Can I fit my own components inside a certified empty Ex enclosure?

Not on the strength of the enclosure's certificate alone. An empty Ex enclosure is normally certified as an Ex component (certificate number ending in U), and whoever puts equipment inside it becomes the manufacturer of new Ex equipment, which needs its own conformity assessment: an IECEx certificate under IECEx, and under ATEX a notified-body certificate for category 1 and 2 electrical equipment (category 3 follows internal production control). The only exception is an enclosure certified as equipment whose certificate itself defines what may go inside, for example an increased-safety junction box with a rated set of terminals, and then only within those limits.

Short answer

• Empty flameproof (Ex d) and increased-safety (Ex e) enclosures are usually sold with a U certificate. The certificate says the item is incomplete; it is not an equipment certificate.
• Filling the enclosure is a manufacturing step. The European Commission's ATEX Guidelines state that a user who has to add items such as an enclosure acts as a manufacturer, and that drilling an Ex d enclosure belongs to the manufacturer's assessed production.
• The component certificate makes the equipment certificate easier, not unnecessary. Its schedule of limitations lists what must still be checked: entry holes, free space, temperature class, permitted contents.
• Certified junction boxes can be configured within their rating. IEC 60079-7 gives Ex e junction boxes a rating as either a maximum dissipated power or a defined arrangement of terminals, conductors and currents.
• Anything outside the certificate is a modification that must go back to the manufacturer or a certification route.

Why the contents decide the protection

A flameproof enclosure contains an internal explosion. How high the pressure rises depends on the free volume and on how the contents divide it: components that split the space can cause pressure piling. The heat produced inside sets the surface temperature, and so the temperature class. Every extra hole is a potential flamepath. None of these can be judged from the empty enclosure.

IEC 60079-1 therefore treats an empty flameproof enclosure as an Ex component enclosure and sets rules for it in a normative annex. In the 2014 edition (the version with public text):

• the certificate's schedule of limitations must state the maximum number, size and position of apertures; no other holes may be drilled;
• contents may be placed in any arrangement only if a stated share of each cross-section stays free for unimpeded gas flow: at least 20 % for Groups I, IIA and IIB and at least 40 % for IIC;
• oil-filled circuit-breakers and contactors must not be used;
• the Ex marking string goes inside the enclosure only, never outside, so an empty enclosure cannot be mistaken for finished equipment (it may be omitted where the enclosure maker will itself hold the equipment certificate);
• the equipment certificate is then prepared from documents showing the actual contents and their mounting, normally without repeating the enclosure's own type tests.

IEC 60079-7 applies the same idea to Ex e: an Ex component enclosure carries its marking internally and not externally.

When you may fit contents: certified junction boxes

Increased-safety connection and junction boxes are a special case because their main heat source is the cables and terminals. IEC 60079-7 requires each such box to have a rating expressed as either:

• a rated maximum dissipated power: any number of recognised terminals may be fitted, up to the physical limit, provided the calculated dissipation of terminals and conductors stays within the rating; or
• a defined arrangement: for each terminal size, the permitted number and size of conductors and the maximum current.

If the certificate is an equipment certificate with such a rating, configuring terminals within it is foreseen by the certificate. You still use only the terminal types and accessories the certificate and instructions allow, and you keep the calculation with the installation records.

Common mistakes

• "The enclosure is ATEX certified, so the panel is." A U certificate covers the box, not the panel built in it.
• Drilling an extra entry on site in an Ex d enclosure. Only the holes permitted by the certificate may exist, made under the manufacturer's control.
• Overfilling a flameproof enclosure so that the required free cross-section is lost.
• Fitting ordinary relays, switches or power supplies in an Ex e box. Ex e does not cover sparking parts in normal operation.

Related on excodex

• The X and U suffixes on Ex certificates: specific conditions of use and Ex components
• Flameproof enclosures (Ex d): how flamepaths stop an internal explosion
• What does the U suffix mean, and can a U-certified component be installed on its own?
• Can switches be installed in an Ex e enclosure?
• Can you drill a cable entry in an Ex d enclosure?

Standards and further reading

• IEC 60079-1, flameproof enclosures "d", normative annex on empty flameproof enclosures as Ex components (public copy of the 2014 edition; IEC 60079-1:2026 is current): law.resource.org (PDF)
• IEC 60079-7, increased safety "e", rating of junction boxes and marking of Ex component enclosures (edition 5.1, 2015+AMD1:2017; public copy of 2015): law.resource.org (PDF)
• European Commission, ATEX 2014/34/EU Guidelines, 6th edition (January 2026), sections 47 and 48, including the empty Ex d enclosure example: single-market-economy.ec.europa.eu (PDF)
• US Coast Guard OCS National Center of Expertise, Drill Down 29 on component certificates and schedules of limitations: dco.uscg.mil
• IEC 60079-19, repair, overhaul and reclamation, for changes to equipment already in service.
• Directive 2014/34/EU, Article 13, conformity assessment procedures by category: legislation.gov.uk

This article is general technical information prepared by the excodex editorial team. It does not replace the applicable standards, the equipment certificates and instructions, national regulations or the assessment of a competent person.