Non-Incendive Devices in Hazardous Area, Powered from Safe Area

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muckleyd

Member
Location
longmont, co
Our design includes non-incendive lights and non-incendive push buttons located in a Class 1 Div 2 hazardous area that receives 24VDC from a I/O printed wiring board located in a safe area. The I/O printed wiring board receives 24VDC from a 20A Phoenix Power Supply also located in the safe area. The Power Supply and the I/O printed wiring board are both non-incendive rated (and could technically reside in a hazardous area).

Do we need to add resistors to our design in the safe area to limit the current of the discrete in/out, or is the idea that all the components in the design are non-incendive proof that the energy will not be enough to cause spark?
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Are you installing per a control drawing as required by Section 501.10(B)(3)? Odds are additional resistors won't be required, but it can't be said definitively from the information you supplied so far.
 

muckleyd

Member
Location
longmont, co
I apologize, I am a little new to this, but in regards to the control drawing, which component will we need to adhere to, the Power supply (in safe area), the I/O printed wiring board (in safe area), or the non-incendive light / pushbutton (in hazardous area)?

The ISA 12.12.01 defines the control drawing:

a drawing or other document provided by the manufacturer of the nonincendive field wiring apparatus or the associated nonincendive field wiring apparatus that details the allowed interconnections with other circuits or equipment . The control drawing includes the applicable electrical parameters to permit selection of equipment for interconnection.

Reading this it sounds like anything that interconnects with non-incendive wiring will need to adhere to the control drawing regardless of whether or not is in a safe or hazardous area.

For our I/O printed wiring board the cert information is the following:

Class 1,Div. 2, Groups A,B,C,D, T4
Class 1, Zone 2, AEx nA nC [nC] IIC T4, Ex nA nL [nL] IIC T4 Gc X
Ex ic nA [ic] IIC T4 Gc
Power Supply: 28 V dc, 0.81 A dc
Contact In: 0 to 32 V dc
Contact Out: 32 V dc, 3.15 A dc
Contact Wetting Out: 32 V dc, 110mA dc

To meet the rating of the label, does this mean we need to limit the current and/or voltage for non-incendive wiring going into the haz area?

The installation instructions are a little bit unclear and for our component it lists the electrical ratings (same as the above) and that it meets the ISA-12.12.01 2012 standard in hazardous and UL508 for non-hazardous. Are the electrical ratings what we need to ensure our parameters must meet or are they the ratings that device it connects to (light/push button) can not exceed (for example for a device in a haz location expected/rated to draw more power than the electrical ratings may not be used with this component.)




 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
At this point, I'd ask if you even have a manufacturer's control drawing. (BTW, it is also defined in the NEC in Section 500.2) So far, none of the equipment specifications you have cited indicate anything is actually nonincendive. None of the labeling on the I/O board indicates it is nonincendive; however, it appears to be suitable for Class I, Division 2. (Note: I'm certain it doesn't say Class 1 but rather Class I)

This doesn't necessarily mean the overall scheme isn't suitable for Class I, Division 2. In fact, if the lights and pushbuttons are listed for Class I, Division 2 (or 1) you are fine unless you are attempting to use an "unclassified location" wiring method which would require an IS or NI system.

Ever since the ISA glommed onto IS and NI systems, they have confused the issue no end.
 

muckleyd

Member
Location
longmont, co
OK- Did some digging and some research (mfg left off the control drawing)

This IO module in safe area is listed as a intrinsically safe/non-incendive apparatus thus making the Power supply in the safe area the associated apparatus (since it is maintaining the energy).

The entity parameter for the IO module has a very low Imax value of.132A which is a lot smaller than the Isc value of the Power supply. Is it possible to place resistors to limit the current to allow us to meet the Imax value of .132A?

If so, does the resistor need to be a "special" resistor, certified as a associated apparatus or could you use any old resistor?

Thanks
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Maybe we should clarify if "safe area" and "unclassified location" are synonymous in your mind. If they are, you don't need any resistor at all since the I/O board acts as a barrier to the system in the Division 2 location. If an internal I/O board fault occurred and it was transferred into the classified location then it certainly isn't intrinsically safe.

I'm still curious whether you are using a ?control drawing.
 
Additional Questions about powering devices form a safe area

Additional Questions about powering devices form a safe area

The system under development will utilize non-incendive rated, 24 VDC excitation, 4-20 ma signal, pressure transmitters located in a Class I, Div 2, Group B area. The 24 VDC excitation power and signal conditioner equipment will be located in a non-hazardous area. The signal conditioner equipment is rated as non-incendive. The question is related to the 24 VDC power supply requirements. Do non-incendive requirements mandate the use of separate current limited power supplies for each individual pressure transmitter, similar to commercially available multi-channel segment protectors or is the current rating of the connected non-incendive rated pressure transmitter, connected to a "standard" 24 VDC power supply using standard shielded instrumentation wire, assumed to be the energy limiting component to prevent generating sufficient energy to cause a problem in the hazardous area?
 

Smart $

Esteemed Member
Location
Ohio
What wiring method is being used in the Class I, Division 2 area?
Not sure if we have two posters (from different states) concerning the same or separate installations... or whether they understand what is meant by "wiring method"... which comes down to exposed cabling, or wire/cable in conduit.
 
Non-Incendive Pressure transmitter wiring

Non-Incendive Pressure transmitter wiring

Not sure if we have two posters (from different states) concerning the same or separate installations... or whether they understand what is meant by "wiring method"... which comes down to exposed cabling, or wire/cable in conduit.

This is a different installation from the one mentioned in the original post.
The wiring method proposed is to utilize PLCT wiring from a Class 2 rated power supply at 24 VDC and 4 amps to limit the delivered current to 100 watts max and a DAQ system, rated as non-incendive, also located in a safe area, to connect to non-incendive rated pressure transmitters in a Class I, Div 2, Group B area. The control drawing for the transmitter indicates no barriers required between the transmitter in the hazardous area and the DAC/power supply, but indicates wiring to be per the applicable NEC requirement.
 

Smart $

Esteemed Member
Location
Ohio
This is a different installation from the one mentioned in the original post.
The wiring method proposed is to utilize PLCT wiring from a Class 2 rated power supply at 24 VDC and 4 amps to limit the delivered current to 100 watts max and a DAQ system, rated as non-incendive, also located in a safe area, to connect to non-incendive rated pressure transmitters in a Class I, Div 2, Group B area. The control drawing for the transmitter indicates no barriers required between the transmitter in the hazardous area and the DAC/power supply, but indicates wiring to be per the applicable NEC requirement.
In CID2, that'd be 501.10(B)(3)...
(3) Nonincendive Field Wiring. Nonincendive field wiring
shall be permitted using any of the wiring methods permitted
for unclassified locations. Nonincendive field wiring systems
shall be installed in accordance with the control drawing(s).
Simple apparatus, not shown on the control drawing, shall be
permitted in a nonincendive field wiring circuit, provided the
simple apparatus does not interconnect the nonincendive field
wiring circuit to any other circuit.
Informational Note: Simple apparatus is defined in 504.2.​

Separate nonincendive field wiring circuits shall be installed
in accordance with one of the following:
(1) In separate cables
(2) In multiconductor cables where the conductors of each
circuit are within a grounded metal shield
(3) In multiconductor cables or in raceways, where the
conductors of each circuit have insulation with a minimum
thickness of 0.25 mm (0.01 in.)
 
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