Area classification

These are different types of protection schemes for instrumentation devices and wiring techniques hazardous locations.

IS is for Intrinsic Safety. This is a total wiring solution that requires the field device the wiring and a barrier/isolator to be matched thus limiting the amount of available energy in the hazardous areas this would include wiring and the final device.

For IS you must have what they refer to as entity parameters which are voltage, current, capacitance and inductance for the end device and capacitance and inductance for the wiring. These are used in selecting the barrier or isolator to be used for the circuit. This method is easier to install and maintain from servicing the devices. It does require that the technicians understand the principle and do not jeopardize the installation by installing devices that would invalidate the IS circuit

IS can be used in Class 1 Div 1 as well as Class 1 Zone 0 installations without the need for additional Explosion proof protection.

Ex d is a method that uses an enclosure to contain an explosive mixture within itself to protect the outside environment from the risk of the ignition. This is also referred to as flameproof in IEC. This method can be used in Class 1 Div 1 and Class 1 Zone 1 areas but not for Zone 0. This is heavier and generally will have additional labor hours for the installation required for the installation of this method.

References on these types of protection can be found at www.rstahl.com also a known as an expert in explosion protection or through FM, IEC standards groups as well.

ral412

I S Intrinsic Safe

Ex d Explosion Proof

IS ( Ex ia) is used for CL 1Zone 0

Exd for CL 1 ,Zone 1 Application

Ref to NEC 70 ARTICLE 505, for further Info.

Regards

Jose

if u want to know about I.S, U should start by asking " what is hazardous area and safe area" as y'll find these terms in chemical/oil/gas/petrochemical industry.

If u probe further, u'll see that any area in field in the above desiganted industry has explosive gas mixtures which is capable of getting ignited due to various causes. I'm not elaborating on them now.

to safeguard/eliminating the chances of explosion in these explosion prone areas u've to be careful about the various sources present in the areas which may cause explosion, since u cannot eliminate the explosive gas mixture, u concentrate on the chances of explosion by various means.

the most common of them are;

I.S.= INTRINSICALLY SAFE, where u restrict the energy supplied to the field to a level that they are insufficient to cause any explosion under any fault condition.

this method calls for ther use of Isolators/Barriers, and the most cost-effective means of protection.

its a very brief explanation of an elaborate method.u can also read EN60079-11 FOR AN INDEPTH KNOWLEDGE.

THE SECOND METHOD:

Exd: =explosion proof also called Flame proof (EN60079-1)

It provides enclosure to house equipment which when subjected to an internal explosion will not ignite a surrounding explosive atmosphere.

It is a costly method as compared to I.S. and less popular I believe after the advent of I.S. concept.Also the flexibility provided by I.S methods in commisioning makes it a ideal choice.