Ex Schedule Drawing Requirements

Ex Schedule Drawing Requirements

‘Type Approval’ is achieved by ensuring necessary safety aspects of the product are described the schedule drawings  listed on the certificate that we issue. It is really the ‘drawings’ that are certified, and once issued only products manufactured exactly to the drawings listed in the certificate schedule are covered by the certificate

The certification drawings and other documentation that form the specification of the product are used by the certifying body for comparison with a prototype or sample and in conjunction with an Ex test report to demonstrate conformity with the standard(s).
The drawings and other documentation that forms the specification of the product are a definitive specification of the product that has been certified.
The certificate holder/manufacturer uses the certification drawings and documents to record the controlled details (the elements of the design which provide the protection for the applicable explosion protection technique(s)). It is recommended that manufacturers prepare drawings specifically for the purpose of certification and do not necessarily provide every detail necessary to manufacture the product. The details provided in these drawings may only be modified by reference to the certifying body.
These drawings and documents are also used for audit and/or final inspection purposes.
The certification drawings and documents do not need to provide any information with regard to features not related to conformity with the standard(s). However in such cases the manufacturer must ensure an effective system for controlling manufacturing drawings derived from the certification drawings.
The certification drawings and documents may only be changed after the certifying body in a supplementary certificate gives approval

1     Drawing and Documentation Content

The equipment manufacturer will often require the maximum degree of flexibility to cater for production changes and product variants while the certifying body will require a level of detail which demonstrates that every aspect of the certification process and the relevant standards have been clearly considered and that all details relevant to conformity have been defined unambiguously. The trade off to be achieved relates to the work that the certifying body would need to carry out to ensure conformity over the whole range of the defined flexibility.
The remainder of this document provides guidance regarding the detail required for each standard. It is not sufficient to include statements in drawings and other documentation that forms the specification of the product that simply replicate clauses from the applicable standard, eg ‘All fasteners require the use of a tool’ – the drawing should clearly show or make reference to a specific fastener.
Where typical drawings are used, the drawing must specify what it is typical of. A drawing of an enclosure showing the typical position of a widget does not control the location of the widget unless boundaries of permitted positions are defined.
Where a generalised statement is used in a drawing it must be clear where it applies. For example a general note stating “All gasket material to be 3mm thick neoprene rubber” is only valid if the drawing clearly shows the position of every gasket critical to conformity.
Material specifications on drawings are generally to be taken as material purchasing specifications and should be adequate for that purpose. Any material bought against the specification should perform sufficiently like that used for the prototype sample to give confidence that the test results would be replicated. Where possible, materials should be specified against a standard specification.
Where a material is specified by its performance, the manufacturer must be able to demonstrate how this requirement is met in production. For example material specified “epoxy glass resin with a CTI of greater than 175” would require proof of compliance with the CTI limit for each purchased batch.

2     Specific Requirements

The drawing and documentation requirements for the various explosion protection techniques are as follows:

2.1      General Requirement


All drawings shall be identified by: Drawing Number; Revision Number; Date of Revision; Title; Name of the Design Authority in whose Drawing Record System the drawing is recorded (with relationship to the manufacturer if different).


All measurements given on drawings should be expressed in SI units.


All dimensions relevant to compliance with the standards shall be toleranced unless not required by a specific standard.


A drawing shall show details of labelling, including all details required for compliance with the standards and all specific warning information required by the standards. The label material and method of fixing shall be provided.


Materials of parts relevant to the type of protection shall be unambiguously identified. Where possible, this should be by reference to a material grade given in an IEC Standard.
Where no relevant IEC Standard is available, reference may be made to other local standards, but the applicant should be prepared to submit a copy of the standard if requested.
Where no standard is available, or where the standard does not control all relevant requirements, the material manufacturer’s data sheet shall be submitted.


For plastic materials the following is required:

  • Full definition of the compound manufacturing process
  • Either a full specification of the plastic material or provide description and manufacturer
  • Resistance to light data (if available)
  • Surface resistivity data
  • Temperature index (TI) or relative thermal index (RTI)


For enclosures of light alloys, the percentage content (and tolerance) of aluminium, titanium and magnesium will normally be required.


