Remote IO Cabinets versus Junction Boxes in Industrial Control Systems

 

 

 

Contributed by Justin Grubbs, P.E. – I&E Department Manager

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Remote IO Cabinets versus Junction Boxes in Industrial Control Systems

With the modern advances in control systems architecture and communications protocols, the technology available to us today is leaps and bounds above what it was in the era of relay and timer logic as well as the first few generations of Programmable Logic Controllers (PLC). Given the tools available to us today, isn’t it time we realign our thinking when it comes to the practical implementation of control systems? The days where we were required to house all of the control systems hardware components in a centralized location are no more. Improvements in the efficiency, reliability, redundancy, and cost of networking components have allowed us the opportunity to provide a more robust, expandable, and cost-effective design.

In earlier iterations of industrial control system solutions, the flexibility of the installation was limited by the type of communications used. In most cases, these used a type of serial communications which is extremely limited in speed and distance in comparison to the modern-day performance of PLCs. With the ever-growing rates of data transfer and speeds at which the data is needed diminishing, the only way for continued growth is to advance to faster, more efficient communications protocols such as Ethernet/IP. Imagine attempting to pull up real-time data on a turbine running at 10,000+ RPM on an RS-232 serial communications interface, or to put it in modern terms, attempting to watch your favorite cat video on the internet via a dial-up internet connection. In one case, you’ll have to wait a very long time to see the cat; in the other case, there could be a catastrophic failure on the order of millions of dollars due to the latency in response time. However, with the speeds and distances which are achievable with modern copper and fiber Ethernet communications, limitations for where PLC hardware is located is no longer an issue.

In a traditional PLC design, a typical implementation for a large industrial facility was to have several locations (junction boxes) scattered throughout the facility where field instrumentation would be wired via individual cables. These junction boxes serve as a splice point to allow for larger multi-pair or multi-conductor (home run) cables to connect back to the central control system cabinet which held the marshaling terminals and PLC hardware. With this method, each cable running to an end device had at least 4 terminations (at the PLC, at the home run side of the junction box, at the field side of the junction box, and at the end device). This means that there are at least two added points of failure or potential for error for every single conductor. With almost any modern PLC, we can now locate IO modules remotely in the field (remote IO or RIO cabinets). Rather than having multiple single points of failure in each cable, we can build redundancy in the communications architecture of the PLC system and almost entirely remove a potential for having a single point of failure. As one can see in figures 1 and 2 below, the traditional junction box design has twice the number of terminations as a RIO cabinet design. Additionally, if any one of the blue cables were cut, there would be a failure on multiple instruments. With a RIO cabinet design, if any of the red cables were to be cut, there is no loss in data as this is a redundant ring type of network. From an expandability standpoint, when a traditional junction box design requires expansion, multiple large cables must be run at potentially long distances to connect the new field IO to the main PLC. In order to bring field IO to the main PLC with a RIO cabinet design, all that need be run is two small communications cables regardless of the size of the expansion.

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As with most design implementations, an ever-present determining factor is cost. On the surface, it may seem that a RIO cabinet design is more costly due the additional networking components required. It is true that additional Ethernet and fiber cards, patch panels, and switches are needed; however once construction is factored in, the overall cost is much less. In the above example figures, the cost of the PLC hardware is very similar, the only significant cost differences being additional communications cards and power supplies. The enclosures required for the RIO cabinets are larger than traditional junction boxes and also typically must be purged with dry air or nitrogen if located in a hazardous (electrically classified) location. When comparing the cost of only the PLC hardware, enclosures, and communications components, the cost for the RIO cabinets will be roughly 10% more depending on the size of the implementation. When comparing the cost of the cabling, conduit, cable tray, bulk construction materials, and labor, there is a cost savings with a RIO implementation on the order of 30-50%. One can see this when comparing the size and magnitude of terminations and cables between Figures 1 and 2 (red versus blue cables). In a junction box implementation, there is a minimum of 4 additional terminations per IO. This cost is magnified when considering all of the additional cabling and raceways it takes to wire between the junction boxes and PLC cabinet. All of these factors result in additional field labor and consumable construction materials.

When comparing all factors of a traditional implementation with a RIO cabinet implementation, there really is no comparison. With the speeds and fault-tolerant construction of modern networking components, the drawbacks of relying on a network are all but gone. The expandability of a networked control system is very flexible and nearly limitless without the worry of needing excessive raceway space. Add these factors to the fact that the total installed cost of a RIO system is much less than that of a junction box design and it is hard to argue why one wouldn’t choose a RIO system.

