Hazardous Area Ethernet


Thread Starter

Brian M.

Hi List,

I am currently investigating an application using an Industrial PC in a purged enclosure for use in a hazardous area (Zone 1 or 2). We will be using 2 network cards, one to communicate with a PLC and
the other to the factory MIS system both of which reside in the safe area.. The problem is as follows, Due to budgetary restraints we cannot go down the fibre-optic route. What I am hoping to find is some kind of optically isolated hub that we could control the supply to through a contact on the pressure monitoring device in the purged enclosure. Does anybody know of such a device or could they recommend another solution.

Many Thanks

Brian M.

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Since all UTP is transformer isolated, I doubt you'll find an optically isolated hubs - if you did the volume would be so low you're talking high, high price.

What about just putting a short (1 meter) fiber link in your panel? You'll still need to get barriers for the power supply to the field FO-UTP media converter. Would you be able to find barriers for UTP? I rather doubt it.

What about wireless Ethernet? 802.11 is becoming rather common.


Lynn August Linse, Senior Product Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected] www.lantronix.com
Tel: (949)300-6337 Fax: (949)453-7132

Curt Wuollet

Hi Brian

10BaseT (and probably 100BaseT) ethernet is already transformer isolated. You might have to check if the standoff voltage rating is high enough or whatever but the isolation is already there. The signal voltages and energy
available on the link might be a problem, but it should be specified. It wouldn't surprise me if Black Box or someone makes a passive isolator for lightning protection also.

Hope this helps

Fiber optic is your best solution through the hazard then back to hardwire F-O is not as expensive as you may think, first use a F-O ethernet card then standard cable glands for feed through enclosure.

Darold Woodward

This is a life-safety issue. The following statements are general discussion of the topic and do not constitute a design or a basis for a design. Your installation should be designed by a licensed engineer in your area and properly inspected to help verify code compliance.

I think that you should review the requirements for the hazardous location that you are working in. If you are using a purged enclosure, it may not necessary that all circuits be intrinsically safe or cutoff when the proper wiring/raceway construction is used. You may only need to enclose the cable in conduit until you leave the hazardous location and seal as required.

Whoever has shorted your original budget appears to be exchanging some $$ for the safety of the operators. I bet the operators would prefer fiber-optic cable. It is possible to buy small fiber-optic transceivers that can be mounted in the enclosure and in a non-classified area. This way you only need to run a very small amount of fiber.

I suggest that you contact a licensed PE that
understands any local codes that also apply. There are also excellent NFPA documents that describe hazardous location installations in great detail and provide good guidance on installations and properly rating rooms, enclosures, and such. For example, I used the NFPA document on hazardous locations in wastewater
treatment plants and found it to be helpful. It may be possible that by more accurately rating the room (or providing some ventilation for the room, etc.) that you can reduce the rating and thereby mitigate the hazard.

Sorry about the lecture, but it is a matter of life and death that issues like this are resolved properly. I hope that this discussion is of some help.

Darold Woodward PE
SEL Inc.
[email protected]

Mark Svoboda

Seimens has a Class 1 Div 2 rated hub also. Three ports 9 pin and one port fiber optic.

Another company I like and am going to use in a Class I Div 2 grp C&D area for a Gas Chromatograph
ethernet is RJLnxx ENHSDURR5 cost about $560.
contact for www.rjlnxx.com or 800-225-7724.