch circuits . 42
8.6.1 General . 42
8.6.2 Earth-fault protective device . 42

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© IEC/IEEE 2015
8.6.3 Circuit protective device . 42
8.6.4 Tagging/Identification . 42
8.7 Commissioning . 42
8.7.1 Pre-commissioning check . 42
8.7.2 Functional check and final documentation. 43
9 Maintenance . 44
9.1 General . 44
9.2 Fault location . 44
9.3 Fault rectification . 44
10 Repairs . 45
10.1 General . 45
10.2 Practicability of repair to electric trace heaters . 45
10.2.1 Mechanical damage . 45
10.2.2 Damage due to corrosion . 45
10.2.3 Damage due to overheating . 45
10.3 Repair techniques for electrical trace heaters . 45
10.3.1 General . 45
10.3.2 In-line splice . 46
10.3.3 Connection via junction box . 46
10.4 Earthing . 46
10.5 Testing . 46
Annex A (informative) Example of design data record . 47
Annex B (informative) Checklist for installation requirements . 48
Annex C (informative) Example of trace heater commissioning record . 50
Annex D (informative) Example of maintenance schedule and log record . 52
Annex E (informative) Pipe heat loss considerations – Heat loss formula and example
calculations . 54
Annex F (informative) Vessel heat loss considerations . 60
F.1 General . 60
F.2 Insulation heat loss (Q ) . 60
ins
F.3 Slab surface areas (Q ) . 61
slab
F.4 Support heat loss (Q ) . 61
supt
F.5 Manhole heat loss (Q ) . 62
manhole
F.6 Convection coefficient formulae . 62
F.6.1 General . 62
F.6.2 Free convection, nonfluid surface, any orientation (h , h , h ) . 62
i co o
F.6.3 Forced convection, any orientation (h ) . 63
F.6.4 Radiation component, all coefficients (h , h , h , h ) . 63
f i co o
Annex G (informative) Heat up and cool down considerations . 65
G.1 Heat up . 65
G.2 Cool down . 66
Annex H (informative) Method to determine equivalent thicknesses of insulating
cements . 68
Bibliography . 69

Figure 1 – Thermal insulation – Weather-barrier installation . 15
Figure 2 – Typical temperature profile . 16

IEC/IEEE 60079-30-2:2015 – 5 –
© IEC/IEEE 2015
Figure 3 – Flow pattern analysis example . 24
Figure 4 – Bypass example . 25
Figure 5 – Typical installation of control sensor and sensor for temperature limiting
control . 38
Figure 6 – Limiting device sensor on sheath of trace heater . 38
Figure 7 – Limiting device sensor as artificial hot spot . 39
Figure E.1 – Assumed temperature gradients . 55

Table 1 – Pre-installation checks . 32
Table A.1 – Example of design data record . 47
Table B.1 – Example of pre-commissioning check and trace heater installation record . 48
Table C.1 – Example of trace heater commissioning record . 50
Table D.1 – Example of maintenance schedule and log record. 52

– 6 – IEC/IEEE 60079-30-2:2015
© IEC/IEEE 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 30-2: Electrical resistance trace heating –
Application guide for design, installation and maintenance

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation.
IEEE Standards documents are developed within IEEE Societies and Standards Coordinating Committees of the
IEEE Standards Association (IEEE-SA) Standards Board. IEEE develops its standards through a consensus
development process, approved by the American National Standards Institute, which brings together volunteers
representing varied viewpoints and interests to achieve the final product. Volunteers are not necessarily
members of IEEE and serve without compensation. While IEEE administers the process and establishes rules
to promote fairness in the consensus development process, IEEE does not independently evaluate, test, or
verify the accuracy of any of the information contained in its standards. Use of IEEE Standards documents is
wholly voluntary. IEEE documents are made available for use subject to important notices and legal disclaimers
(see http://standards.ieee.org/IPR/disclaimers.html for more information).
IEC collaborates closely with IEEE in accordance with conditions determined by agreement between the two
organizations. This Dual Logo International Standard was jointly developed by the IEC and IEEE under the
terms of that agreement.
2) The formal decisions of IEC on technical matters express, as nearly as possible, an international consensus of
opinion on the relevant subjects since each technical committee has representation from all interested IEC
National Committees. The formal decisions of IEEE on technical matters, once consensus within IEEE Societies
and Standards Coordinating Committees has been reached, is determined by a balanced ballot of materially
interested parties who indicate interest in reviewing the proposed standard. Final approval of the IEEE
standards document is given by the IEEE Standards Association (IEEE-SA) Standards Board.
3) IEC/IEEE Publications have the form of recommendations for international use and are accepted by IEC
National Committees/IEEE Societies in that sense. While all reasonable efforts are made to ensure that the
technical content of IEC/IEEE Publications is accurate, IEC or IEEE cannot be held responsible for the way in
which they are used or for any misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
(including IEC/IEEE Publications) transparently to the maximum extent possible in their national and regional
publications. Any divergence between any IEC/IEEE Publication and the corresponding national or regional
publication shall be clearly indicated in the latter.
5) IEC and IEEE do not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC and IEEE are not responsible
for any services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or IEEE or their directors, employees, servants or agents including individual
experts and members of technical committees and IEC National Committees, or volunteers of IEEE Societies
and the Standards Coordinating Committees of the IEEE Standards Association (IEEE-SA) Standards Board,
for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect,
or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this
IEC/IEEE Publication or any other IEC or IEEE Publications.
8) Attention is drawn to the normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that implementation of this IEC/IEEE Publication may require use of
material covered by patent rights. By publication of this standard, no position is taken with respect to the
existence or validity of any patent rights in connection therewith. IEC or IEEE shall not be held responsible for
identifying Essential Patent Claims for which a license may be required, for conducting inquiries into the legal
validity or scope of Patent Claims or determining whether any licensing terms or conditions provided in
connection with submission of a Letter of Assurance, if any, or in any licensing agreements are reasonable or
non-discriminatory. Users of this standard are expressly advised that determination of the validity of any patent
rights, and the risk of infringement of such rights, is entirely their own responsibility.