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Justin Grubbs H+M Industrial EPC

Justin Grubbs, P.E. – I&E Department Manager at H+M Industrial EPC

B.S. in Electrical Engineering

Justin has +8 years of industrial engineering, construction, and commissioning experience. He has experience with design, engineering, and construction including but not limited to: leading I&E construction, developing plant control documents, directing control systems programming personnel, performing factory and site acceptance testing of electrical/process analyzation/control systems equipment, designing power distribution and motor starting systems, stamping and submitting electrical permitting packages, directing commissioning efforts, developing instrumentation specifications, validating engineering data, specifying I&E material, and training operations personnel. With previous EPC experience from Optimized Process Designs, LLC – a subsidiary of Koch Chemical Technology Group – Justin joined H&M in 2014 to lead the I&E department.

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Advantages of LED Lighting in Industrial and Hazardous Environments

 

 

Contributed by Justin Grubbs, P.E. – I&E Department Manager

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Advantages of LED Lighting in Industrial and Hazardous Environments

Advantages of LED Lighting in Industrial and Hazardous Environments

Technology continues to develop and improve in the electronics industry. Solid state electronics continually become more and more energy efficient, smaller in size, and more cost effective to manufacture. The advancements made in this field translate to a wide variety of electrical components. One of these is energy-efficient lighting such as light emitting diode (LED) luminaires. LED lighting has a great number of benefits over traditional High-intensity Discharge (HID) lighting such as Metal Halide or High Pressure Sodium lamps, the main benefits being a large increase in energy efficiency and the life of the lamp.

In an industrial hazardous environment, there can be a large amount of time spent to change a bulb in a traditional HID luminaire. The amount of time spent by maintenance personnel to acquire the correct replacement bulb, fill out hot work permits, job hazard analysis, execute lock out tag out procedures, locate equipment needed such as a man lift, and physically change the bulb adds up over the life of the fixture. This is a very important task as lack of sufficient lighting is a safety concern and can lead to a hazardous condition. For a traditional Metal Halide lamp operated for 12 hours a day, the bulb will need to be replaced an average of every 2.5 years. LED lighting is rated to maintain an acceptable light output for 13.7 years when operated 12 hours a day at an ambient temperature of 131°F, this goes up to 45.7 years at an ambient temperature of 77°F.

The initial cost investment of LED luminaires is approximately 35-40% more, however they consume approximately 20% less energy than a comparable HID luminaire. Additionally, the cost of other materials for the installation of an LED lighting system is much less than that of an HID system. Since the load of LED luminaires is less than HID luminaires, there are fewer feeder breakers needed, fewer lighting contactors needed, and smaller cable can be used which translates to taking up less space in cable trays and using smaller conduit and fittings.

As an example installation, take a project needing a relatively small area of illumination such as a barge/ship dock which is classified as an NEC Class 1, Division 2, group C&D area. Assume that a quantity of 30 Metal Halide HID flood light luminaires rated at 250W are sufficient for the lighting requirements of this area. Comparably, a quantity of 30 LED luminaires rated at 149W will also be sufficient for the lighting needed. The given cost variables are as follows:

  • Cost of LED luminaire is 38% more than HID
  • Maintenance time to change 1 bulb is 4 man-hours total (including permitting and LOTO) at a rate of $60/hour
  • The lighting operates 12 hours a day
  • Replacement HID lamps are $12
  • Energy cost is $0.06/kWhr

The annual energy savings with LED luminaires will be just under $1,100, the annual lamp and maintenance savings will be $3,000. The additional initial investment of the LED luminaires over the HID version will be returned in energy and maintenance savings after 1.5 years. The LED fixtures will completely pay for themselves after 5.3 years, and are rated to continue to operate for another 8.4 years before needing maintenance (in modern fixtures, changing an LED cluster is the same amount of man-hours as changing a traditional bulb). This is for a worst case constant ambient temperature of 131°F; for an ambient temperature of 77°F, it will be 40.4 years after the LEDs have completely paid for themselves before maintenance is needed.

The above example does not take into account the cost reduction in materials needed for installation of the LED luminaires. In this project example, if the luminaires are installed on a 120V system, 4 circuits would be needed for the HID version, whereas only 2 circuits would be needed for the LED version. This results in less breakers purchased, smaller wire/conduit/cable tray needed, less photocells, and fewer lighting contactor circuits. All of these will result in reduced construction labor and material costs.

To summarize, the technology of hazardous area LED luminaires has come a long way since their inception. They continue to become lower in cost, increasingly more energy efficient, and have various configurations of lighting clusters so that the distribution of light can vary from a large oval shape, to a long narrow beam, or an intense spot light. LEDs can also be specified as being a full spectrum cool white or warm white, rather than the light spectrum limitations of Metal Halide and High Pressure Sodium HID lighting. Though the initial investment of LED luminaires is more than comparable HID lighting, an LED installation will have a long-term significant cost savings over HID.

References:

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Justin Grubbs H+M Industrial EPC

Justin Grubbs, P.E. – I&E Department Manager at H+M Industrial EPC

B.S. in Electrical Engineering

Justin has more than 7 years of industrial engineering, construction and commissioning experience. He has experience with designing, engineering, leading I&E construction, developing plant control documents, directing commissioning efforts, overseeing instrumentation specifications, validating engineering data, specifying I&E material and training operations personnel.

