Type "J" Thermocouple

[jcross]

Are Type "J" thermocouples considered a non-incendive device, along with the associated field wiring? If so all I would have to comply with is 501.4(B)(3)? If not looks like I would have to comply with 501.3(B)(6)? These are to be installed in a Class 1 Div 2 Group B area. Any help on this is appreciated.

 

[rbalex]

Re: Type "J" Thermocouple

I'm assuming you are operating under the 2002 NEC.

Thermocouples, in general, are not heat producers and are considered nonincendive equipment by definition[500.2]; however, you will need a manufacture's "control drawing" to properly document it.[500.4(A) and 500.2]

Another, issue to consider is that sealing requirements in Sections 501.5(B) and 501.5(E) don't necessarily disappear - especially at boundaries.

 

[friebel]

Re: Type "J" Thermocouple

As you are aware, a class J thermocouple will only produce milivolts of voltage, and your question is, "can these thermouples be installed in a Class1,Div.2,Group B.area.
I will give you an analogy of a motor in a Class 1, Div 2, Group B location.The NEC will allow you to install a non-arcing motor in this location. So a three-phase, open-motor with no arcing devices can be installed in a Class 1, Div 2, Group B area and this motor can have a voltage such as 460, 575, or even higher voltage.
The one thing that you need to be concerned with is the temperature of any device that you put into this classified area. The temperature of any device cannot exceed 80% of the AIT,(auto-ignition temperature) of the chemical you are dealing with.So, for all of this long-winded talk, yes, a Class J themocouple can be installed in a Class 1, Div. 2, Group B.location.

 

[jim dungar]

Re: Type "J" Thermocouple

The thermocouple itself may be installed in a classified location, but you may not connect/wire it to just any controller. Make sure your controller is capable of properly limiting the energy to a faulted probe. You may have to add an intrinsically safe barrier between the controller and the thermocouple.

[ August 21, 2004, 01:03 PM: Message edited by: jim dungar ]

 

[jcross]

Re: Type "J" Thermocouple

Thanks guys for all the info. I'm fairly new to this forum and try to check it out daily. There is a lot to be learned and a lot of good information is posted here daily. Many Thanks..