Basic difference between Zone-2 and Zone-1 equipment

I

Ingrid M. Gilstrap

Bruce,

Thanks for your response to my question about Zone 1 flameproof approved product use in Zone 2 areas. It's been helpful. I like your site and exchange of information.

Thanks,
Ingrid
 
Gerry,

I am at Goro Nickel Project new Caledonia. Some one has installed Ex nR luminaires in zone 2 areas. They have now realised that there is a statement at the bottom of the CE that after install the conditions of install call for enclosure to be pressurised for 3kPa after a period of 27 seconds the internal pressure shall not be less than 2.7kPa - a lot of lights for this plant for them to go back to - what is your opinion?

Regards,
Phill
 
In Ex d the symbol "d" is derived from the German word "Druckfeste kapselung". Some people use the term explosion proof synonymous with the flame proof encloser.

The flame path is the shortest path along a flame proof joint from the inside to the outside of an encloser. Normally flanged covers, spigotted cover and the threaded cover are used in flame proof enclosers. The flame path shall be

Min 12.5 mm for IIA & IIB enclosers.
Min 25 mm for IIC enclosers.

The flanged joints are not permitted in IIC areas. Threaded joints shall have more than 5 engaged threads and an axial length of 9mm minimum. This is applicable for cable glands as well. The gap in the flameproof joint is the distance between two mating surfaces of the encloser. The maximum gap permissible for flame proof joint is

0.20 mm to 0.40 mm for IIA enclosers.
0.15 mm to 0.20 mm for IIB enclosers.
0.10 mm to 0.15 mm for IIC enclosers.

The different methods are adopted to safe means of connecting the electrical equipment with a flameproof encloser to the external circuit. the Indian standard makes it mandatory to have an Ex d terminal chamber, either integral to the housing or as two separate enclosers joined together by means of sealed or moulded bushings.

In European standard, the use of Ex e terminal chamber interconnected to Ex d encloser is permitted. The connecting wires from the main enclosers are passed through sealed or moulded bushings to the terminal chamber. In American standard the metal screwed conduit is directly connected to E x d encloser.

All protection techniques are not suitable for all zones. Following is the recommendation for different zones.

ZONE 0 Ex ia
ZONE 1 Ex ib, Ex d, Ex e, Ex p
ZONE 2 Ex n, Ex o, Ex q
 
P

Paul Spresser

The Flameproof (Ex d) technique allows the use of any commercial electrical or electronic equipment inside of the Ex d enclosure. If the atmosphere becomes explosive and seeps into the enclosure, a spark will only ingnite the mixture inside the Ex d enclosure because the combination of the long joint length (flame path) and the small gap (<<MESG - the maximum experimental safe gap) cool the exhausting gases to below the ignition temperature for the group of gas.

The Ex e technique simply ensures that a spark or thermal heating which will ignite an explosive mixture is most unlikely to occur in the first place. Improved terminal types are used to minimise the likehood of terminations loosening and marking fortuitous contact with other conductors, terminal types, wire gauge and current combinations are limited to certified combinations to maintain the temperature rating, the enclosure has a minimum IP (ingress protection rating).

Ex d enclosures do not need one to be safe - simply for normal electrical reasons, and the enclosure parts are all boded to the system earth, including the gland plate, the door and any other extraneous metal part. Ex e enclosures are usually sheet metal or plastic, with the exception of motor terminal boxes which some may mistake as being flameproof when they are not. They are simply of robust construction.

The standards Australia document - HB13-2007 -0 available from SAI Global as a PDF document - is an excellent resource for coming up to speed on IEC (or CENELEC - that is Europe including the UK, or Australian/New Zealand requirements) which are reflected in most of the world except the Americas.

As to the Zone 2 example with the gas leak, the Ex d motor is certified for Zones 1 and 2. It depends on the gas leak as well. Is this something that was allowed for in the original hazardous area classification - such as the venting of a PSV - or what this a catastrophic failure?

The classification of hazardous areas does not take into account catastrophic failures but does include a study of safety devices (the action of which is classed as "normal operation").

Also note - the definition of Zone 1 includes the presence of an explosive atmosphere - ocasionally. From personal experience in testing such equipment (explosion and flame transmission testing of flameproof equipment - including motors)a properly designed Ex d motor which has been certified as complying to an IEC standard (or any national clone thereof)would most likely not cause an issue with a one off catastrophic release of flammable gases.

The real issue is that such a release will cause the orignal hazardous area classification to go out the window, as the hazardous area will (however momentarilly) expand to include equipment and installations never intended to be in an explosive atmosphere - and will most likely find a source of ignition there.

Most Ex protection types have belts and braces built into them in terms of the methodology behind the technique and the requirements of their respective product standards. An inadvertant release of a flammable gas about a well maintained, certified Ex d motor would be the least of my worries.

I hope this clarifies rather than confuses.
 
Hi all,

I am working as Engineer with one of India's Largest Power Generation Company NTPC Ltd. I am having a query regarding material of junction box that is to be installed in HFO and LDO Pump House Area. There are two options available with us- One is made of FRP (Fiber Glass Reinforced Polyester) and other is made of Cast Aluminium Alloy LM6.

As per information provided by vendors and other sources, Cast Aluminum made Junction Boxes provide Ex-d protection whereas FRP Junction Boxes can provide only Ex-e protection.

However, We are not able to find any authenticated 3rd party document which which substantiates materials that can be used for construction of Exd protected Junction Boxes. In short we want to ensure that Exd Junction Boxes cannot be made with FRP.

Also, from all the answers above, I could not make out what is the advantage of Exd over Exe if these are to be used in HFO and LDO Pump House Area.

Please help.
 