For earthing and bonding connections, the form of connection, capacity and corrosion protection shall be identified.


For rotating machines, the drawing shall identify all possible points where rotational clearance is relevant, together with information to determine how the minimum clearances required by the standards are achieved on assembly.


For luminaires, details of mounting and guarding (where applicable) to be provided.


Where ingress protection is relevant, materials of gaskets (and ‘O’ rings) and the method of ensuring or controlling compression of the gaskets in service shall be clear. Dimensions of gaskets and related features shall be specified.


Overall nominal dimensions and layout are to be specified.


Details for permanent joints (e.g. welding) are to be specified .


Clamping and sealing arrangement of covers and doors are to be specified.


Circuit diagram (single line) including details of external connections.


If repairable, winding and winding insulation data should be specified.


Ratings of all protection devices are to be specified.


Correctly scaled general arrangement and enclosure drawings

2.2      Flameproof Enclosure d

The following dimensions/details must be shown in the drawings/documents for the apparatus:


Length of flamepath and maximum constructional flamepath gap.


Length, size and minimum yield strength (±0.2%) or grade of fasteners.   Fastener data and characteristics may be included in a table cross referenced to the applicable drawing(s)


Spacing of boltholes in covers.


Size of clearance holes for fasteners.


Depth of drilling and tapping.


Minimum thickness of metal around holes.


Diameter of shafts and bores together with maximum and minimum radial clearances of rotating parts.


Location of threaded entries, range of sizes and maximum number.


Details of threaded entries to include size, pitch, class of fit, length of thread provided in enclosure, dimension of chamfer or undercut.


Area in which fittings, including cable entries, switch operators, windows, receptacles etc to be shown if optional – location of fittings to be specified.


Method of retaining a non threaded fitting e.g. a fitting having a spigot joint.


Hole spacing on face of enclosure where a certified component is to be fitted.


Bearing specification for rotating machines to allow for calculation of ‘m’ and ‘k’.


Metal type and details (including locations) of earthing and bonding facilities


Overall dimensions of the enclosure including minimum wall thickness.


Weld type and size.


Constructional length of flame path ‘L’ & ‘l’.


Minimum thickness of window, material and method of mounting.


Layout and heat dissipation of internal components showing location and approximate dimensions of each component, including clearances between components and the nearest sidewall.  The purpose is to control:

  • Location of sources of heat, for temperature classification purposes, for temperature withstand of plastic parts, window cement, other potting materials, cable entries, etc., and for confirming the local ambient for items such as IS safety barriers
  • Dimensions relevant to pressure piling effects

Where the certificate is to cover variations in content, all versions must to be fully specified.  The ExTL can then select the worst case arrangement(s) for test purposes.


Surface roughness of flamepaths.


Cemented joints require cement to be specified and manufacturers data sheet submitted and the shortest distance through the cemented joint is to be specified.


Washers (if used), washer thickness.


Setting compounds used in stopping boxes etc must be specified and data sheet provided.


Sintered metal components forming part of the enclosure are to be fully specified – material, max bubble pore size, minimum density, dimensions etc.


Comparative Tracking Index (CTI) for insulating material subject to electrical stress if the type of protection depends on it, e.g. through going bushes.


State gross and net internal volumes if not evident from general dimensions.


Declare any cells/batteries and precautions taken.


Details and location of any internal thermal protective devices.


Construction drawings for combustible sensors

  • materials
  • maximum bubble test pore size (m)
  • density
  • minimum thickness

2.3      Increased safety e

The following dimensions/details must be shown in the drawings/documents for the apparatus:


Creepage and clearance distances to be shown.


Comparative Tracking Index (CTI) to be specified on drawings.  A data sheet for the material is also required.


Type and details of terminals used in junction boxes.


Insulation on windings shall be specified by manufacturer’s data sheet.  All relevant processes – e.g. for impregnation, shall also be fully defined.


