Can switches or relays be installed inside an Ex e enclosure?
Abstract
Not as ordinary sparking contacts. Ex e allows no arcs or sparks in normal operation, so a switch or relay inside needs its own protection, usually a flameproof contact block (Ex db eb), and the assembly must be covered by an equipment certificate.
Not as ordinary open contacts. Increased safety (Ex e) protects equipment that does not produce arcs or sparks in normal operation, and a switch or relay sparks every time it operates. A switching device can sit inside an Ex e enclosure only if the switching element has its own type of protection, typically a flameproof contact block, or switches only an intrinsically safe circuit, and the finished assembly is covered by an equipment certificate, which gives markings such as Ex db eb.
Short answer
- A standard industrial switch, relay, contactor or circuit breaker must not be fitted in an Ex e enclosure. Its contacts are an ignition source in normal operation.
- For level eb (Zone 1, EPL Gb) the switching element needs another type of protection suitable for EPL Gb: most often a flameproof (
db) contact block or switch chamber, sometimes encapsulation (mb). IEC 60079-7 also excludes semiconductors and electrolytic capacitors from level eb, so solid-state relays are not an Ex e way round the problem. - For level ec (Zone 2 only, EPL Gc) sparking parts can be protected by the Zone 2 methods of IEC 60079-15, such as hermetically sealed or sealed devices and non-incendive components, or by an enclosed-break device (now
dcin IEC 60079-1). - A switch in an intrinsically safe circuit is a different case: the circuit cannot ignite the gas, so the switch is simple apparatus. The IS wiring must then be kept separate from the Ex e circuits.
- In every case the combination must fall within an equipment certificate. Component (
U) certificates for the enclosure and the contact blocks do not certify the finished station.
Why increased safety cannot contain sparking contacts
IEC 60079-7 defines increased safety as additional measures that give increased security against excessive temperatures and against arcs and sparks. The concept has no way of containing an ignition: there is no flamepath, no pressurisation and no energy limit. It works only because nothing inside it ignites the gas in the first place. Good terminals, generous creepage and clearance distances, an IP-rated enclosure and controlled temperatures keep it that way.
A switching contact defeats this. Breaking an inductive load such as a solenoid or contactor coil draws an arc, and even a small control current can produce an incendive spark in a IIC atmosphere. The Ex e enclosure itself is not gas-tight; gas enters it slowly, so the contacts have to be safe in the gas.
How switching is made acceptable
| Protection of the switching element | Typical use | Resulting marking (example) | Zones |
|---|---|---|---|
Flameproof contact block or switch chamber (db) | Push buttons, selector switches, isolators, plug and socket switching | Ex db eb IIC T6 Gb | 1 and 2 |
Encapsulation (mb) of a small relay or switch | Relays and reed contacts in encapsulated modules | Ex eb mb IIC T4 Gb | 1 and 2 |
Enclosed-break device (dc), hermetically sealed or sealed device, non-incendive component (nC) | Relays and switches inside Zone 2 equipment | Ex ec nC IIC T4 Gc | 2 only |
| Intrinsically safe circuit | Contacts switching an IS signal | Ex eb ib or simple apparatus in an IS loop | Per IS level |
For encapsulation, IEC 60079-18 requires switching contacts to have an additional internal enclosure, so that the compound cannot get into the contacts. Level ma also limits the contact rating and requires a hermetically sealed inner enclosure, and at higher switched currents the inner enclosure must be of inorganic material. For Zone 2 equipment, IEC 60079-15 notes that the temperature to be considered is often the outside surface of the nC components inside the ec equipment.
The most common product is the local control station: an Ex e enclosure with Ex e terminals, carrying flameproof contact blocks behind the push buttons and Ex e or Ex d indicator lamps. The flameproof block contains any ignition at its contacts, and the Ex e housing and terminals deal with the wiring.
Who may fit the switch: the certificate question
Panel builders often hold certified empty Ex e enclosures, certified terminals and certified flameproof contact blocks, each with a component certificate number ending in U. Putting them together creates a new product. It is acceptable only when:
- the arrangement falls within an existing equipment certificate that lists the permitted components, quantities, positions and power dissipation (many control station and enclosure certificates do this), and the work is done under the manufacturer's quality system; or
- the assembly is certified in its own right.
Even when every part is certified, adding a relay changes the heat inside the box. Ex e enclosures have a rated maximum dissipated power or a defined terminal and conductor arrangement for their temperature class, and the coil of a relay or the lamp of an indicator counts towards it.
Example: A designer wants a Zone 1 local control station with start and stop buttons, a running lamp and an interposing relay. A certified control station range covers the buttons (flameproof contact blocks) and an LED indicator, but not a relay. The relay is moved to the motor control centre in the safe area, which is also easier to maintain. Fitting it in the field box would have needed a certified encapsulated or flameproof relay module and a certificate covering it.
Common mistakes
- Fitting a "small" 24 V relay in an Ex e junction box. Low voltage does not make a sparking contact safe; it needs its own type of protection and certificate coverage.
- Assuming component certificates make the assembly certified.
Ucertificates are building blocks with a schedule of limitations, not permission to install. - Using Zone 2 switching methods in Zone 1.
nCand enclosed-breakdcdevices are EPL Gc; the station becomesecand Zone 2 only. - Mixing IS and non-IS wiring carelessly. A switch in an IS circuit inside an Ex e box still needs the IS terminals and wiring kept separate from the other circuits.
Related on excodex
- Increased safety (Ex e): preventing sparks, arcs and hot spots
- Combined protection concepts: Ex db eb, Ex d e terminal boxes and multiple markings
- Can you add extra terminals or conductors to an Ex e junction box?
- Can Ex i circuits be terminated inside an Ex e or Ex d enclosure?
- Tools: Ex marking check, standards spaces IEC 60079-7 and IEC 60079-15
Standards and further reading
- IEC 60079-7, equipment protection by increased safety "e" (edition 5.1, 2015 with amendment 1 of 2017), levels eb and ec.
- IEC 60079-1, flameproof enclosures "d", including enclosed-break devices (level dc).
- IEC 60079-15, type of protection "n" (2017), including hermetically sealed, sealed and non-incendive components.
- IEC 60079-18, encapsulation "m" (edition 5, 2025), including the rules for switching contacts.
- IEC 60079-7:2015 text (scope, level eb excluding semiconductors and electrolytic capacitors), incorporated by reference in US federal regulations: law.resource.org
- IEC 60079-15:2017 text (methods for sparking parts at EPL Gc): law.resource.org
- IEC 60079-18:2014+AMD1:2017 text (switching contacts in encapsulated equipment; superseded by the 2025 edition): law.resource.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.