intrinsically safe circuit

[Ken10]

Is the 1.2k pot intrinsically safe in a Class 1, Div. 1 Group g hazardous location?

Sorry about the wall paper in the attachment.

Ken10

 

[DRWeig]

Not as you have shown it in your drawing.

Potentiometers do qualify as "simple apparatus," but no device ever is intrinsically safe without an intervening intrinsic safety barrier located in a safe area or an explosionproof enclosure. While not actually mandatory, you should also insure that the following are not exceeded with your pot in sercvice: 1.5V, 25 mW, 100 mA. You may be able to get by with an isolating intrinsically safe power supply, but I would strongly recommend that you talk to the tech support engineers at MTL or Pepprl & Fuchs before making such a decision.

A strict interpretation would allow these values to be exceeded by a simple apparatus, since they do not "produce or generate" voltage, current, power. A pot certainly does not store energy, nor produce or generate anything on its own. The intent of the limits is for stuff like batteries and capacitors. However, many code authorities interpret those limits to include voltage, current, and power that are supplied to the simple apparatus when in use. Those folks may be wrong, but they have jurisdiction.

Get a barrier in there, or an isolating resistance mirror. You'll have to compensate in your design for the characteristics of the barrier. Easier would be a small explosionproof enclosure with the pot mounted and wired by a UL certified hazardous location panel shop. I recommend Akron Electric -

http://www.akronelectric.com.

You'll still have to wire in appropriate conduit with seals, but your circuit already designed will not need changing.

See attached for a primer.



Best to you,

Goober Dave

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[Ken10]

Thank you for the replys.
Ken

 

[itsmoked]

"produce or generate" voltage, current, power.

Should probably read "store ,produce, or generate, voltage, current, or power"

'Store' would include capacitors, inductors, or batteries.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DRWeig]

Correct-o-mundo, Keith.

Thanks!

Best to you,

Goober Dave

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[itsmoked]

Hi Dave,

We developed an I.S. product that was was battery powered by four lead acid batteries. We had lots of fun dealing with those ramifications.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DRWeig]

Lordy, Keith! I don't even want to think about that. Standard hard-wired controls are stressful enough when I start thinking about blowing stuff up.

"The goal of every engineer is to complete his career without being blamed for a major disaster."
--Dilbert, speaking at career day to a class of little kids.

Best to you,

Goober Dave

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