Can you drill an extra cable entry hole in an Ex d enclosure on site?
Abstract
No. An installer must not drill or tap a new entry in a flameproof (Ex d) enclosure. Extra entries are allowed only where the certificate drawings permit them, machined by the manufacturer or by a repair facility working to those drawings under IEC 60079-19.
No. An installer must not drill, punch or tap a new cable entry in a flameproof (Ex d) enclosure on site. An extra entry is acceptable only if the certificate documents allow an entry of that size in that position, and only if it is machined by the manufacturer or by a competent repair facility working to the manufacturer's drawings under IEC 60079-19. Any other hole is a modification, and the enclosure is no longer certified.
Short answer
- IEC 60079-14 states that additional holes shall not be made into flameproof enclosures (wording of the 2007 edition, clause 10.4.1; check the edition you work to).
- The manufacturer's documents state where entries may be fitted and the maximum number of entries (IEC 60079-1). An entry that is not on those documents is not covered by the certificate.
- IEC 60079-19 treats drilling into a flameproof enclosure as a modification. The 2006 edition allowed it only with reference to the manufacturer's certified drawings or, in exceptional cases such as a manufacturer that no longer trades, the certifying authority. Since the 2010 edition, the repair standard permits alterations only where the certification documents specify them, and does not permit modifications.
- The entry thread is itself a flamepath. It needs the right thread form (metric or NPT only for IEC 60079-1:2014 enclosures), a tight tolerance and enough length to give at least five full threads of engagement.
- If you need another cable, first look for a spare entry that is already certified, or a second enclosure. Do not open up the existing box.
Why a drilled hole is not just a hole
A flameproof enclosure works because every opening to the outside is a flamepath that cools escaping gases below the point where they can ignite the atmosphere outside. A threaded cable entry is one of those flamepaths. IEC 60079-1:2014 requires internal metric entry threads of tolerance class 6H or better, with any chamfer or undercut no deeper than 2 mm from the outside wall. Glands and plugs are made with at least eight full threads so that at least five are engaged when fitted.
A hand drill and a tap on a ladder cannot guarantee that. The hole may be off-axis, oversize, or cut with a worn tap. The thread may be too short where the wall is thin. Swarf can fall inside onto live parts or into joint faces. A new hole can also cut into ribs, flanges or internal mounting points. And the wall around it has been pressure-tested only in the configuration that was certified: the type test and routine overpressure test do not cover a hole the manufacturer never made.
There is also a design question that only the manufacturer can answer. The number and position of entries affect the strength of the wall and, through the glands that protrude inside, the internal layout that the explosion tests were made with. That is why IEC 60079-1 requires the manufacturer to state the permitted places and the maximum number of entries in the equipment documents.
Who may add an entry, and how
| Situation | Status | Who does it |
|---|---|---|
| Entry already machined and closed with a certified stopping plug | Normal installation | Installer uses it with a certified gland of the correct thread |
| Extra entry shown as optional on the certificate drawings (size, position, thread) | Alteration within the certificate | Manufacturer, or a repair facility working to those drawings |
| Entry not shown on the drawings | Modification | Not a repair job: only the manufacturer can have the certification extended |
| Hole drilled by the installer | Unauthorised modification | Not acceptable; the equipment must not be used in the hazardous area |
The work is recorded, and the repair facility marks the equipment as described in IEC 60079-19. Where a proposed change would take the equipment outside its certification, IEC 60079-19 requires the user to be told in writing that the equipment is no longer suitable for an explosive atmosphere. An enclosure already drilled without authority is in the same position: it is replaced, or returned to the manufacturer for assessment.
Example: A maintenance team needs one more instrument cable into an Ex db IIB T4 Gb junction box whose four entries are all in use. The certificate drawing shows six possible entry positions. The box is removed, sent to the manufacturer's service centre, and the fifth entry is machined to the drawing with the correct M20 thread and gauged. The box returns with a record of the work. Had the drawing shown only four positions, the right answer would have been a second junction box.
Ex d is not the same as Ex e or Ex t
Increased safety (Ex e) and dust (Ex t) enclosures depend on the degree of ingress protection, not on flamepaths. Some of their certificates and instructions let the user cut plain entry holes within stated limits, such as the hole size tolerance and the spacing between entries. IEC 60079-19 also accepts changes to Ex e entries if the type of protection and the IP rating are kept. Those allowances do not transfer to a flameproof enclosure. Check the instructions for the exact enclosure, and never assume that a rule for one concept applies to another.
Common mistakes
- Drilling and tapping on site because "it is the same thread size". The certificate covers the hole, not only the gland.
- Using a thread adapter to fit a gland into an entry of the wrong thread that was drilled or re-tapped locally. A certified adapter does not legalise an uncertified hole.
- Re-tapping a damaged entry thread with a hand tap. Thread repair is a repair under IEC 60079-19 and belongs in a workshop working to the drawings.
- Leaving swarf inside the enclosure or on the joint faces after any work near the box.
Related on excodex
- Flameproof enclosures (Ex d): how flamepaths stop an internal explosion
- Repair, overhaul and modification of Ex equipment (IEC 60079-19)
- Cable glands for hazardous areas: barrier glands, compound glands and selection
- Can thread adaptors or reducers be used on an Ex d cable entry?
- Standards spaces: IEC 60079-1, IEC 60079-19
Standards and further reading
- IEC 60079-1:2014 (edition 7) with interpretation sheet 1 (2020), flameproof enclosures "d": entry thread requirements, permitted entry places and maximum number of entries; publicly available as incorporated by reference: law.resource.org. A 2026 edition of IEC 60079-1 has since been published.
- IEC 60079-14, design, selection and erection of electrical installations; the 2007 text, published as AS/NZS 60079.14:2009, states in clause 10.4.1 that additional holes shall not be made into flameproof enclosures: archive.org
- P. Thurnherr (convenor of IEC maintenance team MT 60079-14), presentations on IEC 60079-14 including the rule that installers shall not make additional holes in an Ex d enclosure, IECEx conferences in Shanghai (2017) and Split (2018): IECEx 2017, IECEx 2018
- IEC 60079-19, equipment repair, overhaul and reclamation (current edition 5.0, 2025); the 2006 edition, adopted in India as IS/IEC 60079-19, contains the clauses on drilling and additional entries quoted above in paraphrase: law.resource.org
- Polish standards body interpretation of EN 60079-14 clause 10.6.1 (five full threads, sealing washers, grease on parallel threads): pkn.pl
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.