Can conduit be used instead of cable glands under IEC 60079-14?
Abstract
Yes. IEC 60079-14 includes conduit systems as a wiring method, with rules for selection, installation and flameproof sealing devices. The enclosure must be certified for conduit entry, seals and fittings must be suitable, and the conduit becomes part of the protection.
Yes. IEC 60079-14 recognises conduit systems as a wiring method alongside cables with cable glands, and it has its own clauses on selecting conduits, installing conduit systems and fitting flameproof sealing devices for conduit. Conduit is common in North America and on some plants built to American practice, but much less common in IEC and ATEX installations, where sheathed or armoured cable with certified glands is the norm. When conduit is used, the enclosure must be certified for a conduit entry and the conduit, its fittings and its seals become part of the explosion protection.
Short answer
- Allowed: IEC 60079-14 covers conduit systems for gas (Group II) and dust (Group III) installations, including sealing devices for conduit at flameproof enclosures.
- The enclosure decides first: its certificate and instructions must allow conduit entry (often called direct entry for flameproof enclosures) and state the thread and any sealing requirement.
- Sealing fittings (stopping boxes) are needed to stop flame, pressure piling and gas migration along the conduit: at the entry to flameproof enclosures and where the conduit leaves the hazardous area, as the standard and the certificate require.
- The conduit must be suitable: threaded heavy-gauge metal conduit and certified fittings for flameproof systems, drainage where condensation can collect, and bonding into the equipotential bonding system.
- NEC rules are not IEC rules. The familiar 18 in. and 10 ft seal distances come from NEC section 501.15 for Class I divisions (2023 text; the 2026 edition of NFPA 70 is now current, so check the edition adopted locally); IEC installations follow IEC 60079-14 and the equipment documentation.
Why conduit needs more care than a cable gland
A cable gland closes the entry right at the enclosure wall. A conduit is an open pipe that connects the enclosure with everything else on the run: other enclosures, pull boxes, and possibly the non-hazardous area. Without seals it can carry:
- flame from an internal explosion in a flameproof enclosure to the next enclosure;
- pressure piling, where gas pushed ahead of the flame pre-compresses the mixture elsewhere and makes the next explosion more violent;
- gas or vapour from the hazardous area into a control room or substation;
- water from condensation, which runs down to the lowest enclosure.
This is why IEC 60079-14 treats a conduit system with flameproof equipment as part of the flameproof installation, with sealing devices, rather than as a simple cable support.
How a conduit installation to IEC 60079-14 is put together
- Select equipment certified for conduit entry. Many IEC flameproof enclosures are certified for indirect entry through an Ex e terminal box with glands; direct conduit entry into the flameproof compartment needs the certificate to allow it.
- Fit sealing devices where required. At a flameproof enclosure the 2007 edition asks for the seal to be part of the enclosure or fitted immediately or as close as practicable to the entry, with as few fittings as possible, and the seal must be one the equipment documentation specifies or that complies with IEC 60079-1. Pour the compound after the conductors are pulled. A seal without compound is no seal.
- Seal at boundaries so that gas cannot pass along the conduit from the hazardous area to a non-hazardous one; the 2007 edition allows no union, coupling or other fitting between that seal and the boundary.
- Make threaded joints tight with the thread engagement the system requires, and use only certified fittings and adapters within the limits of the standard.
- Drain low points where water can collect, with drain fittings suitable for the type of protection.
- Bond the conduit. Metal conduit that carries the circuit conductors is an exposed conductive part and must be included in the equipotential bonding.
- Choose suitable conductors. IEC 60079-14 accepts non-sheathed insulated cables in conduit, with a fill limit in the 2007 edition (cables at most 40 % of the conduit cross-section when there are three or more), and the 2024 edition has a clause on single insulated wires; check its conditions.
IEC and NEC side by side
| Topic | NEC Article 501, 2023 text (Class I divisions) | IEC 60079-14 |
|---|---|---|
| Usual wiring method | Threaded rigid metal conduit, Type MI or MC-HL cable (Division 1) | Cables with certified glands; conduit permitted |
| Seal at enclosure with arcing or hot parts | Within 18 in. of the enclosure | Sealing device as the standard and certificate require |
| Seal at boundary | Within 10 ft of the boundary | Sealing so that gas cannot pass between areas |
| Entry threads | NPT | Metric or NPT, as marked on the enclosure |
For North American Zone installations (NEC Article 505) and Canadian practice, the seal rules differ again; see When are conduit sealing fittings required in Ex d installations?.
Example: A skid built in the United States with conduit and explosionproof fittings is installed on a European plant with ATEX zones. The receiving engineer checks that every item on the skid conforms to the ATEX Directive 2014/34/EU for the zone (CE marking, EU declaration of conformity and, where the category requires it, an EU-type examination certificate), that conduit entries and seals match those certificates, that seals are filled, and that the conduit is bonded. Neither a North American listing nor an IECEx certificate alone allows equipment to be placed on the EU market, so items without ATEX conformity are replaced or put through the ATEX procedure.
Common mistakes
- Running conduit into an enclosure certified only for gland entry.
- Unfilled seals or seals placed too far from the enclosure.
- Mixing NPT and metric threads without certified adapters.
- Forgetting drains, so water collects in the lowest enclosure.
Related on excodex
- Ex installation basics under IEC 60079-14
- Zones vs Divisions: IEC and ATEX zones compared with NEC Class I Division 1 and 2
- When are conduit sealing fittings required in Ex d installations?
- What is pressure piling in a flameproof enclosure?
- Standards spaces: IEC 60079-14, NEC 500 to 506
Standards and further reading
- IEC 60079-14, design, selection and installation (edition 6, 2024), clauses on conduits, conduit systems and flameproof sealing devices for conduit: preview
- IEC 60079-14:2007 (edition 4), quoted where the text names that edition; public text as AS/NZS 60079.14:2009
- IEC 60079-1, flameproof enclosures "d" (entries and threaded joints)
- NFPA 70, National Electrical Code, section 501.15 sealing and drainage; NFPA summary of NEC 2023 conduit sealing requirements in Class I locations: nfpa.org resource PDF
- IAEI Magazine, wiring requirements in Class I Division 1 locations (2017): iaeimagazine.org
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.