IEC/IEEE 60079-30-2:2015 – 7 –
© IEC/IEEE 2015
International Standard IEC/IEEE 60079-30-2 has been prepared by IEC technical committee
31: Equipment for explosive atmospheres, in cooperation with the Petroleum & Chemical
Industry Committee of the IEEE Industrial Applications Society under the IEC/IEEE Dual Logo
Agreement.
NOTE A list of IEEE participants can be found at the following URL:
http://standards.ieee.org/downloads/60079/60079-30-2-2015/60079-30-2-2015_wg-participants.pdf.
This first edition of IEC/IEEE 60079-30-2 cancels and replaces the first edition of IEC 60079-
30-2 published in 2007 and constitutes a technical revision.
This edition includes the following significant changes, apart from a general review and
updating of the first edition of IEC 60079-30-2, harmonization with IEEE Std 515, with respect
to the previous edition:
• the relocation of trace heater product design methodology and requirements to IEC/IEEE
60079-30-1;
• the relocation and/or duplication of information on installation, maintenance, and repair to
the MTs under SC31J for their addition into IEC 60079-14, IEC 60079-17, and IEC 60079-
19;
• the inclusion of more detailed information on safety showers and eyewash units;
• the introduction of Annexes from IEEE Std 515.
The significance of changes between IEC 60079-30-2, Edition 1.0 (2007) and IEC/IEEE
60079-30-2, Edition 1.0 (2014) is as listed below:
Type
Changes Clause Minor and Extension Major
editorial technical
changes changes
Addition of clarification for the exclusion of areas
1 X
coverage classifications of EPLs Ga and Da
Addition of requirements for the Division method of
1  C1
area classification that may be applied by some users
Relocation of heat loss design requirements to
6.3 X
IEC/IEEE 60079-30-1
Addition of safety shower and eyewash station design
6.16  C2
requirements
Addition of Annex for an example of a design data
Annex A X
record
Addition of Annex for a checklist of installation
Annex B X
requirements
Addition of Annex for an example of a trace heater
Annex C X
commissioning record
Addition of Annex for an example of a maintenance
Annex D X
schedule and log record
Addition of Annex for pipe heat loss considerations Annex E X
Addition of Annex for vessel heat loss considerations Annex F X
Addition of Annex for heat up and cool down
Annex G X
considerations
Addition of Annex for a method to determine the
Annex H X
equivalent thickness of insulating cements
NOTE The technical changes referred to include the significance of technical changes in the revised IEC
Standard, but they do not form an exhaustive list of all modifications from the previous version.

– 8 – IEC/IEEE 60079-30-2:2015
© IEC/IEEE 2015
Explanations:
A) Definitions
Minor and editorial changes
clarification
decrease of technical requirements
minor technical change
editorial corrections
These are changes which modify requirements in an editorial or a minor technical way. They
include changes of the wording to clarify technical requirements without any technical change,
or a reduction in level of existing requirement.
Extension   addition of technical options
These are changes which add new or modify existing technical requirements, in a way that
new options are given, but without increasing requirements for equipment that was fully
compliant with the previous standard. Therefore, these will not have to be considered for
products in conformity with the preceding edition.
Major technical changes  addition of technical requirements
increase of technical requirements
These are changes to technical requirements (addition, increase of the level or removal)
made in a way that a product in conformity with the preceding edition will not always be able
to fulfil the requirements given in the later edition. These changes have to be considered for
products in conformity with the preceding edition. For these changes additional information is
provided in clause B) below.
NOTE These changes represent current technological knowledge. However, these changes should not normally
have an influence on equipment already placed on the market.
B) Information about the background of ‘Major Technical Changes’
C1 – The requirements for the Division method of area classification are applicable only for
users of this standard intending qualification for these areas.
C2 – The design requirements for safety showers and eyewash units have been included for
harmonization and for added safety.
The text of this standard is based on the following IEC documents:
FDIS Report on voting
31/1190/FDIS 31/1199/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
International standards are drafted in accordance with the ISO/IEC Directives, Part 2.
This standard is intended to be used in conjunction with IEC/IEEE 60079-30-1:2014,
Explosive atmospheres – Part 30-1: Electrical resistance trace heating – General and testing
requirements.
A list of all parts of IEC 60079 series, under the general title Explosive atmospheres, can be
found on the IEC website.
IEC/IEEE 60079-30-2:2015 – 9 –
© IEC/IEEE 2015
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 10 – IEC/IEEE 60079-30-2:2015
© IEC/IEEE 2015
EXPLOSIVE ATMOSPHERES –
Part 30-2: Electrical resistance trace heating –
Application guide for design, installation and maintenance

