New requirements for intrinsically safe circuits in hazardous locations
February 11, 2019 - One of the important changes introduced by the 2018 CE Code, with regard to the treatment of designated hazardous locations, is how the code addresses the use of ‘intrinsically safe’ (IS) field wiring circuits, which are designed to limit electrical energy levels to prevent ignition of the explosive atmosphere—i.e. gas or dust—surrounding the equipment.
While previous editions of the code incorporated limited requirements for the installation of IS equipment, the latest revisions have aimed to align its rules with those of the International Electrotechnical Commission (IEC) and the National Electrical Code (NEC).
“You can’t evaluate the safety of a circuit unless it is properly documented,” says Allan Bozek, a professional engineer and hazardous locations specialist with Calgary-based EngWorks. “In the past, the CE Code made no mention of the need to document an IS design, so little attention was paid to it. This made it impossible for electricians and inspectors to know if an circuit was safe after installation, as the safety of the design would depend on the proper selection and integration of circuit components.”
Bozek was among those who helped update the CE Code accordingly, which included creating a new version of Appendix F.
“Appendix F has been rewritten to provide guidance on preparing engineering documentation of IS and non-incendive (NI) circuits,” he explains. “The documentation needs to define the entity parameters for the devices in a hazardous location, the barriers in a safe location and the wiring parameters associated with the circuit. The entity and wiring parameters are then resolved to keep the energy levels in the circuit below the ignition thresholds.”
Circuits can still be designed the same as in the past. What’s new is the insistence on documentation, so as to verify their safety.
Specifically, under Rule 18-064, the 2018 CE Code states (a) where an IS electrical system or NI field wiring circuit is installed in a hazardous location, a descriptive systems document (DSD) shall be provided, and (b) IS electrical systems and NI field wiring circuits shall be installed in accordance with the DSD.
As Bozek puts it, the intent is to provide sufficient information to qualified professionals for the installation, verification and maintenance of these circuits.
Rule 18-064 also requires any insulated conductors of IS or NI field writing circuits and those of other circuits to be separated within any raceway, compartment, enclosure, outlet, junction box or similar fitting (other than a cable tray) by no less than 50 mm, a grounded metal barrier no less than 1.34 mm (No. 16 MSG) thick or a non-metallic insulating material no less than 1.5 mm thick. Armoured cable assemblies also meet the separation requirements.
“The intent here is to prevent IS circuits from being cross-wired or energized under fault conditions by adjacent non-IS wiring circuits,” says Bozek.
The appropriately insulated conductors of different IS or NI circuits, however, are permitted within the same raceway, compartment, outlet, junction box or multi-conductor cable.
Finally, the rule requires IS and NI system components and wiring to be properly indicated as such. This includes identification at terminal and junction locations, along with permanently affixed labels or light blue colour coding (where no cables or insulated conductors of the same colour are used) to identify wiring methods.
In Appendix F, which is informative but non-mandatory, while guidance is offered in preparing engineering documentation, the design of IS and NI circuits has been removed. Instead, design references are listed.
This is based on an acknowledgment that IS technology is in a constant state of further development and, as such, a designer must always refer to the latest standards to ensure the implementation of a safe design.
At the same time, Appendix F states where an engineer is involved, the DSD should be authenticated under professional seal documentation and records. Both the DSD and its supporting calculations should be kept on file by the facility’s owner and/or operator for the life of that facility, with a management-of-change process in place to ensure the DSD remains valid throughout that life.
The documentation must include a block diagram of the system, listing all of the items within it, including simple apparatus and interconnecting wiring, along with a statement of the group subdivision. It must also indicate the level of protection for each part, the temperature class or maximum surface temperature of the equipment and the ambient temperature range (if the components are subject to temperatures lower than -20 C or higher than 40 C).
Further requirements include, where applicable, the electrical (entity) parameters of all IS and associated apparatus and interconnecting wiring, evaluation thereof for a safe installation, identification of simple devices throughout the circuit, details of grounding and bonding requirements and reference to manufacturers’ control drawings.
“A DSD may also be in the form of a data sheet covering multiple devices of a similar design,” Bozek explains.
The main reasons for the changes, as Bozek puts it, are both to ensure safety and to harmonize Canada’s requirements with those defined in the aforementioned IEC and NEC standards.
“These changes are important because we’ve seen a lot of misunderstandings of the rules,” says George Morlidge, retired chief electrical engineer for Fluor Canada. “Previously, I haven’t been a big supporter of the IS idea because, too many times, people thought they didn’t have to follow the other rules of the code.”
As Morlidge puts it, in the past, entire manufacturing plants were IS. Yet at the same time, some important circuits could not be defined as IS. This led to a mixture of IS and non-IS circuits.
Further, many hazardous locations previously called Zone 1 are now defined as Zone 2, for which suitable equipment is available without it having to be IS.
“We’re now at the point where about 95% of plants are Zone 2 and we’re not seeing whole plants go IS anymore,” says Morlidge. “There’s a significant cost to IS equipment, but we can save money in Zone 2 conditions. There’s very little Zone 1 left and only a few Zone 0 one-offs. Allan did a good job at the code update. This status quo is about right.”
This article originally appeared in the February 2019 issue of Electrical Business magazine.
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