All insulating materials to be specified on drawings and data sheets supplied where not defined by reference to an IEC standard.


Drawings for motors shall be dimensioned such that it is possible to calculate the minimum and maximum radial air gap unless gap is set during construction. Table of dimensions to take account of all clearances and eccentricities.


Warning label drawings shall be supplied (either separate drawing(s) or included on other relevant drawings) – including material and method of marking and fixing.


If motors are intended for use with soft starters/frequency converters, these devices shall be specified in the drawings.


Details of temperature limiting devices.


Details of associated external protection devices (e.g. certified overload protection device for a motor).


Details of electrical components of luminaires including lamps, lampholders, ballasts, terminals, starting circuits, fuses and batteries.

2.4      Intrinsic safety i

The following dimensions/details must be shown in the drawings/documents for the apparatus:


Components used in a circuit on which the intrinsic safety depends must be specifically marked on the circuit diagram or in the parts list.    It is recommended that these components be identified.  A note explaining any identification symbol should be included in the drawing (eg  “These components are safety components and may not be altered without approval of the Certification Body”).     It is also recommended that the boundary between the parts of the circuit(s) upon which intrinsic safety depends and other parts of the circuit(s) be clearly defined, e.g. by a dotted line.


All safety distances in relation to the tracks on the wiring board must be specified.


All safety distances between components/terminals/within safety components must be specified.


Minimum track width must be specified.


Minimum cross-sectional area, conductor type and insulation thickness of wires must be specified.


The Comparative Tracking Index (CTI) for the wiring board must be specified.


Ratings/tolerances/types of all components on which intrinsic safety depends must be specified.


If transformers are used, the internal insulation system must be specified (distances/insulation class/materials).


If galvanic separation of components is used the internal separation distances must be specified (eg opto couplers) unless addressed otherwise by the standard.


General Arrangement drawings, correctly scaled, marked types.


Block diagram depicting:

  • Which parts of the circuit are in a safe area(s) and which parts are in a hazardous area(s)
  • The connections between assemblies 


Correctly scaled PCB layout drawings including:

  • PCB material and thickness
  • Distance between layers (if applicable)
  • Track material and thickness
  • Electronic copies of the Gerber files


Full schematics/circuit diagrams – component designations to correlate with parts list.


Full parts list including:

  • Nominal values
  • Tolerances
  • Ratings
  • Manufacturer’s part number


Assembly manufacturing drawings for:

  • Transformers
  • Optocouples
  • Relays


Details of application and properties of insulating varnishes (conformal coatings).


Full specification of all equipment in a dedicated system.

2.5      Encapsulation m

The following dimensions/details must be shown in the drawings/documents for the apparatus:


The encapsulation compound(s) shall be specified by the manufacturer’s data sheet. At least the following data shall be available:

  1. name and address of the manufacturer of the compound
  2. precise compound description
  3.  specification of colour / fillers / additives and so on
  4. temperature range
  5. the continuous operating temperature.


The production process of filling the equipment with compound shall be described.  Preferable is a quality system work instruction or manufacturer’s recommended instruction.


A drawing must show the minimum distance from components within the encapsulation to the nearest surface of the compound.


Maximum electrical input parameters must be specified

2.6      Pressurisation p

The following dimensions/details must be shown in the drawings/documents for the apparatus:


Diagram showing the purge and pressurisation “plumbing”, components, pressure gauges etc.


Where relevant a schematic showing the control circuit for purging and pressurisation, normal operation and shut down.  Define settings and limits and provide a statement on safety integrity that is compatible with the level of protection being claimed. NB use of IEC 61508 is a preferred option.


General Arrangement of purged enclosure with dimensions.  Gross free volume to be stated on drawings.  Show material and method of construction.


State purging gas.


State maximum, minimum and normal operating pressure on drawing.


Show intake and outlet ducting and manifold distribution system if applicable.


Show/state details of certified components/equipment.


Detail windows and all other throughgoing devices e.g. pushbuttons, indicator lamps, etc


Show layout of internal components and their thermal dissipation.


Show how venting of any large enclosure volume is achieved.


