Basic difference between Zone-2 and Zone-1 equipment

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Nick Thompson

if i have ex d junction boxes can i use blu points to join cables inside? the enclosures have compound filled glands
 
Dear Bruce,

I've been reading your responses to questions regarding haz area applications and thought perhaps you could help me out.

I am using field instruments connected through barriers located at safe area. The haz area falls in Zone 2, gr.IIA/IIB. Please let me know whether I can use a Ex ia instrument in place of Exd ia instrument which will be working on 24vdc through barrier.

Also please let me know why a Exd instrument can NOT be used in zone 0. Or a Exd with ia can work in zone 0. I have lot many other questions in mins and if you don`t mind can I have your email id?

Request to reply me on [email protected]
Thanks in advance.
Sandeep Datar
India.
 
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Hi Sandeep,

An Ex d ia classification sounds as if it belongs to equipment with a high-power drive or supply circuit, and a low-power signal circuit. If you give me more details including an equipment model number or similar I can give a more specific answer.

Assuming it is something like the above, then you will not generally be able to supply enough power through a barrier to the high-power circuit. Even if you could, it is not permitted to connect any equipment that is not certified as IS on the field side of the barrier. This is because equipment designed to meet Ex i requirements has very limited capability to store energy in internal inductance and capacitance - a low-voltage solenoid, for example, may have sufficient inductance to develop an incendive spark if the circuit is broken and would not meet these requirements.

You should be able to get detailed installation specifications from the manufacturer's instruction manual, which should be available to you as it is a necessary part of the Flammable Atmospheres dossier for the installation.

The difference between the zones where different methods of protection can be used is generally based on the integrity of the method - what is the likelihood of the protection being made ineffective because of something like inadequate maintenance or an operating error? This is made clearer in the recent changes to the IEC standards referring to Equipment Protection Levels. In Zone 0 or the dust equivalent of Zone 20, the equipment is exposed to the flammable atmosphere most of the time and must remain safe with at least 2 independent faults. In Zone 1, there is a lower probability that the atmosphere will be flammable and it is adequate for the equipment to remain safe with 1 fault, while for Zone 2 it is acceptable for equipment to be safe in normal operation only and not necessarily if it is faulty (it is expected that the fault will be found and corrected before the equipment is exposed to a flammable atmosphere).

Hope this helps,
Bruce.
 
B
Hi Sandeep,

I've had a look at the installation details given in the operating
instructions

http://www.vega.com/downloads/BA/41824-EN.PDF

and can see why you have a problem! - they are not very clear. I have also checked with the equipment certification from

http://www.vega.com/downloads/ZU/EN/42803-EN.PDF

My interpretation is that this is a simple 2-wire connection not requiring a separate external power supply.

The Ex d ia unit is divided into two sections - components located outside the process vessel, and those exposed to the atmosphere inside the vessel.

The Ex d element is used to provide explosion protection for the terminal chamber, and is rated as safe for the external atmosphere where the sensor is installed. External wiring must meet Ex d rules rather than Ex i. This part of the system has Equipment Protection Level EPL Gb - good for Zone 1.

The Ex ia rating applies to the probe and means that the probe can be inserted into a tank or silo where the atmosphere is Zone 0 (EPL Ga)

With the Ex ia unit, there is no separation between the two components. This unit will need a barrier on the external wiring.

Note that this is my interpretation only - you need to get a definite answer from someone who is familiar with the detailed design of the equipment. If you send this query to the manufacturer, I am sure that you will get a suitable response - most reputable manufacturers want to make sure that their equipment is installed and operated correctly, as any incidents attributed to their equipment will affect their reputations.

Regards,
Bruce.
 
Hi Bruce,

I liked your explanation. I glad that you and I have the same understanding regarding the Exia rating for the sensor/elements which actually go inside the vessel. Now, I have 2 queries.

1. I have looked for description of this explanation in various standards but no standard explicitly differentiates between the enclosure and the probe part. They all talk about supply and limiting the energy etc. Do you know any reliable technical document which speaks about this?

2. The E&H FTL51 has this certification, ATEX II 1/2G Ex d IIC T6/IECEx Zone0/1. I would like to now if this is Exd, how can it be used in Zone0?
 
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Bruce Durdle

Hi YSH,

The question oh having different certifications for different parts of the same equipment is not specifically set out (as far as I can tell) in IEC60079-0, where I would expect it. However, this standard, does refer to "enclosures" as the basic entity being

"all the walls, doors, covers, cable glands, rods, spindles, shafts etc. which contribute to the type of protection and/or the degree of protection IP of the electrical equipment."

So if you have an item of equipment made up of more than 1 "enclosure" then each "enclosure" can be treated as a separate entity. In the case of a level probe, there is an enclosure for the terminal compartment, and another for the probe (this may be a separate entity completely, with a cable connection, or part of the same physical object but with a physical barrier between it and the terminal compartment).

As far as specifics of any manufacturer's assigned certification goes, you need to ask the manufacturer this. It is common for a manufacturer to assign a wide range of certifications to equipment to satisfy different site standards. The primary document has to be the equipment compliance certificate as this may contain references to specific applications or other details - there is only a limited space on the equipment itself for these details.
Hope this helps,

Bruce.
 
S

S,VENKATARAMAN

Hello

I am S VENKATARAMAN AEE(E) from ONGC and it is 5 years since you posted your query. By now you must have some clear ideas on zones, groups and Ex d, Ex e or other equipment for hazardous locations. If you still have any doubts or queries please contact me through my e mail.

My e mail- [email protected]
 
Hello

Please be careful following zone 1 and zone 2 certifications. They are designed to protect the person who developed them and the manufacturer of the equipment. I have had 20 years experience in the EEX and IS equipment use and sales. For your own protection zone 2 is non reliable as a safety standard if you feel an explosive environment may be present consider it a zone 1 application. Having a zone 2 piece of equipment in operation when the zone changes means you have a problem. Understand also the weight of gases compared to our O2 environment, some are lighter some heavier. This means in containment during operation a gas pocket can be caught, even with venting, causing an area of concern with the zone classification.
 
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