Area Classification Dilema

HI FRNDS

AREA CLASSIFICATION FOR OUR PROJECT IS DEFINED AS

CLASS 1, ZONE 1, GAS GROUP II B, NOW TO SELECT INSTRUMENTATION SYSTEM WHICH ONE SHOULD I SELECT Exd(FLAMEPROOF) or Exib TYPE (INTRINSIC SAFE) PROTECTION ?

BECAUSE AS PER NEC BOTH CAN BE USED FOR ZONE 1


ALSO WATS THE DIFFERENCE BETWEEN BARRIER AND ISOLATOR?

REGARDS


JOSE JOHN

Check here http://www.cdynamics.com/class-I_specs.html
BUT... you also need to check with your government and see you local and federal codes

To me....Intrinsic safe barrier is something that will open up when there is a short and not allow the 'safe end' to generate a spark an isolator does not have to be for protection it can be for noise

If the choice is available I would choose Is as opposed to flameproof. IS is usually cheaper and is much easier to implement. However, IS is limited to low power devices so you can't get an IS motor, for example. Also, an IS barrier need to be matched to the device it is protecting. Basically this is done by evaluating the 'entity parameters' of the barrier and device to make sure the barrier provides adequate protection.

I think the correct term relative to IS is barrier. An isolator is usually a device that will provide some amount of separation between two systems. You can get IS isolators, which combine the functions of an isolator and an IS barrier. However, not all isolators are barriers and not all barriers are isolators.

As a side note, the simple IS barriers are usually a combinations of zerner diodes and resistors. These insure that, no matter what the input voltage to the barrier is, the output voltage will not go above a certain level and the output current can't go above a certain level even given a short circuit. There are some active barriers on the market but I have never used one.

Keith

In today's world, there are two basic types of I.S. barriers, the zerner type which Keith mentioned, and the galvanic isolation type, which are often called I.S. isolators. This may be what the OP was looking for when he/she asked the difference between an isolator and a barrier. I know that Germany requires the galvanic isolation type in Zone 0, other governments may have local requirements as well, so I would check before purchasing.

The galvanic isolators are more costly up front, but I believe they have a lower total cost. The zerner types have to be maintained, the path to ground MUST be tested at least once per year.

I work at a facility that has both Exp and I.S. all of our older equipment is Exp, and anything after the mid 90's is I.S.. I much prefer I.S.

If you use I.S. then rigid conduit with seal-offs are not required, you can run all your instrument wiring in cable tray.

I used several different brands of barriers over the last decade, but P+F is now my preference. http://www.pepperl-fuchs.com/


What does intrinsically safe mean?

* The voltage and/or current (power) in an intrinsically safe circuit are so low that a potentially explosive atmosphere cannot be ignited as the result of a short circuit, interruption or earth fault.
* The ignition energy of any spark that may arise is smaller than the minimum ignition energy of the potentially explosive atmosphere.
* Neither a spark nor a thermal effect will ignite the potentially explosive atmosphere.