You're right to be concerned and to insist on Code compliance, especially in hazardous locations. The "seen it, liked it, copy it" approach is dangerous and often leads to non-compliant and potentially unsafe installations.Here's a breakdown of the issues and potential solutions based on the NEC (National Electrical Code) and general best practices for Class I, Division 1 (CID1) locations

The Core Issue: Grounding and Bonding in Hazardous Locations

In CID1 areas, the goal is to prevent ignition by containing any potential sparks or arcs within explosion-proof enclosures. Proper grounding and bonding are crucial to achieve this. The main reasons for this are: Fault Current Path

A low-impedance ground path allows fault current to quickly return to the source, tripping the overcurrent protective device (OCPD) and de-energizing the circuit before a hazardous condition arises.

Static Electricity

In hazardous locations, static electricity can accumulate and discharge, creating a potential ignition source. Proper grounding helps dissipate this static charge.

Voltage Differences

Bonding reduces the potential for voltage differences between equipment, preventing sparks.

Analysis of Your Situation1. Cable Tray as Raceway

The NEC (specifically Article 392) does allow cable trays to be used as equipment grounding conductors (EGCs) if they meet specific construction and installation requirements. However, this is often misunderstood. Key considerations:

Listed Trays

The cable tray must be a listed cable tray specifically identified for grounding purposes. Most standard cable trays are not listed for grounding.

Sufficient Cross-Sectional Area

The tray must have sufficient cross-sectional area to safely carry the ground fault current. This is often difficult to determine without consulting the tray manufacturer's specifications and performing calculations.

Proper Bonding

The tray sections must be securely bonded together to ensure a continuous, low-impedance path. This typically involves bolting and the use of bonding jumpers at joints and splices.

Suitable Connections

Connections to the tray for grounding conductors must be suitable for the purpose (e.g., grounding lugs).

Assumptions: If the cable tray IS a suitable grounding raceway and is PROPERLY bonded, then while the cables are within the tray, the tray can serve as the EGC for the equipment connected to those cables. If the cable tray is NOT suitable as an EGC, then you must provide a separate, code-compliant EGC.2. The Problem at the Drop to the Device

This is the critical area. Once the cables leave the cable tray, they no longer benefit from the grounding properties of the tray (assuming it even has grounding properties). You need a continuous, dedicated EGC from the source (e.g., the panel supplying power to the instruments) to each individual device.3.

Instrumentation Cable with No EGC/Foil

This is the biggest hurdle. The fact that the instrumentation cable doesn't have a dedicated EGC or a foil shield suitable for use as one means you must provide a separate EGC.

Code References



NEC Article 250 (Grounding and Bonding)

This is the foundational article. Pay close attention to sections on equipment grounding, especially in hazardous locations.

NEC Article 500-505 (Hazardous Locations)

These articles provide specific requirements for CID1 locations, including grounding and bonding.

NEC Article 392 (Cable Trays)

If you're relying on the cable tray as an EGC, you must adhere to these requirements.

NEC Article 344 (Rigid Metal Conduit - RMC)

If you're using RMC as a wiring method in the hazardous location, you'll need to follow its installation and grounding requirements.

NEC Article 350 (Liquidtight Flexible Metal Conduit - LFMC)

If you're using LFMC, you'll need to follow its installation and grounding requirements.

Solutions

Here are several compliant options, ranked roughly from best to most complex/expensive:1. Re-evaluate Cable Selection

The best solution is to use instrumentation cable that includes a dedicated EGC meeting the requirements of the NEC. This is the simplest and most reliable long-term solution. Ensure the EGC is sized appropriately per NEC 250.122.
2.

Rigid Metal Conduit (RMC) or Intermediate Metal Conduit (IMC)

Run individual RMC or IMC conduits from the cable tray (properly bonded to the tray, assuming the tray can act as an EGC), to each instrument enclosure. The RMC/IMC itself serves as the EGC. Ensure the conduit connections are wrench-tight and use listed fittings suitable for hazardous locations. This offers excellent physical protection and a reliable grounding path. This may require explosion-proof sealing fittings.3.

Liquidtight Flexible Metal Conduit (LFMC) with Internal EGC

Run LFMC from the cable tray to each instrument enclosure. Crucially, pull a separate, properly sized EGC inside the LFMC along with the instrumentation cables. The LFMC itself is not considered an adequate EGC (NEC 350.60). Bond the EGC to both the cable tray (again, assuming it is a listed grounding tray) and the instrument enclosure. This provides flexibility for connections and vibration but requires the extra step of installing the EGC. Again, explosion-proof sealing fittings may be needed.4.

Install a Separate EGC Wire Alongside the Cable

This is a less desirable option but can be code-compliant if done carefully. Run a separate, appropriately sized EGC wire along with the instrumentation cable from the cable tray to each instrument. Secure the EGC to the cable at regular intervals using cable ties or other suitable methods. The EGC must be protected from physical damage. This option is typically only suitable for short runs in protected areas. This is the least physically protected of the options.

Important Considerations and Best Practices Explosion-Proof Enclosures

Ensure the instrument enclosures are truly rated for Class I, Division 1 environments and are properly installed. This includes using explosion-proof sealing fittings where required.

Sealing Fittings

Sealing fittings are essential to prevent the migration of flammable gases or vapors. They are required where the conduit enters the explosion-proof enclosure and may be required at other points in the conduit run depending on the specific installation. Follow the manufacturer's instructions for installing sealing fittings.

Bonding Jumpers

Use bonding jumpers to ensure continuity across all joints and connections in the grounding path. Use listed bonding jumpers designed for hazardous locations.

Documentation

Keep detailed documentation of the installation, including cable specifications, grounding conductor sizes, and bonding methods.

Qualified Personnel

Ensure the work is performed by qualified and experienced electricians who are familiar with hazardous location wiring practices. This is not a place for shortcuts or assumptions.

Local AHJ (Authority Having Jurisdiction)

Consult with your local electrical inspector or AHJ to ensure compliance with all applicable codes and regulations. They have the final say.

Grounding electrode conductor (GEC) & Bonding jumper: Ensure the cable tray is grounded back to the grounding electrode conductor, in accordance with NEC 250.

In Conclusion

You are right to question this "seen it, liked it" approach. There are no shortcuts to safety in hazardous locations. The absence of an EGC in the instrumentation cable is a significant problem that must* be addressed with a code-compliant solution. The solutions presented above provide a variety of ways to approach a compliant installation. The most prudent advice is to select instrumentation cable that includes an EGC as part of the cable. Flag for review