Ex ob vs Ex oc at a glance
IEC 60079-6:2015+AMD1:2020 CSV is the current consolidated IEC publication checked for this guide. It is Edition 4.1, published on February 24, 2020, with a stability date of 2028.
| Marking element | Level stated by Part 6 | EPL stated in the public scope | Public voltage-scope ceiling | Safe procurement conclusion |
|---|---|---|---|---|
| Ex ob | Level of Protection ob |
Mb or Gb | Rated voltage not exceeding 11 kV RMS AC or DC | Confirm the complete marking and exact certified rating; do not use 11 kV as an assumed product rating |
| Ex oc | Level of Protection oc |
Gc | Rated voltage not exceeding 15 kV RMS AC or DC | Confirm the complete marking and exact certified rating; do not use 15 kV as an assumed product rating |
The table reports only the public scope of IEC 60079-6. It does not assign a Zone, gas group, temperature class, ambient range, electrical rating or certificate status to an offered item.
What liquid immersion o means in this guide
IEC 60079-6 specifies requirements for the design, construction, testing and marking of Ex Equipment and Ex Components using liquid immersion o. Its public scope is for explosive gas atmospheres. The standard supplements and modifies the general requirements in IEC 60079-0:2026. The Part 6 requirement takes precedence where it conflicts with a Part 0 requirement within the Part 6 scope.
Edition 4 replaced the older oil-immersion framing with liquid immersion and introduced the ob and oc levels. This explains older terminology that may still appear in indexes or legacy documents.
The suffix does not disclose the protective liquid, fill level, construction, maintenance method or inspection interval. Those details require the current licensed standard, assessed product documentation and controlled instructions.
Why the EPL mapping must stay attached to the full marking
Part 6 associates ob with EPL Mb or Gb and oc with EPL Gc. The suffix carries protection-level information, but it is not a complete application decision. The full marking must identify the offered item and its applicable fields.
Use the MMAIATEX guide to Equipment Protection Levels when an EPL term needs definition. Then return to the offered item's own marking and certificate. Do not copy an EPL from a comparison guide into a missing nameplate field.
Likewise, use the guide on how to read Ex markings to follow the complete marking chain. Ex ob or Ex oc cannot by itself establish gas group, temperature class, ambient limits, ingress protection, electrical duty or permission for a particular hazardous area.
The 11 kV and 15 kV figures are scope limits
The voltage figures on the IEC page define the upper boundaries within which the respective parts of the standard apply. They do not state that a particular ob item is rated 11 kV or that a particular oc item is rated 15 kV. They also do not prove insulation coordination, circuit duty, temperature behavior or suitability for a supply system.
A lower operating voltage does not make ob and oc interchangeable. The protection level, equipment identity, certified ratings and installation conditions still have to match.
Gas scope does not establish dust suitability
The public IEC 60079-6 scope used for this article is explicit about explosive gas atmospheres. It does not provide a basis for claiming combustible-dust suitability from Ex ob, Ex oc or liquid immersion alone.
If a project includes a dust hazard, select equipment with the complete applicable dust marking and evidence. The MMAIATEX guide to Zone 20, Zone 21 and Zone 22 explains that separate classification question. It cannot convert a gas-only marking into a dust approval.
Read the certificate and product identity together
The IECEx recognized standards page lists IEC 60079-6 among example standards used by the equipment scheme. The listing does not certify a product or replace its certificate record.
For every offered configuration, connect the following fields without filling gaps by assumption:
- Legal manufacturer name and exact product or component identity
- Model, suffix, variant and option codes
- Complete Ex marking, including
oborocin its real context - EPL, gas group and temperature information stated for the item
- Certified ambient range and actual electrical ratings
- Certificate number, issue, current status, scope and schedules
- Conditions or component limitations attached to that evidence
- Controlled installation, operation and maintenance instructions
The MMAIATEX guide on verifying IECEx certificates and ATEX documents provides a broader identity and document check. For this decision, the narrow question remains whether the exact ob or oc configuration and all connected evidence match the real application.
Component and assembly boundaries
IEC 60079-6 covers Ex Equipment and Ex Components, but those are different evidence categories. A component does not establish conformity of finished equipment. Its interfaces, limitations and incorporation conditions must be resolved in the completed design.
The complete assembly evidence must account for every relevant interface. A representative photograph, category label or unchanged suffix cannot prove that a substituted component or revised assembly remains within the assessed construction.
Procurement evidence checklist
Before approving an item marked Ex ob or Ex oc, request and cross-check:
- Exact manufacturer, model, suffix, variant and offered configuration
- Legible complete marking or controlled nameplate artwork
- Current certificate and all schedules for the exact identity
- Stated EPL, gas group, temperature data and certified ambient range
- Actual voltage, current, frequency and other applicable electrical ratings
- Conditions, component limitations and incorporation requirements
- Controlled installation, operation and maintenance instructions
- Drawings or interface documents needed for the completed assembly
- Destination-market declarations and other required conformity documents
- Written confirmation that any substitution or option remains within the approved evidence
Reject a comparison that provides only a protection suffix and a marketing description. The evidence chain must remain traceable from the offered item to the intended site conditions.
A practical decision sequence
First, the responsible designer defines the atmosphere, area classification, required EPL, gas group, temperature limits, ambient range and electrical duty. Procurement records the complete marking and exact identity. Compliance reviewers check the current certificate, scope, schedules, conditions and instructions. Competent parties then verify the real configuration and interfaces.
This sequence keeps Ex ob vs Ex oc in its proper role: it helps interpret one part of the marking, but it does not replace hazardous-area classification, product selection, certificate validation or installation approval.
Current MMAIATEX certification status
The public MMAIATEX About page states that ATEX, IECEx and CCC certification work is in progress. MMAIATEX Explosion-proof Technology (Zhejiang) Co., Ltd. does not present this article, a standard reference, a liquid-immersion suffix, an IP rating, a product category or a representative photograph as proof that a particular product, component or assembly is certified.
Buyers must verify the exact legal manufacturer, model and suffix, complete marking, current certificate status and scope, schedules, declarations where applicable, controlled instructions, destination-market requirements and site conditions before selection or use.
Safety and legal disclaimer
This article provides general technical and procurement education. It does not classify a hazardous area, select an EPL, approve a protective liquid, define construction or maintenance rules, certify a product or assembly, or approve an installation. Competent parties must use the current licensed standards, exact certificate and schedules, manufacturer instructions, site safety procedures and applicable law.
Request an Ex ob or Ex oc evidence review
Send the area classification, required EPL, gas group, temperature and ambient limits, electrical duty, proposed complete marking, exact model, certificate and schedules, assembly information and destination market. MMAIATEX can identify available product information for review by the responsible designer, installer and compliance team.