Intrinsic Barriers

[setchmo 0]

I have a motion detector that controls overhead lights that I need to install in a hazardous area. The detector is a 3 wire, +24VDC, 24V return, and Signal. My question is, do any of you have any suggestions on type or brand? I haven't had much experience with intrinsic barriers. Any and all help will be appreciated. Thanks, Seth

[DanW 41]

The motion detector has to be rated for hazardous area use, explicitly saying so on its tag; including the specific areas, rated as Class x, Div y, etc, along with the agency (FM, typically in the US) that issued a hazardous area compliance approval. Those devices so approved for intrinsic safety have very explicit tables of I/S entity parameters printed in their manuals. The entity parameters are used to select an intrinsic barrier. If your motion detector does not have tagging indicating it is approved for I/S use, or the manual lacks the entity parameters for the device, the device is not rated for I/S use and it cannot be installed in a hazardous area. Edited 9 Nov 2010 by DanW

[Ken Moore 23]

I.S. barriers prevent explosions by ensuring there is not enough current to cause a spark. Because of the very low current ( I believe 100mA is the max.) devices must be designed for I.S. service. You may have better luck with non-incendive devices, but as mentioned by DanW, it must be explicitly rated for the area and use.

[paulengr 44]

The essential detail with regards to the device itself is that it must be incapable of storing any kind of charge (such as a big capacitor) or any reasonably large amount of charge. The barrier as described limits the amount of current and voltage so that even a dead short is harmless. In practice the barriers are a pack of zener diodes (voltage limiting) coupled with dual element fuses (current limiting), and sometimes some additional components but those are the basics. You can find IS barriers almost anywhere...IFM Efector, PepperL-Fuchs, Turck, etc., all sell them.

[setchmo 0]

Thanks for the information guys. I really appreciate it and will now talk to the electrician that ordered this.