Class I Div I, Low voltage cabinet installation (intrinsic safety)

MWagner_MA

Member
Location
Hartford, CT
We are designing in a IOT device into a Class I Div I Zone 1 IIc T4 location. Because it's a wireless device using small antennas, it is preferred to use a non-metalic cabinet as we have done for standard commercial installations.

The NEC requires metalic conduit as our 12V power is high enough in power to require protection. Highest voltage is 12VDC. We are designing our own I.S. barrier.

Question: Can we attach metal conduit to a suitably rated non-metallic cabinet? If so, what fittings are available? It isn't explosion proof, but we just need to seal out water as it is an outdoor installation. The box will have a vent as there is a barometer inside.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I must confess I have no idea what IOT means in the context of your post; however, the description of your application indicates you are designing utilization equipment [See Section 100 for the definition] that would be subject to Section 501.135(A) unless you could qualify it under Article 504. In either case, you will have issues with having your product identified (another defined term) for the location. A self-designed IS barrier is questionable.

BTW the voltage level, as such, is irrelevant.

All that said, IF you actually do qualify as an intrinsically safe system THEN you don't need to worry about metal conduit either.
 

MWagner_MA

Member
Location
Hartford, CT
IOT/ Utilization Equipment

IOT/ Utilization Equipment

I must confess I have no idea what IOT means in the context of your post; however, the description of your application indicates you are designing utilization equipment [See Section 100 for the definition] that would be subject to Section 501.135(A) unless you could qualify it under Article 504. In either case, you will have issues with having your product identified (another defined term) for the location. A self-designed IS barrier is questionable.

BTW the voltage level, as such, is irrelevant.

All that said, IF you actually do qualify as an intrinsically safe system THEN you don't need to worry about metal conduit either.
Thank you for the reply Bob. IOT stands for "Internet of Things". This is equipment to facilitate connection of modern sensors and controls to the internet (the cloud) for everything from personal electronics to industrial equipment. It seems we will be able to qualify under 501.135(A). The confusion about the conduit is that most "intrinsically safe" barriers are for wiring of sensors which are MUCH lower power than our device. Furthermore, you can't just run bare 12V wiring capable of carrying 1.5A as an accidental short will cause a spark which is capable of detonating a hazardous atmosphere. That is why I was asking about the conduit or MC-HL cable. Our device (I.S. barrier) will clamp transient voltages, and limit the current so temperature limit, T4 is never exceeded by any device in our box or the wiring. The fuse we are using will be an IS safe fuse.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Since you are not attempting to qualify under Article 504, you do not have an intrinsically safe application. Under Section 501.135(B) you still have the problem of identifying your product/application for Division 2 since it will kick you back to Section 501.115(B).

While identified (as applied to equipment) [another Article 100 defined term] does not necessarily require listing or labeling, it can be a monumental task establishing its Suitability [see Section 500.8(A)] for Division 2. While you are at it read and absorb all of Section 500.8.
 

MWagner_MA

Member
Location
Hartford, CT
Terminology / Article 500

Terminology / Article 500

Got it. The terminology is taking some getting used to. Much of Article 500 is captured in UL 60079-0, and 60079-11 intrinsically safe systems which is what I have been diving into. Yes, it is some work, but what I'm using to when designing systems for Naval and Aerospace customers. Thanks for clarification on terminology and pointing to the paragraphs we need. We are doing a preliminary design review with our regulatory laboratory shortly to see how well our assumptions meet their requirements.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
If your current "regulatory laboratory" is an NRTL, you should have no problem.

BTW the UL 60069 series, while referenced heavily in Articles 505 and 506 for NEC Zone equipment, is not generally a recognized basis for equipment in NEC Divisions. They don't mix and match too well without an extremely knowledgeable designer.
 
BTW the UL 60069 series, while referenced heavily in Articles 505 and 506 for NEC Zone equipment, is not generally a recognized basis for equipment in NEC Divisions. They don't mix and match too well without an extremely knowledgeable designer.
UL 913 - for Division approval - actually refers almost exclusively to UL 60079-0 and UL 60079-11 requirements. Has done for several years now. So the OP should be OK using those.

(Side benefit, he should (mostly) get compatibility with Canadian, ATEX and IEC requirements at the same time.)

Other UL Division standards definitely don't play well with UL Zone standards. Or, at least, not yet.
 
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