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Tuesday, June 18, 2019
The Automation Safety Community Forum.
does Ex d Ib need IS barrier?
does Ex d Ib instrument need IS barrier?

Hi everybody,

I have a gas detector Ex d ib.

Do I need to install an intrinsic safe barrier on the 3 wire power supply? or the ib only refers to the connection between sensor and transmitter?


The power will have to cabled to the gas detector as explosion proof.
Unless the manual says something about it being loop powered.
Confirm in the manual that the detector has a barrier for the sensor or that it must be explosion proof wiring.
Maybe only the detector outputs are IS.


thank you for your answer.

Yes the manual shows a barrier inside the device, on the sensor side. And no it is not loop powered (3 wires).


The "d" indicates flameproof (explosionproof) in Zones 1 and 2 using appropriate wiring and sealing. The "ib" indicates intrinsically safe in Zone 1 and 2 using regular wire and a barrier installed in a safe area.

Refer to the Control drawing for the gas detector. The control drawing can often be found in the back of the installation manual, on the manufactures website, or by contacting the manufacture.


if I understand well your answer, the device can be used as explosion proof OR as intrinsic safe, depending on the way it is wired. So it is not mandatory to wire it as IS.

What surprises me though is that the technical specifications mention in rush current of 1.6 A, which can not be achieved by an IS barrier. Unfortunately, supplier manual is not that clear regarding wiring, but it doesn't specify IS power supply.

I have read a lot of posts regarding EEx d [ia] device but I still find it hard to understand what the [ia] refers to...

Thanks for your help.

The device has to be explosion proof because of it's power requirements. But the sensor and signal wiring(?) can be IS.

I have seen this with a 4 wire ultrasonic flowmeter, where the power wiring and transmitter enclosure were explosion proof but the signal output with a barrier was IS.

Yes, you are totally right.

I just had a reply from the supplier: "The DM-700 is not Ex ia. The only section of the unit that is intrinsically safe is the plug-in cell, which allows for the safe removal and replacement of the plug-in cell in an explosive environment, the rest of the unit is only explosion proof"

Thank for your much appreciated feedback!