Hi there,

You are making things to complicated. First look at the area classification (Zone 1, 2, 3) of the pump stations to see what is the minimum requirements. Exd or only exe. Then find a manufacturer for exd or exe junction boxes. If you need to install exd boxes the manufacturer will rate these boxes so you do not need to concern yourself with the material it is made of. The same is true for the exe boxes. Your concern is only with the rating of the box. If the manufacturer made the box out of a certain material and give it a exd rating then you can be sure it is exd, since he have to comply with various regulations in order to approve these boxes as exd or exe.
Anyway I have personally never seen a exd rated JB made out of anything else than thick Aluminum. Boxes with exe or IP rating is normally made from FRP.
 
D

Dave Anderson

Exd and Exe are designed to be used in zone 1 areas. Because of this they can also be used in Zone 2 areas.

If you have a small plant it is safer to use the superior designs in Zone 2 hazardous areas. if you have a large plant it may be cost effective to use equipment rated for Zone 2 only in Zone 2 areas.

With the smaller plants if you use equipment with different ratings you can guarantee that sooner or later an inferior design will be fitted into a zone 1 area and have to suffer the consequences.

On small plants where the cost saving is not so large it is safer to use equipment rated for Zone 1 in both zones 1&2.
 
A

Asok Kumar Hait

I will try to give you some insight into the subject.

Since you are working in a power plant which basically doesn't deal with hazardous area, your engineering department may not have people who knows how to classify a hazardous area. If you don't have any information then just assume that your area is Zone-1 hazardous area.
Now for Zone-1 hazardous area both Ex'd' and Ex'e' protection techniques are suitable.

If you are using Ex'd' junction box then normal material is cast aluminum. The reason is for Ex'd' protection, the housing has to retain the explosion within the box and that's why it has to be strong thick metal. If you make an Ex'd' box with carbon steel or stainless steel that will be very heavy. This is the normal reason Ex'd' boxes are generally built with lightweight strong Aluminum material. Now it should be clear to you why FRP can't be used as a material for Ex'd' box.

FRP or normal carbon/ stainless steel is generally used for Ex'e' junction boxes. Ex'e' is a protection technique where basically protection is achieved by "increased safety" design. For an Ex'e' box all the items inside the box has also to be Ex'e' certified. For a junction box there are only terminals inside and this is very easy to achieve.

For a junction box we normally prefer Ex'e' because of few reasons:

1. Lower cost than Ex'd' box;

2. For an Ex'd' box before opening the box, you need to shutdown the power. No such limitation for Ex'e' box;

3. For an Ex'd' box if you want to make additional cable entry at site you can't do that. That will nulify the certificate of the box.
Therefore, for Ex'd' box you have to be very careful. You need to define correctly no. of cable entry inside the box and size of the cable glands before buying the box;

For Ex'e' box if your cable size changes or you want to make additional cable entry - that is possible at site. This is one of the most important reason people normally prefers Ex'e' over Ex'd' junction box.

However, there are situations where Ex'd' is the only choice. For example if you have to install an equipment inside the box which is not Ex'e' certified (e.g. a converter or an isolater), then you have to use Ex'd' box only.

Material wise FRP is a good corrosion resistant material. But you have to consider UV resistant material in India. FRP is not as durable as SS316. Therefore, in offshore industry (salt laden atmosphere) many people just use SS316 for longer life.
For your application - FRP Ex'e' is technically absolutely suitable. Only take care that the terminals inside JB must be Ex'e certified and the cable glands also must be Ex'e' certified.

Regards,
Asok Kumar Hait
 
Hi guys,

I would like to know whether we can modify non-ex compressor to ex-type by simply modifying the termination and terminal box material.
 
B
No - for any form of explosion protection you need to have the equipment certified which is quite a process
If you want to get it rated as flameproof Ex d you need to meet restrictions on flange sizes and clearances, and the equipment has to undergo a series of tests where the flammable atmosphere inside the enclosure is deliberately ignited. For increased safety Ex e things are not quite as bad but you do need to meet requirements about the termination materials and clearances, as well as ensure that any motors have suitable protection.

Bruce.
 
Z

Zacharia, Tomy

Bruce is right, No equipment is permitted to be modified or components substituted. If the equipment is already certified, it automatically loses certification, and unless tested as per code in an approved laboratory, equipment cannot be modified and be compliant.

Regards,
Tomy Zacharia
 
N

Nathan Lamont

I also have to thank you for helping to understand the zoning and requirements... I know this is a bit left field but does anyone know how the ratings work with the belts between the Motor and Pump?

As I have arranged to get made for me a Zone 1 Gas Group IIc T6 compliment motor (Ex d) but I have had several ask me about the drive belt, but I cant find anything on it to meet the heat specification or any other rating!
 
B
The current international rating system (Ex d, Ex e, etc) refers only to electrical equipment. However, the European ATEX rules require that all equipment that is capable of ignition has to be certified.
I'm not familiar with any codes or standards relating to mechanical equipment but overheating belts are certainly a possible source of ignition - as a minimum I would suggest you apply the same temperature rating to the belt as you would to the motor surface. If you are asking for a T6 motor, this means that the maximum surface temperature of the belts under worst-case conditions should be below 85 deg C.

Another possible cause of ignition from belts could be electrostatic discharge.

I've just googled "ATEX drive belts" and got quite a few hits - it appears that certified belts are certainly available. Whether or not the ATEX requirements for mechanical equipment are required in your area, it would be good practice to use them if they are suitable.
 
A

Anar Guliyev

Please tell me somebody when I should use Ex d or Ex i? For example, I use Ex ia device, do we need the additional Ex d certification or vice-versa?
 
B

Bruce Durdle

If you have an Ex ia device, you can use it in Zone 0 - an Ex d device can be used only in Zones 1 and 2. So you don't need Ex d certification if you have Ex ia.

Bruce.
 
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