gas detector intrisically safe??

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buddhakii

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Littleton, CO
Hello fellow sparkies. I have a couple question regarding a gas detector I am installing in a class 1 div. 1 area. The detector will be installed in the classified area but the moniitor is outside. There is a 5 conductor twisted shield that goes from the detector to the monitor. If I recall correctly it's 5v, tx, rx, grnd, and one other I cant recall right now.
First question: Do I need a seal off going into the detector?
Second question: Would this be considered an intrisically safe circuit? I have an intrisically safe analog circuit that goes to a pressure transducer, and one going to a float switch. Both of these are in seperate conduits in order to seperate analog from discreet. I would like to run the analog cable for the gas detector with the pressure transducer, but I know it's not allowed to mix non-intrisically safe with intrisically safe circuits. I have a spare that I can use, but I would like to keep it as a spare.
Thanks for all your help in advance.
 
#1. Don't know for certain without more details. If it is listed as intrinsically safe, no. If not, a required seal is conditional under 501.15(A) and there are also exceptions thereto.
#2 Since this application does not seem to use any "simple apparatus", all apparatus (detector and monitor) must be listed as intrinsically safe.
 
1) What is the mfg/model of the gas detector and monitor? The manual for the gas detector will cover installation requirements, such as whether the instrument is listed for and can be installed as intrinsically safe; or if not, whether the detector is factory sealed (would also be stated on the label), or requires external sealing.

2) First, let me say that I see no reason to keep your I.S. analog and I.S. discrete circuits separate. As long as they are all properly installed as I.S. circuits, they can be run with each other, ditto if they are both not I.S. Point being that if one is I.S. but the other is not, they can't be run together as you already know.

(I have seen several installations that insist in keeping 4-20mA DC analog circuits separate from 24vdc discrete circuits for no other reason than they are analog vs. discrete, which is totally unnecessary and wasteful.)

Based on my prior comments, if your detector is NOT an intrinsically safe model with an approved installation drawing which you would follow, then it must be separate from your other circuits which ARE intrinsically safe. If it IS an intrinsically safe device and circuit installed per the approved drawing, you could even go as far as combining all three of your I.S. circuits in the same conduit.
 
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I will get back to you with the mfg/model. It's a requirment to keep analog and discreet runs in a seperate conduit though. Read through the installation drawings for the gas detector and I didn't see anything that said it is intrinsically safe so it looks like the spare conduit I ran is no longer going to be a spare. It's not factory sealed either so it looks like I need a seal off. I was hoping to get around that cause it will have to be a pvc coated seal off. Thanks for the replies.
 
buddhakii said:
I will get back to you with the mfg/model. It's a requirment to keep analog and discreet runs in a seperate conduit though. Read through the installation drawings for the gas detector and I didn't see anything that said it is intrinsically safe so it looks like the spare conduit I ran is no longer going to be a spare. It's not factory sealed either so it looks like I need a seal off. I was hoping to get around that cause it will have to be a pvc coated seal off. Thanks for the replies.
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The manufacturer usually have specific installation instructions for anytihng that is intended to be installed in Cla. I, Div. 1 locations. The device - sensor if I understand you correctly - would have the approval agency's logo and label. If it is IS, the label would say so. Even if it is IS boundary seal may be required between Classified and Nonclassified transition. No NRTL label = no install, UNLESS the Owner gets a pass from the AHJ in writing.
 
It's definately rated to be installed in class1 div.1. I will be installing required seal offs in all the transitions from class. area to non-class. area. Did not see anything on the detector that states it is IS though so I guess I will have to put a seal off before the detector. As I stated earlier I was trying to get around it due to the fact it will need to be pvc coated.
 
buddhakii said:
It's definately rated to be installed in class1 div.1. I will be installing required seal offs in all the transitions from class. area to non-class. area. Did not see anything on the detector that states it is IS though so I guess I will have to put a seal off before the detector. As I stated earlier I was trying to get around it due to the fact it will need to be pvc coated.
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A seal at the detector may not be required as I mentioned in my first response. See 501.15(A)(1) and its Exceptions. Without more details on the "detector", that's all I can tell you.
 
It is interesting that many gas detectors work by combusting (oxidizing) the gas and measuring the heat produced to arrive at the level of gas in the area. They use some type of catalytic burner along with a flame arrester to prevent the ignition of the atmosphere if it would happen to be within the flammable range.
 
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