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Anonymous Poster #1

IS Barriers

06/16/2022 10:56 AM

Hi All,

Is it possible to have an IS barrier in a measuring circuit that can be removed without interrupting the circuit? any reference/model/catalog can be provided would be appreciated.

Thanks

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#1

Re: I.S Barriers

06/16/2022 11:58 AM

Not sure, the codes for these are very specific....It seems to me you could have a backup IS barrier circuit, and switch between the two, but without extensive detail, I can't say for sure what provisions would be necessary...

...."An IS barrier limits the sparks and heat in electrical devices that can cause explosions, under normal or abnormal conditions, to a level incapable of causing ignition of a hazardous atmosphere. They work well protecting low-power devices such as instruments, sensors, LEDs and solenoids."... Jan 15, 2018

https://www.controldesign.com/articles/2018/intrinsic-safety-comes-with-requirements/

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#5
In reply to #1

Re: I.S Barriers

06/17/2022 6:45 AM

<...solenoids...>? As in energy-storing devices? In magnetic fields? That create back-emfs when the circuit is disconnected? And sparks?

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#8
In reply to #5

Re: I.S Barriers

06/17/2022 1:58 PM
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#13
In reply to #8

Re: I.S Barriers

07/01/2022 4:42 AM

Intrinsic safety is a method of protection. There is no need for a sparkless switch in the hazardous area on an intrinsically safe circuit, as switches class as "simple apparatus" and are not energy-storing devices.

One can in principle have bare wires in the hazardous area provided protection is in place with a certified safety barrier at the boundary, for instance.

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#2

Re: I.S Barriers

06/16/2022 1:38 PM

Why is it necessary?

Please help the forum provide the help needed.

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#3

Re: I.S Barriers

06/16/2022 2:45 PM

In order to <...remove...an IS barrier...without interrupting the circuit...> one would need temporarily to wire another <...IS barrier...> in parallel with the one that is to <...be removed...> beforehand, thereby obviating the protection to the hazardous area that the first <...IS barrier...> is there to provide.

If the <...IS barrier...> were not damaged, then there would be no need to remove it. If it were damaged, then the circuit is disconnected anyway, so the concept does not apply.

So the answer has to be along the lines of "not without compromising the integrity and the safety of the <...IS...circuit...> and no sane, trained, Instrument Technician would do that".

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#12
In reply to #3

Re: I.S Barriers

06/30/2022 8:10 AM

Some circuits are so sensitive that even measuring them with a digital VOM will compromise them,such as fire protection circuits.

Always consult the Authority Having Jurisdiction.

By the forma of your question,you are not properly qualified to be doing anything with explosive atmosphere circuits.No offense intended ,but getting the required training and experience is vital and life saving,(unless you are trying to get a Darwin Award).

https://www.onlinemasterscolleges.com/resources/darwin-award-winners/

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#4

Re: I.S Barriers

06/16/2022 10:22 PM

Depending on the type of Intrinsic Safety barrier used and how one is used, I know bypassing the IS without interrupting the measuring circuitry is possible but I'll be damned if I will explain how to do this to an anonymous poster. Particularly when absolutely no information is given about why a SAFETY barrier is in the circuit in the first place.

Please, do not kill anybody with this idea.

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#6
In reply to #4

Re: I.S Barriers

06/17/2022 7:13 AM

I agree with you on that.

"What you don't know can hurt you,as well as many others."If you don't know,don't guess.

I suggest he refer to the NEC for reference,but without much experience in this matter,he should refer to the Authority Having Jurisdiction.

Here is a link to the NEC chapter,but this is for reference only,not a recommendation to proceed, with his inexperience so obvious.

https://www.codebookcity.com/codearticles/nec/necarticle504.htm

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#7

Re: I.S Barriers

06/17/2022 7:41 AM

Simple answer--no. As others have said, the barrier is there to limit the energy that can be spent in a fault on the classified side of the barrier. If you were to put two in parallel, then you will have probably exceeded the permissible amount of energy. In addition, I am certain that such a circuit would violate the listing instructions for the barrier and thus be a code violation with a very real risk of liability to the installer and the owner for any subsequent fault.

JMM

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#9

Re: IS Barriers

06/18/2022 1:24 AM

Anything to do with IS barriers should only be done when the protected area is isolated from the explosive atmosphere.

I have worked on IS barriers in coal fired power stations, dirty energy to keep lights on, on Hydrogen, LPG, Flammables and coal dust and also on gas exploration drilling rigs and never would I even contemplate changing out an IS barrier while there is the remotest chance of an explosive atmosphere being present.

Having been licensed and approved to work on Intrinsically Safe devices in a past life I would never risk my own safety or that of others. From your question I would say you are neither of these.

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#10

Re: IS Barriers

06/19/2022 5:21 PM

I can think of one circumstance that might qualify - a single thermocouple wired to the field side of barrier #1 with a parallel T/C connection made from there to the input side of barrier #2 which provides a single signal source for two different thermocouple input devices in the safe area.

Since direct thermocouple analog inputs are high impedance voltage sensing devices, there is negligible load on a thermocouple source and both analog inputs get a valid signal.

Two barriers provide hazardous area side protection for each circuit. Although thermocouples are considered a 'simple apparatus', the hazardous area still needs to be protected during 'abnormal situations' - protection from a fault on the safe side which could feed energy back into the hazardous area through the thermocouple lead wire and generate an ignition source.

The argument against doing such is that it is not typical and for the additional cost of a 2nd T/C element and its field wiring, one has two conventional I/S circuits.

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#11

Re: IS Barriers

06/21/2022 9:21 AM

It is possible, and even desirable on some cases, to have dual-redundant or triple-redundant circuits connected to equipment in the hazardous area via barriers. However, the redundancy needs to be in the safe area - that way, if a barrier needs to be replaced then the surviving part of the other circuitry sustains the hazardous area functionality. Which is not the same as the question that was asked.

Redundancy needs to be considered when the control system is still at blank sheet of paper stage as it is incredibly awkward to add it in after the equipment has been commissioned, especially if the circuit in question cannot be switched off to enable the redundancy to be added.

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