You are on the right track, but let's clarify some points for a complete understanding.

Your understanding is generally correct

NEC 2020 501.15(A)(1) Exception 4 does allow you to omit seals at conduit entries for devices that are part of a nonincendive circuit in Class I, Division 2 locations.

Key Considerations and Clarifications


Nonincendive Circuit Definition

This is the most critical part. A nonincendive circuit is one that, under normal operating conditions and abnormal conditions (such as short circuits, ground faults, etc.),

cannot produce a spark or thermal effect capable of igniting a specific hazardous atmosphere. This is achieved through careful design of the circuit's voltage, current, and components. Not Just Any Circuit

It's not simply a low-voltage circuit. It must be certified or demonstrated to be nonincendive for the specific hazardous atmosphere you are dealing with (e.g., methane, gasoline vapors, etc.).

The Murphy Centurion Panel

The crucial question is whether the

input circuit on the Murphy Centurion panel that you are connecting to is designed, tested, and certified as a nonincendive circuit for the hazardous location in question. You must confirm this in the panel's documentation (instruction manuals, certification documents, etc.). Look for markings or statements indicating compliance with a relevant standard (e.g., ISA/ANSI 12.12.01, IEC 60079-11 for intrinsic safety or a similar standard that addresses nonincendive circuits). If the documentation doesn't explicitly state that the input circuit is nonincendive, you cannot assume it is.2. Division 2 Location

This exception only applies to

Class I, Division 2 locations. In Class I, Division 1 locations, the requirements are more stringent, and nonincendive circuits are generally not sufficient to eliminate sealing requirements.3. Nonincendive Components

The switch itself (e.g., the level switch) connected to the nonincendive circuit must also be rated for the location. While it doesn't necessarily have to be explosion-proof, it must meet the general requirements for equipment in a Class I, Division 2 location. This typically means it should be enclosed in a suitable enclosure (NEMA 4, 4X, etc.) to protect it from the environment and prevent potential ignition sources (if any) from coming into contact with the hazardous atmosphere. The switch itself does not have to be "nonincendive" as it is part of a nonincendive circuit.4.

Wiring Methods

While you can omit seals at conduit entries to the nonincendive device enclosure, you still need to use appropriate wiring methods for the Class I, Division 2 location. This generally means using conduit (rigid metal or IMC) or approved cable types (e.g., TC-ER cable) with appropriate fittings. Surface run cable not in conduit would not be appropriate.5.

Documentation is Key! Have the documentation readily available for inspectors.

In Summary


Verify Nonincendive Certification

The most important step is to confirm that the input circuit on the Murphy Centurion panel is certified as a nonincendive circuit for the specific hazardous gases or vapors present in your location. Look for explicit statements in the panel's documentation.2.

Division 2 Application

This exception applies only to Class I, Division 2 locations.3.

Appropriate Wiring

Use proper wiring methods for Class I, Division 2 locations.4.

Suitable Enclosure

The level switch itself must be in a suitable enclosure rated for the environment.5.

Consult with Experts

If you are unsure about any aspect of this, consult with a qualified electrical engineer or a certified hazardous locations professional. Misapplication of these rules can have serious consequences.

Example

Let's say the Murphy Centurion panel's documentation states: "The discrete inputs are certified as nonincendive circuits per ISA/ANSI 12.12.01 for Class I, Division 2, Groups A, B, C, and D hazardous locations." If you are in a Class I, Division 2, Group C location (e.g., containing ethyl ether), you could likely use the nonincendive circuit exception and omit the conduit seal at the level switch enclosure, provided the level switch itself is in a suitable enclosure and the wiring method is appropriate. If you are in a Class I, Division 1 location, this exception would not apply.

If you cannot definitively prove that the input circuit is nonincendive, you must follow the standard sealing requirements for Class I, Division 2 locations. It's always better to err on the side of caution when dealing with hazardous locations. Flag for review