Intrinsically Safe equipment but still creating sparks?! 1

[phamgiatoanbk]

Hi all,

I'm working in Oil industry offshore. Here on the drilling rig we use some pressure sensor which is 4-20mA and Intrinsically Safe (IS). Everything is grounded properly... However, one day we observed that some sparks were generated when the sensor cable touch a metal part of another equipment. We are wondering from where could this spark generated?
Any ideas would be appreciated.

Thank,

Toan,

 

[danw2]

I suspect that the spark was shield to ground, indicating a ground potential difference between the shield grounding point and that other equipment.

Control drawings specify the single grounding point for the shield. Is your shield grounded in more than one location? Does your installation match the control drawing?

 

[Compositepro]

"Intrinsic Safety (IS) is based on the principle that the electrical energy in hazardous-area circuits is deliberately restricted such that any electrical sparks or hot spots that may occur are too weak to cause ignition. This is achieved by inserting an energy-limiting interface in the wiring between safe and hazardous areas. The interface passes signals in either direction as required but limits the voltage and current that can reach the hazardous area under fault conditions."

This does not mean absolutely no spark. But, this also does not mean you do not have a problem. The IS applies to the signal wires. If your sparking was to the shield then you have a grounding problem, and it may have nothing to do with the instrument.

 

[itsmoked]

The device being an I.S. device means it won't ignite it's rated atmosphere even if it fails. You must also feed it from a "limited" source so if the wiring fails between the I.S. device and its power supply the failed wire itself can't ignite the atmosphere. Are your I.S. devices fed thru safety barriers as they should be?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LiteYear]

Agree that it sounds like a ground potential difference, and if the spark was visible the energy probably came from a different device - the shield is just providing a path to ground. Do you have any big switching loads like variable speed drives? They could be causing uncontrolled ground currents.