1 Scope
This part of IEC 60079 provides guidance for the application of electrical resistance trace
heating systems in areas where explosive atmospheres may be present, with the exclusion of
those classified as requiring EPL Ga/Da (traditional relationship to Zone 0 and Zone 20
respectively). This standard also provides guidance for explosive atmospheres incorporating
the Division method of area classification that may be applied by some users of this standard.
NOTE Information on the Division method is given in NFPA 70 and CSA C22.1.
It provides recommendations for the design, installation, maintenance and repair of trace
heating systems including associated control and monitoring equipment. It does not cover
devices that operate by induction heating, skin effect heating or direct pipeline heating, nor
those intended for stress relieving.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-426, International Electrotechnical Vocabulary – Part 426: Equipment for explosive
atmospheres
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
IEC 60079-15, Explosive atmospheres – Part 15: Equipment protection by type of protection
“n”
IEC/IEEE 60079-30-1, Explosive atmospheres – Part 30-1: Electrical resistance trace heating
– General and testing requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-426,
IEC 60079-0 and IEC/IEEE 60079-30-1 apply.
4 Application considerations
4.1 General
This part of IEC 60079 supplements the requirements specified in IEC 60079-14, IEC 60079-
17 and IEC/IEEE 60079-30-1.
Where trace heating systems are to be installed in explosive atmospheres, full details of the
area classifications shall be specified. The specification shall state, as applicable, the

IEC/IEEE 60079-30-2:2015 – 11 –
© IEC/IEEE 2015
required equipment protection levels Gb, Gc, Db, and Dc (traditional relationship to Zone 1,
Zone 2, Zone 21, and Zone 22 respectively), and/or the Division 1 and Division 2 explosive
atmospheres, the gas or dust groups, and temperature classification. Where special
considerations apply or where site conditions may be especially onerous, these conditions
shall be detailed in the trace heating specification.
The specification for heating systems to be installed on mobile equipment or skid units (e.g.
re-locatable structures) should accommodate the adverse conditions in which the trace
heating system may be used.
Where any parts of the trace heating system are likely to be exposed, those parts should be
suitable for the environment.
4.2 Corrosive areas
All components of electric trace heating systems should be examined to verify that they are
compatible with any corrosive materials that may be encountered during the lifetime of the
system. Trace heating systems operating in corrosive environments have a higher potential
for failure than in non-corrosive environments. Deterioration of the thermal insulation system
is made worse by corrosion of the weather barrier and the possibility of moisture leaks
soaking the thermal insulation.
4.3 Process temperature accuracy
4.3.1 Type I
A Type I process is one for which the temperature should be maintained above a minimum
point. Ambient sensing control may be acceptable. Large blocks of power may be controlled
by means of a single control device and an electrical distribution panel board. Heat input may
be provided unnecessarily at times and wide temperature excursions should be tolerable.
Energy efficiency may be improved through the use of dead-leg control or ambient
proportional control techniques (see 6.14).
4.3.2 Type II
A Type II process is one for which the temperature should be maintained within a moderate
band. Control by mechanical thermostats is typical.
4.3.3 Type III
A Type III process is one for which the temperature should be controlled within a narrow
band. Electronic controllers using thermocouple or resistance-temperature detector (RTD)
process temperature sensors facilitate field (work site) calibration and provide maximum
flexibility in the selection of temperature alarm and monitoring functions. Heat input capability
may be provided to preheat an empty pipe or raise the fluid temperature, or both, within a
specified range and time interval. Type III systems require strict adherence to flow patterns
and thermal insulation systems.
4.4 Installation considerations
If failure of any part of the trace heating system can result in a safety or process problem,
then the trace heating system may be considered to be a critical component of the total
process. The temperature control and circuit monitoring requirements of an application may
be defined according to the temperature control types described in 4.3.
When trace heating is critical to the process, circuit monitoring for correct operation,
malfunction alarms, and back-up trace heaters should be considered. Spare or back-up
controllers can be specified to be automatically activated in the event of a fault being
indicated by the monitoring/alarm system. Back-up trace heaters may allow maintenance or
repairs to be performed without a process shutdown and may be used to enhance reliability.

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© IEC/IEEE 2015
5 Thermal insulation
5.1 General
The selection, installation and maintenance of thermal insulation is a key component in the
performance of an electrical trace heating system. The thermal insulation s
...