State presence of any cells/batteries and precautions taken.

2.7      Non-sparking n

The following dimensions/details must be shown in the drawings/documents for the apparatus:


General Arrangement of enclosure giving principle dimensions.


Degree of Protection sealing methods and seal details.


Details of connection facilities and distances for determination of Clearance and Creepage.


Details of connection methods for jointing internal wiring.


All Clearances and Creepages showing actual paths.


Rotating Machines – Rotor bars shall be detailed as to fixing to the rotor and the method of fixing/connection to shorting rings.


Fan clearances or minimum value to be stated .


Details of Variable Voltage Variable Frequency (VVVF) drives and their parameters for the motor to operate within its temperature class are to be supplied.


Details/specification of fuses if applicable.


Plugs and Sockets – General Arrangement showing special facilities (if applicable) to ensure plug and socket cannot vibrate loose.


Luminaires – lampholder, starter and starter holder types to be specified.


Warning labels where applicable.


Enclosed break devices and non-incendive components.  Specify free internal volume of components.


Thermal stability parameters of any poured seals or encapsulating materials.


For sealed or encapsulated devices specify any free volume.


Details of temperature limiting devices.


Details of associated external protection devices (e.g. temperature control on heater).

2.8      Dust Protection by Enclosure tD

The following dimensions/details must be shown in the drawings/documents for the apparatus:


Sealing method/arrangement/shaft seals/bellows.


General Arrangement of enclosure/equipment.


Internal electrical equipment.  General Arrangement Layout.  Power rating.


All gasket sizes, material, thickness, shape etc.


Hole spacing for fasteners.  Specify fastener type.


Joints.  Sizes, type, thread engagement, flange, spigot etc.


Warning labels.


Shows on drawing all holes into enclosure, threaded entries, thread length etc.


Materials of enclosure, window material, thickness, sealing etc.

2.9      Oil-immersion o

The following dimensions/details must be shown in the drawings/documents for the apparatus:


A general arrangement drawing showing enclosure details, bolt/screw hole spacing, enclosure material specification.


Pressure relief device and its release pressure for sealed devices.


Breathing device and drying agent details if enclosure is not sealed. A maintenance specification is required for the drying agent.


Means by which external and internal fasteners are secured from accidental loosening as well as details for securing devices such as liquid level indicators, fill and drain plugs.


Liquid level indicating devices with markings to show the minimum and maximum levels for the protective liquid for the temperature range for which the liquid will be subject to in service.  The level to which electrical equipment shall be filled to be detailed.


Evidence demonstrating that transparent parts will retain their mechanical strength and optical properties when in contact with the protective liquid.


The dipstick and its sealing and guide hole details for non-sealed apparatus. Warning label for replacement of dipstick after use.


Name, description, flashpoint etc of protective liquid.


Immersed live conductive parts and their distances from the surface of the protective liquid.


Method of sealing and securing devices for draining the liquid.


Oil expansion facility for non-sealed enclosures.


Details of means of interrupting the supply in the event that an internal fault produces evolution of gas


Details of electrical terminations and explosion protection technique applied.

2.10    Powder Filling q

The following dimensions/details must be shown in the drawings/documents for the apparatus:


General arrangement showing enclosure details, methods of permanently securing the enclosure (e.g. cementing/rivetting/welding), material specification and thickness.


An exact specification of the filling material and filling process including measures required to ensure proper filling. Manufacturer (name and address) of the filling material to be specified.


Free volume of any electrical devices or components that have a cavity not filled with powder (e.g. relays) to be stated.


Total capacitance with tolerance(s) of all capacitors.


Cable entry and/or bushing sealing.


Sealing to achieve degree of protection.


Maximum width of gap.


PCB trackwork and component layouts (scaled), PCB coatings, component list with component values and tolerances, minimum distance through filling compound between electrically conductive materials and (i) insulated components and (ii) inner surface of enclosure


Fuse current rating In


Thermal protection device
Based on IECEx Operational document No Ex/OD017
Specific additional requirements for Intrinsic Safety can be found here