Mike Dolt Enterprises
Mike Dolt Enterprises
User: RFUSS, Location: USA
Asked on: Thursday, June 19, 2025 at 4:28 pm EDT
Answered on: Thursday, June 19, 2025 at 4:29 pm EDT
Question: I am part of a team developing an Ex ec process control instrument for Class I, Division 2 locations and we are at a design crossroads.I have reached out to some existing customers but I would love to get some feedback from industry professionals with installation experience.A goal is for the device to not require an enclosure. This limits the wiring methods the are approved under the NEC/CEC. We could connectorize the device with something like a rugged M12 or an M16. This would create a more compact and less expensive device, but we think it would lock end users into a limited number of cable vendors and cable types (These mostly come in ITC/PLTC cable types) and would make certain things like creating serial communication buses or power buses for multiple devices more difficult.Or we could create a terminal box that attaches to the top of the device with NPT or Metric porting that would allow users to connect armored cable, conduit, or anything else they can terminate to that box. This solution would be bulkier, more expensive and would require some additional electronics design work but it could be more flexible for end users.How do you feel about connectorized process instruments in hazloc? Would your facility be able to support both ideas? Would you prefer one solution over the other?
This is a great question and highlights a common trade-off in hazardous location instrument design. Here's my perspective as someone who's been in the trenches specifying, installing, and maintaining process instrumentation in hazardous locations for over 20 years
Understanding the Landscape:
Class I, Division 2
Remember that Division 2 inherently allows for the presence of flammable materials under abnormal conditions. This allows for some flexibility compared to Division 1.
User Preferences Vary Wildly
There is no one-size-fits-all answer. Some facilities are meticulous with standards, some are more pragmatic. You'll find strong opinions on both sides.
Cost is Always a Factor
Regardless of preference, everyone cares about the bottom line.
Analyzing Your Options
Connectorized Instrument (M12/M16)
Pros
Compact and Lower Cost
As you mentioned.
Faster Installation
Connectors significantly reduce wiring time.
Potential for Pre-tested Systems
If you offer pre-made cable assemblies, you can ensure quality and reduce field errors.
Cons
Limited Cable Choices
The ITC/PLTC restriction is significant. Many installations require armored cable for mechanical protection, especially in older facilities.
Single Point of Failure
A damaged connector or cable can take the entire device offline.
Vendor Lock-In Concerns
Users may feel forced to buy expensive or proprietary cables from limited sources. This is a major sticking point for many.
Bus Architectures
Building daisy-chained serial or power buses becomes more complex and might require custom solutions.
Future Expansion
Adding extra circuits later is difficult without replacing the entire cable.
Instrument with Terminal Box (NPT/Metric Ports)
Pros
Maximum Flexibility
Accepts a wide range of wiring methods (conduit, armored cable, etc.).
User Familiarity
Electricians and instrument technicians are very comfortable with this method.
Easier Bus Architectures
Simplifies power and communication bussing.
Future Expansion
Adding extra circuits is easier.
Cons
Bulkier and More Expensive
Increased size and component count.
Slower Installation
Wiring terminal blocks takes longer than plugging in a connector.
More Potential for Errors
More connections increase the risk of wiring errors.
Industry Professional Feedback and Recommendations
Here's what I'd tell you if I were a customer or installer:1.
My Preferred Approach (Generally)
The terminal box with NPT/Metric ports offers significantly more flexibility and is the preferred method. The biggest reason is field technicians know this method very well and there are a wider range of cable options. While the connectorized device is more economical and compact, the maintenance of these types of device in the field are almost always problematic. I have seen these used for simple discreet instruments with a very limited wiring scope but would hesitate to use them for a complex instrument like a process controller.2.
Support for Both Ideas
Yes, my facility could support both options, but it would depend heavily on the application. Consider these scenarios:
Connectorized
Ideal For
Simple, standalone instruments in controlled environments where ITC/PLTC cable is acceptable, and quick replacement is a priority. Maybe a pressure transmitter in a clean room setting.
Not Ideal For
Instruments requiring armored cable, those exposed to harsh environments, or those that need to be integrated into complex networks.
Terminal Box
Ideal For
Instruments that are critical to the process, require robust wiring, are part of a larger network, or may need to be modified or expanded in the future.
Almost Always Acceptable
It's a safe bet for most applications.3.
Specific Considerations and Design Suggestions
Hazardous Location Certification
Ensure both options are certified for Class I, Division 2. Don't cut corners here.
Connector Quality
If you go the connector route, use high-quality, ruggedized connectors that are specifically rated for hazardous locations and the expected environmental conditions. Consider connectors with robust locking mechanisms.
Terminal Box Material
Use a suitable material for the terminal box that resists corrosion and is compatible with the expected environment (stainless steel, fiberglass reinforced polyester, etc.).
Terminal Block Type
Use high-quality terminal blocks that are easy to wire and provide a secure connection. Spring-clamp terminals are generally preferred over screw terminals.
Cable Gland Selection
For the terminal box option, clearly specify the acceptable cable gland types and sizes to maintain the hazardous location rating.
Consider a Hybrid Approach
Think about offering a base model with a terminal box and an optional "connectorized" add-on module. This could cater to a broader range of customers.
Document Everything Clearly
Provide thorough documentation, including wiring diagrams, connector pinouts, and acceptable cable types for both options.
Survey More Customers
A broader survey of your target customer base is essential. Ask about their specific wiring requirements, preferred installation methods, and concerns about connectorized instruments.
Ease of Use
With any option, prioritize ease of use. Make sure the instrument is easy to install, configure, and maintain.4.
Important Questions to Ask Yourself
What are the typical wiring practices in my target industries? (e.g., Chemical, Oil & Gas, Pharmaceutical) What are the environmental conditions the instrument will be exposed to? (e.g., Temperature, humidity, chemicals, vibration) What level of technical expertise do my customers have? How important is ease of maintenance and repair? What is the expected lifespan of the instrument?In Summary:
While the connectorized approach can be appealing for its cost and size benefits, the terminal box solution offers greater flexibility, user familiarity, and long-term reliability, especially in challenging hazardous location environments. Thoroughly research your target market's needs and prioritize user experience and safety when making your final decision.Good luck! Let me know if you have any other questions. Flag for review