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Prevent Nuisance Tripping – Proper Conductor Sizing Techniques per 2014 National Electrical Code

 

 

Contributed by Justin Grubbs, P.E. – I&E Department Manager

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Prevent Nuisance Tripping – Proper Conductor Sizing Techniques per 2014 National Electrical Code

Prevent Nuisance Tripping - Proper Conductor Sizing Techniques per 2014 National Electrical Code - H+M Industrial EPC

I have gone skydiving more than a few times in my life. As an active and licensed skydiver, the safety requirements involved are clear and have been established as the cornerstone of the sport. The requirements range from medical considerations to equipment specs, each one extensively thought through and put in place to ensure safety from the time you put on your rig to the time you land under your parachute. Coincidentally, these type of regulations are also common in my line of work. Just like with skydiving, the techniques used when sizing conductors for electrical projects are imperative to the process. You wouldn’t jump out of an airplane with the wrong parachute, so why design electrical systems with incorrectly sized conductors?

Throughout my experience working in the oil, gas, and petrochemical processing industry, I have seen numerous instances of errors committed while sizing conductors and performing voltage drop calculations per the National Electrical Code® (NFPA 70 – NEC). These errors can have a wide variety of effects which range from causing equipment to operate incorrectly or inefficiently to potentially causing serious injury or death to personnel. There are many factors and considerations which must be taken into account when performing these calculations.

For the purposes of this article, assume that we are sizing a conductor which meets the requirements of Table 310.15(B)(16) (formerly Table 310.16) of the 2014 National Electrical Code. Furthermore, assume that a THHN copper conductor will be used. The first consideration one must make when determining the appropriate conductor size is the temperature rating of the conductor. In this application, a 90°C rated conductor is being used. Does this mean one should use the ampacity listed in the 90°C column of this table? Perhaps surprisingly, no, it does not. Remember that the temperature rating in this table also applies to termination points of the conductor as these will be operating at the same temperature as the conductor itself, see 310.15(A)(B) and 110.14(C). In my experience, the most common rating for a low voltage breaker terminal is 75°C. According to an Eaton® (who also manufactures breakers for Rockwell Automation®) Application Paper, the terminals on molded-case circuit breakers are rated for a maximum temperature of 75°C. With this information, the correct column to use for conductor ampacity rating is the 75°C column.

Table 310.15(B)(16) provides a starting point for sizing a conductor. This table makes a number of assumptions, the most notable of which is that the conductor is installed in an environment with an ambient temperature of 30°C (86°F). Most applications in my experience have exceeded this ambient temperature requirement (especially when installed in Texas) and have therefore required an adjustment factor to be used. Table 310.15(B)(2) contains these adjustment factors.

Voltage drop is referenced in a number of places in the NEC as an Informational Note. Section 210.19(A) IN No. 4 is the first reference to voltage drop in the code. The significance of this is that Informational Notes as defined in the NEC are NOT code requirements. These are intended to provide recommendations for best engineering practices and not enforceable as a requirement of NEC, see 90.5(C). This being said, the NEC is intended to be a minimum requirement for electrical installations. It is published by the National Fire Protection Association as a means to mitigate harm to personnel or property. In most cases, good engineering practices, industry standards, and client specifications have requirements which are above and beyond NEC; voltage drop is by far the most common example of this. Consider a 3-phase 480V MCC lineup which is fed from any number of upstream transformers and switchgear. According to NEC, the total voltage drop of all feeder and load conductors to a connected load should be no more than 5% voltage drop for reasonable efficiency of operation. If this MCC were connected to a load which contained protective relaying, even this level of voltage drop may cause nuisance tripping. Additionally, if the voltage drop is too great at the load terminals, the increase in the current passing through the load conductors may cause upstream overcurrent protective devices to trip.

Whether it is skydiving or conductor sizing, it is important not to jump into (or out of) something without understanding all necessary factors. These factors are vital to safe and reliable operational decisions. The potential issues that stem from improperly sizing conductors vary in severity but are all important nonetheless. Always make sure to double check codes, applicable specifications, and industry recommendations to help decrease the likelihood of issues that could arise.

 

References: 2014 National Electrical Code® published by the National Fire Protection Association®, Eaton® Application Paper AP01200004E

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Justin Grubbs H+M Industrial EPC

Justin Grubbs, P.E. – I&E Department Manager at H+M Industrial EPC

B.S. in Electrical Engineering

Justin has more than 7 years of industrial engineering, construction and commissioning experience. He has experience with designing, engineering, leading I&E construction, developing plant control documents, directing commissioning efforts, overseeing instrumentation specifications, validating engineering data, specifying I&E material and training operations personnel.

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