Intrinsically Safe Marshalling Panels: Key Requirements for Zone 1 Instrumentation
Intrinsically safe (IS) marshalling panels play an important role in protecting instrumentation circuits operating in hazardous areas.
Although these panels are typically installed in safe areas, their design is critical to maintaining the intrinsic safety of electrical loops connected to Zone 1 instruments.
Incorrect barrier selection, poor wiring segregation or inadequate electrical protection can compromise the safety of an entire instrumentation loop.
BONNER recently designed and built an intrinsically safe marshalling panel for a pharmaceutical facility in Ireland. Here are five important considerations when designing and building safe-area interface panels for hazardous area instrumentation.
1. Understanding ATEX and Industry StandardsIntrinsically safe panel design must consider the relevant hazardous area regulations and engineering standards.
Key references include:
- Part 8 of the Safety, Health and Welfare at Work (General Application) Regulations 2007: Explosive atmosphere risk assessments and employer responsibilities.
- S.I. No. 230 of 2017 (ATEX): Requirements for equipment intended for potentially explosive atmospheres.
- IEC 60079-14: Design and installation of electrical systems in explosive atmospheres.
- IEC 60079-25: Requirements for intrinsically safe electrical systems.
- IEC 61439-1 and -2: Low-voltage electrical assembly design and verification.
Each standard addresses different aspects of safety, installation and panel construction.
2. Maintaining Segregation Between IS and Non-IS CircuitsPhysical separation between intrinsically safe and non-intrinsically safe wiring is essential.
If a 230 V AC supply or 24 V DC control conductor comes into contact with an IS circuit, the energy limitation protecting the hazardous area could be compromised.
Panel design must provide appropriate segregation between:
- Intrinsically safe instrumentation wiring.
- Low-voltage control circuits.
- Mains power distribution.
This includes separation within terminals, wiring ducts and cable routes. Where appropriate clearance cannot be maintained, suitable earthed metal partitions may be required.
Planning trunking routes and cable intersections during manufacture also makes future inspection and maintenance easier.
3. Identifying Intrinsically Safe CircuitsClear identification helps engineers safely inspect and maintain electrical panels.
Good practice includes:
- Using light blue terminals and trunking for IS circuits.
- Clearly labelling trunking containing intrinsically safe wiring.
- Identifying non-IS power circuits.
- Providing permanent barrier identification.
- Ensuring labels remain visible during maintenance.
These details are particularly important in complex pharmaceutical and process manufacturing environments.
4. Selecting the Correct Intrinsically Safe BarriersBarrier selection must be based on the electrical characteristics of the field instrument and its connecting cable.
Key parameters include voltage, current, power, capacitance and inductance.
The barrier’s output parameters must remain within the permitted input limits of the field device, while cable capacitance and inductance must also be considered. Gas group and temperature classification must suit the hazardous area.
These calculations should be documented for every loop in accordance with IEC 60079-25.
BONNER uses galvanically isolated barriers where appropriate, avoiding the requirement for a dedicated high-integrity IS earth associated with Zener barriers.
Control system compatibility, fuse selection, spare channels and isolator positioning should also be confirmed during the design stage.
5. IEC 61439 Verification and Factory Acceptance TestingIntrinsically safe marshalling panels are also low-voltage electrical assemblies and must meet applicable IEC 61439 design and verification requirements.This includes consideration of:
- Temperature rise and thermal management.
- Dielectric properties.
- Short-circuit withstand.
- Electrical clearances and creepage distances.
- Protective circuit continuity.
Before delivery, routine verification and Factory Acceptance Testing (FAT) should confirm that the panel meets its design and client specifications. A typical handover package includes electrical drawings, I/O schedules, barrier calculations, verification records, FAT results and applicable declarations of conformity.
Identifying and resolving deviations in the workshop helps minimise commissioning delays and modifications on site.
Intrinsically Safe Panel Design with BONNERDesigning an intrinsically safe marshalling panel requires expertise in hazardous area requirements, instrumentation, electrical segregation and industrial automation.
BONNER works with pharmaceutical and process manufacturing clients to design and build industrial control and instrumentation panels that integrate with existing plant infrastructure.
From barrier selection and panel design to electrical assembly, FAT and supporting documentation, we deliver practical engineering solutions for demanding industrial environments.
Planning an intrinsically safe panel or hazardous area instrumentation project? Contact the BONNER team at www.bonner.ie to discuss your requirements.