Let's break down the requirements for bonding in Class I hazardous locations when using explosion-proof flex conduit.

Understanding the Requirements Class I Locations

These are areas where flammable gases, vapors, or liquids are, or may be, present in the air in sufficient quantities to produce explosive or ignitable mixtures. Electrical equipment in these areas must be designed to prevent ignition of these substances.

Explosion-Proof Equipment

"Explosion-proof" doesn't mean the equipment prevents explosions. It means that if an explosion occurs inside the enclosure, it will contain the explosion and prevent it from igniting the surrounding atmosphere. It also means the enclosure's surface temperature won't get high enough to ignite the surrounding atmosphere.

Bonding (Grounding)

Bonding, also sometimes referred to as grounding, provides a low-impedance path for fault current to return to the source, facilitating the operation of overcurrent protection devices (circuit breakers or fuses). It's also crucial for minimizing touch potential, making equipment safer to handle. In hazardous locations, proper bonding is absolutely critical for two reasons:1. Fault Current Limitation:

You want to rapidly clear faults. High impedance paths can create sparks capable of igniting the atmosphere.2. Static Discharge

In some situations, static electricity can build up. A proper bonding system can help safely dissipate static charges.

Flex Conduit Considerations

Flexible metal conduit (FMC), including explosion-proof flex, is generally not considered an effective grounding path on its own. The connection points and the flex itself may not provide consistently low impedance.

The Answer to Your QuestionYes, you must run a bonding jumper (equipment grounding conductor) between the flex conduit connections in a Class I location. It is not ok to rely solely on the flex itself for the grounding path.

NEC Requirements (Relevant Sections)

While specific requirements depend on your jurisdiction and the exact installation, key sections of the National Electrical Code (NEC) related to this include: NEC 501.30(A) Grounding and Bonding

This is the core section for grounding and bonding in Class I locations. It typically requires equipment to be connected to an equipment grounding conductor sized according to NEC 250.122.

NEC 250.118 Types of Equipment Grounding Conductors

This section lists acceptable types of equipment grounding conductors. The equipment grounding conductor may be included within the same raceway or cable as the circuit conductors.

NEC 250.4(A)(5) Effective Ground-Fault Current Path

Ensures the grounding path has low impedance to facilitate the operation of overcurrent devices.

NEC 300.3(B)

All conductors of the same circuit, including the grounding conductor, must be run in the same raceway or cable.

Practical Implementation1. Internal or External Bonding Jumper

The bonding jumper can be run inside the flex conduit along with the circuit conductors, or it can be a separate conductor bonded to the outside of the flex connectors using appropriate grounding lugs.2.

Sizing

Size the bonding jumper according to NEC 250.122 based on the overcurrent protection device protecting the circuit.
3.

Material

The bonding jumper must be copper or another approved conductor material.4.

Terminations

Use appropriate listed connectors and fittings specifically designed for grounding in hazardous locations to ensure a secure, low-impedance connection.5.

Continuous Path

Ensure the bonding jumper provides a continuous, unbroken path from the motor back to the grounding bus in the panelboard or service equipment.

Important Considerations



Local Codes and Regulations

Always consult with local electrical codes and regulations, as they may have additional or more stringent requirements than the NEC.

Qualified Personnel

All electrical work in hazardous locations must be performed by qualified and experienced personnel who are familiar with the specific requirements for Class I locations.*

Inspection

Have the installation inspected by a qualified electrical inspector to ensure compliance with all applicable codes and regulations.

In summary, do not rely solely on the explosion-proof flex conduit itself for grounding. A properly sized and installed bonding jumper is essential to ensure a safe and compliant installation in a Class I hazardous location. Flag for review