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Topic Title: ATEX Intrinsically Safe Wiring
Topic Summary: Supplying equipment that is Ex d/e with through an intrinsically safe barrier.
Created On: 28 July 2012 09:04 AM
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 28 July 2012 09:04 AM
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markthemariner

Posts: 11
Joined: 14 May 2010

I was wondering if somebody could put some light on an issue I have come across.

At my place of work we are doing some alterations regaring a DSEAR survey that was done to some of the plant equipment. In particular there is a situation were an Ex d piece of equipment is being supplied by a intrinsically safe barrier in a panel in a safe area out to the equipment. This is all working correctly with no issues.

It was decided that this was not correct and had issues with simple appartus so the intrinsically safe barrier circuit is to be removed. The alterations are to be done in the panel, altering the cable and removing the barrier. Now to me this is incorrect and the circuit could stay the same without any issues. If a circuit is intrinsically safe you could use any piece of equipment because the energy is controlled by the i.s barrier in a safe area. So in my mind an i.s. barrier is perfectly acceptable supplying an Ex d/e piece of equipment as it is the highest form of electrical protection. Would anybody agree with this.

I know ATEX regulations can be a mine field but I would appreciate your input and advice.
 28 July 2012 09:27 AM
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Jobbo

Posts: 912
Joined: 08 July 2010

What is the type/rating of IS barriers located in the panel? What rating is the flameproof enclosure and does it have any special conditions of use? What zone or EPL is the location in question and what is the substance

More information is required to give a accurate opinion

Regards

Jobbo
 31 July 2012 02:17 PM
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ATEXConsultant

Posts: 2
Joined: 31 July 2012

Hi Mark,

An IS barrier should only supply and IS field device such as a suitably certified IS sensor, or a suitable simple apparatus. You should not supply an Ex d piece of equipment with an IS barrier.

Also, the combination of an IS barrier and an IS field apparatus should be carefully looked at with for example the standards EN 60079-25 and EN 60079-14 if in force where you work.

A barrier does control how much energy it provides but within limitation: the barrier installation instruction must be followed, the circuit and field apparatus must be compatible...

Kind regards

Vincent
 02 August 2012 10:42 AM
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markthemariner

Posts: 11
Joined: 14 May 2010

Hi Vincent,

Thanks very much for your response to my question.

I have done the CompEX course but wasn't sure of the regulations regarding this. Even though I passed the course I still find I have to refer to my notes and books to get answers to the more complex situations ATEX brings.

I was looking for some data to respond to Jobbo's reply but you have answered my question. I still don't understand why you can't feed something via an IS barrier to say an Exd piece of equipment if it will work. Surely you are protecting yourself even more, wasting money I admit but the protection is doubled if you like. But if the regulations state you can't then that's what I wanted to know.

Anyway this means some drastic changes in the panel wiring but needs must )

Thanks again.

Mark.
 02 August 2012 12:49 PM
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Jobbo

Posts: 912
Joined: 08 July 2010

Mark

As vincent pointed out, you cannot connect a device which is certified as Ex d only on to an IS only circuit. Any components connected to an IS circuit downstream of the barrier or isolator must be certified as IS

But and this is why I wanted more information, if you are referring to a device certified as Ex d [ia] or Ex d [ib], the device itself can supply an energy limited output, as well as operate with a flameproof main powered circuit. The [ ] indicate that the device also contains auxiliary components and therefore dual certified. It is essential that the conformity certificate along with any special conditions of use is followed

Regards

Jobbo
 02 August 2012 01:04 PM
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Jobbo

Posts: 912
Joined: 08 July 2010

I should of pointed out that an intrinsically safe circuit relies on the control of the energy in the circuit exposed to the hazardous substance. This requires the voltage/current in the circuit to be known, along with the capacitance and inductance values. Unless you have this information for the Ex d equipment, you cannot be sure that the total energy stored in the circuit is limited to a safe operating level

IS barriers and isolators are certified as safe with a set max circuit capacitance and inductance value and part of the design is to ensure that the safe limits are not exceeded

Regards

Jobbo
 15 August 2012 03:28 PM
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ATEXConsultant

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Joined: 31 July 2012

Hi Mark,

I am happy to hear that my answer helped.

Simply put, an IS barrier only "protect" within "its ability". When you connect a non IS device outside the barrier "ability" you don't really protect. Furthermore you invalidate the barrier ability to "protect" suitable IS device. (I would not recommend to keep the barriers that where used to power the Ex d device)

I have used quotation mark because this is not proper ATEX terminology. To understand in depth you have to go to the standard.

If you have more question, please, do not hesitate to contact me directly.

Kind regards

Vincent
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