Okay, this is a common challenge when dealing with hazardous location installations. You're right; manufacturers often don't provide clear-cut "seal required" or "seal not required" statements, leaving it up to the engineer or electrician to interpret the code. Here's a breakdown of what needs a seal fitting in Class I, Division 1 and 2 areas, and how to approach those tricky electronic devices, based on the NEC (National Electrical Code, specifically Article 501), as well as some practical considerations

Understanding the Fundamentals
Purpose of Seals

Seal fittings are primarily designed to:

Prevent the passage of flammable gases, vapors, or dusts from one portion of the electrical system to another through the conduit. This is especially crucial in Division 1 areas, where ignitable concentrations are normally present. Limit the explosion pressure that can build up inside the conduit system and prevent it from propagating to other equipment. Key Code Sections (NEC)



501.15 (Sealing and Drainage)

This is the section you need to study carefully. It outlines the specific requirements for seal fittings in Class I, Division 1 and 2 locations.

General Rules of Thumb Division 1

More stringent requirements. Assume you need a seal unless you can explicitly prove otherwise.

Division 2

Less stringent, but still requires careful evaluation. Seals are required where the potential for gas/vapor migration is present.

Explosionproof Enclosures

If a device is in an explosionproof enclosure and the conduit run enters that enclosure, you generally need a seal fitting close to the enclosure (within 18 inches for Division 1).

Intrinsically Safe (IS) Systems

Intrinsically Safe systems have specific sealing requirements outlined in Article 504 of the NEC. Follow manufacturer guidelines and the requirements of 504.40.

Dust-Ignitionproof Enclosures (Class II)

If applicable, seals are required to prevent dust propagation.

Specific Devices and Scenarios (Focusing on Your Question)

Here's how to approach the types of devices you mentioned:1. Transmitters (Pressure, Temperature, Level, Flow)



Division 1



If the transmitter is in an explosionproof enclosure and connected to a conduit system

Seal within 18 inches of the enclosure (501.15(A)(1)). The seal must be rated for Class I locations.

If the transmitter is Intrinsic Safe, consult Article 504 of the NEC. An intrinsically safe barrier is required to protect the IS circuit. If the transmitter is installed in a flameproof enclosure

Same as explosion proof.

Division 2



General Rule

A seal fitting is required where the conduit enters an enclosure that is required to be explosionproof, dust-ignitionproof, or purged and pressurized.

If the transmitter enclosure is not required to be explosionproof

You may not need a seal if the conduit system is unlikely to transmit flammable gases or vapors. This is a judgment call based on the environment and potential for leakage. If there is any doubt, install a seal.

If the conduit run is long and goes to a non-hazardous area

You may not need a seal at the transmitter enclosure. However, you will need a seal where the conduit leaves the hazardous area and enters the non-hazardous area (501.15(B)(2)).

If the transmitter is Intrinsic Safe, consult Article 504 of the NEC. An intrinsically safe barrier is required to protect the IS circuit.2. Sensors (Proximity, Photoelectric, etc.)



Division 1

Same rules as transmitters apply. Evaluate the enclosure type (explosionproof, IS, etc.) and follow the corresponding NEC requirements.

Division 2

Same rules as transmitters apply. Assess the enclosure type, conduit run, and potential for gas/vapor transmission.3.

Control Valves (Solenoid Valves, Actuators with Position Feedback)



Division 1



Solenoid Valves

These are often inherently spark-producing, so they are almost always in explosionproof enclosures and require a seal fitting within 18 inches.

Actuators with Position Feedback

Same as transmitters. Evaluate the enclosure type and follow the corresponding NEC requirements.

If Intrinsic Safe, consult Article 504 of the NEC. Division 2



Solenoid Valves

If in an explosionproof enclosure, seal required. If not explosionproof (e.g., general-purpose enclosure), seal may be required depending on the environment and potential for gas migration. Err on the side of caution and install a seal.

Actuators with Position Feedback

Same as transmitters. Assess the enclosure type, conduit run, and potential for gas/vapor transmission.

If Intrinsic Safe, consult Article 504 of the NEC.4. Electronic Devices Without Explicit Explosionproof Enclosures



Division 1

Almost certainly require explosionproof enclosures and seals. If the manufacturer is providing a device that's intended for Division 1 without an explosionproof enclosure, that is a major red flag. You'd need to use an enclosure from another manufacturer or look at alternative technologies (IS).

Division 2

This is where it gets the most nuanced.

Sealed Devices

Look carefully at the device's markings and documentation. Some devices are specifically designed and certified as "non-incendive" or "suitable for Division 2" without requiring an explosionproof enclosure. These may not require seals, but the manufacturer's instructions must be followed precisely.

Enclosure Requirements

If there are no special certifications, you may need to provide your own explosionproof enclosure.

Consider Purging/Pressurization

For some devices, you could consider using a purged and pressurized enclosure (NEC Article 505) as an alternative to explosionproof. However, this adds complexity and requires ongoing maintenance.

Key Considerations and Best Practices



Documentation is Critical

Keep thorough records of all equipment, hazardous area classifications, and your justification for sealing decisions.

Consult with a Qualified Professional

If you're unsure, consult with a qualified electrical engineer or certified hazardous locations inspector.

Err on the Side of Safety

If in doubt, install a seal. It's far better to spend a little extra money on a seal than to risk a potential explosion.

Manufacturer Data Sheets

Even if the data sheet doesn't explicitly say "seal required," look for clues. Does it mention an explosionproof enclosure? Does it state "suitable for Division 2" with any caveats?

Control Drawings

For Intrinsically Safe systems, the control drawing is a required document.

Consider Conduit Fill

When installing seals, remember that the fill requirements for the conduit do not apply in seal fittings.

Seal Location

Seals should be accessible for inspection and maintenance.

Use the Right Sealant

Use the sealant recommended by the seal fitting manufacturer.

Where to Look for More Information



NEC (National Electrical Code)

Articles 500, 501, 504, 505, and related sections.

NFPA 496 (Purged and Pressurized Enclosures)

If you consider purging/pressurization.

ISA (International Society of Automation)

ISA has standards and training related to hazardous locations.

UL (Underwriters Laboratories)

UL provides certifications and standards for hazardous location equipment.

Local Electrical Codes and Regulations

Make sure you comply with all local requirements.

Example Scenario

Let's say you have a pressure transmitter in a Class I, Division 2 area. The manufacturer's data sheet says the transmitter is "suitable for Class I, Division 2 when installed in accordance with manufacturer's instructions." The instructions don't mention a specific enclosure type, but the device is small and uses very low power. The conduit run is short and goes to a control panel in a non-hazardous area.In this case, you might be able to justify not* using a seal at the transmitter enclosure. Your reasoning would be:1. The manufacturer has certified the device for Division 2.
2. The conduit run is short, minimizing the potential for gas migration.3. The other end of the conduit run is in a non-hazardous area.
4. Install a seal at the transition from hazardous to non-hazardous location.However, you would need to carefully document this decision and be prepared to justify it to an inspector. If there were any doubts about potential gas leakage, you should install a seal.

In conclusion, determining whether or not to install a seal fitting on a device depends on many factors. Always refer to the NEC code, documentation, and the environment the device will be installed in. Flag for review