Intrinsic Safety and Simple Devices

[jamieschmidt]

I am working on an installation in a hazardous location, where we are wiring a majority of instruments to intrinsically safe I/O that is located in the hazardous location.

We have a couple of instances where we have level switches that we would like to take into the intrinsically safe I/O. According to information that I can find, this is fine because the switches neither create nor store energy, they are simple devices.

What I am having a problem with, however is that the switches are being provided with explosionproof enclosures and have mechanical parts that could potentially arc or spark when they move, such as a snap switch. Can I still install them as Intrinsically Safe if I use Explosionproof wiring methods at the instrument?

If so, how can I tell for sure that a switch needs to be wired using these methods, and not just intrinsically safe?

 

[bennie]

Re: Intrinsic Safety and Simple Devices

It is my understanding that an intrinsically safe system, is a power source without enough capacity to ignite anything. A switch of any type would work if I am correct with my definition.

 

[hurk27]

Re: Intrinsic Safety and Simple Devices

Bennie

A switch of any type would work

Bennie a switch with the ability to produce a spark would not be intrinsically safe without some kind of housing that would prevent any explosive vapors into it. now a mercury switch would be intrinsically safe as it is sealed.

Also any type of power source can produce a spark when a load is switched so I dont think it depends on the power source like it does in artical 725 it depends more on keeping the spark away from the combustables

[ July 19, 2003, 05:54 PM: Message edited by: hurk27 ]

 

[Ed MacLaren]

Re: Intrinsic Safety and Simple Devices

I would think the switch and enclosure would have to be listed for the Class and Division (or Class and Zone, if you are using the 3 Zone system) in which it is located, even if it is connected to an intrincally safe I/O module that has the required barrier circuit built in.

The barrier only protects against circuit faults.

Ed

 

[bennie]

Re: Intrinsic Safety and Simple Devices

All sparks are not created equal. Ever had fouled spark plugs? The temperature produced at the arc, is directly related to the power creating the arc.

Some arcs will not ignite anything. The temperature has to exceed the flash point of the combustible elements. A 1 1/2 volt battery powered flashlight is an example of intrinsically safe.

Read Article 504.

 

[hurk27]

Re: Intrinsic Safety and Simple Devices

Wow Bennie I learned somthing new.
I never thought that even at 1.5 volts it would be concidered intrinsically safe as we used to use a 1.5 volt battery to launch our model rockets. but 504 does say that the circuit would have to be less than 100 ma and be less than 25 mw
or the passave device has to dissipate not more than 1.3 watts. and be listed

 

[nhee]

Re: Intrinsic Safety and Simple Devices

The I/S barrier limits the energy in the circuit to a value less than that required to ignite an explosion. Any snap switch can be used. The EXP snap switches, if used on the I/S circuits, would be unneccesary.

Note that if the snap switches are used in non- I/S circuits, they will need to be installed per explosion-proof requirements, and will have to be separated from the I/S circuits.

 

[dcsva@aol.com]

Re: Intrinsic Safety and Simple Devices

It is my understanding that as long as the IS Barrier is used, any standard snap switch can be used. We have installed regular limit switches in EXP areas this way. We also installed Gas Seal Offs for the conduit leaving the EXP area.