To ‘eb’ or not to ‘eb’, that is the question
01 September 2015
SGS Baseefa General Manager Ron Sinclair MBE is chairman of BSI Committee EXL/31 and the IEC's Cenelec TC31 committee. Here he looks at some of the consequences arising from the publication of IEC 60079-7 Edition 5 in June and the subsequent publication of the EN version, including the change in marking requirements.
With the publication of IEC 60079-7 Edition 5 in June (and the subsequent publication of the EN version), we have seen the largest transfer of technical requirements between Ex standards since the decision to integrate the general requirements for both gas and dust atmospheres in a single standard, IEC 60079-0. So why did we do it, and how has it been achieved?
Historically, with the notable exception of intrinsic safety, all Ex Protection Concepts had a single level of protection, and the installation standard (IEC 60079-14) gave an indication of which hazardous area zones each concept could be used in.
We had just a single protection concept, Ex n, which alone was suitable for installation only in Zone 2. The origins of the requirements given for Ex n in IEC 60079-15 came from a number of disparate sources (many of them older UK standards such as BS 5000-16 for motors and BS 4533-50 for luminaires) and did not always sit well together.
Just over ten years ago, the IEC TC31 standards committee decided that the ATEX Directive had one significant positive advantage over the way that the 60079 series of standards marked the protection concepts. The ATEX Categories (1, 2 or 3) gave a unique overall indication of the level of protection provided by equipment which was, by then, more and more likely to involve a combination of protection types from different standards. The result was the definition of a unique Equipment Protection Level (EPL) that could be allocated to each item of equipment. This was particularly valuable for equipment mounted through vessel walls, where the single item of equipment was mounted in two zones.
Once the EPL system was in place, the logical development was to create different levels of protection in standards other than just 60079-11 for Ex i. Ex ma, mb and mc followed quickly and then the requirements for Ex nL (energy limitation) were moved from 60079-15 to create Ex ic. 60079-31, Dust Protection by Enclosure, which had three levels of protection ‘ta’, ‘tb’ and ‘tc’, from its first edition.
Since the bulk of 60079-15 concerned equipment which did not spark or have a hot surface in normal operation (Ex nA), the logical step was to call this Ex ec and move the requirements into 60079-7. The decision to pursue this path was taken four years ago and the maintenance team (MT) for 60079-7 have been wrestling with this since then.
Once ‘ec’ is in position, equipment previously marked Ex e becomes ‘eb’.
The first problem that hit the MT was that a few requirements for Ex nA were more severe than the equivalent requirements for Ex e. A typical example is where 60079-15 addressed issues related to bearing seals that were not addressed in 60079-7. Other requirements, which were similar, were expressed in different ways. Therefore what was originally envisaged to be a simple exercise turned out to be more complicated and required additional time. However, the principle adopted for the exercise was to make the minimum changes to the requirements for either Ex e or Ex nA in order to ensure a minimum level of disruption for the manufacturer, but still produce a document that was technically consistent for the new levels of protection: Ex eb and Ex ec.
Although this was far from a full technical review, it became necessary to make a few changes for consistency and, additionally, some updates related to “technological knowledge” (the phrase used inthe ATEX Directive) were introduced at the same time.
Clearly the one change that affects all equipment is the change in marking:
• A straightforward motor might change from Ex nA IIC T3 to Ex ec IIC T3 Gc
• A straightforward plastic junction box might change from Ex e IIB T6 to Ex eb IIB T6 Gb
If you want to see a list of every technical change, it can be downloaded free as part of the IEC 60079-7 preview file from the IEC Webstore. But possibly the most important changes are:
• Terminal block insulation pre-conditioning now applies to all terminals, not just rail- mounted types (for ‘eb’ only)
• Testing of ballasts for discharge lamps now includes the lamp failure condition (for ‘eb’and ‘ec’). This particularly picks up the situation where the ballast is protected ‘eb’ but the lamp is protected ‘db’
• It is now prohibited to mark empty component enclosures on the outside with the Ex ‘marking string’ (for ‘eb’ and ‘ec’). This aligns with the latest requirements for empty flameproof enclosures and was introduced to try to prevent the misunderstanding that the component marking allowed direct installation.
• Although not listed as a change (because it is a clarification of the existing requirement), it is now absolutely clear that Ex eb cannot be used as a protection concept for LED light sources, whereas Ex ec may be used.