5.2 Bonding Raceways, Enclosures & Equipment

5.2 Bonding Raceways, Enclosures & Equipment

Quick Answer: Bonding ties metal raceways, enclosures, and equipment together into one electrically continuous fault path. Grounding ties that path (or the system) to earth where Article 250 requires it. On load-side equipment, bonding jumpers usually track Table 250.122. On the supply side of the service disconnect (and certain SDS supply-side connections), bonding jumper sizing follows 250.102(C)—closer in spirit to service conductor sizing than to ordinary EGC tables.

This section is the “continuity” half of Prov’s Grounding and Bonding outline. Sizing an EGC correctly is useless if a painted fitting, concentric knockout, or flexible connector breaks the metal path. Arkansas Journeyman items often ask what must be bonded, which jumper size, or whether a method provides an effective ground-fault current path.

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Bonding vs grounding (exam-grade distinction)

If metal parts are bonded but the system is not grounded where required, you can still have a dangerous installation. If parts are “grounded” to earth but not bonded to each other, fault current may not return to trip the breaker. Prov loves stems that swap these words—read carefully.

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General bonding requirement (250.90 and neighbors)

250.90 requires bonding where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and similar metal parts that are to serve as grounding conductors or that require grounding must be bonded where necessary to ensure that path.

Practical translation for the exam:

1. Every metal enclosure and raceway in the equipment grounding path must remain electrically continuous.
2. Where continuity would be questionable (loose joints, reducing washers, concentric knockouts, flexible connections), install a bonding jumper or listed bonding fitting.
3. Bonding jumpers must be connected with methods that ensure lasting continuity—listed pressure connectors, terminal bars, exothermic welds, and other Code-recognized methods under 250.8 / bonding sections—not sheet-metal screws alone where prohibited.

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Raceways and enclosures — where bonding shows up

Metal raceways as the path

When RMC, IMC, EMT, or other 250.118 methods serve as the EGC, fittings must be made up wrench-tight and remain continuous. Flexible metal conduit and liquidtight flexible metal conduit have length and qualification limits when used as the EGC—open 250.118 rather than assuming every FMC whip is an EGC.

Bonding around impaired connections

Classic problem spots:

• Concentric or eccentric knockouts on enclosures—especially on the supply side of service equipment—often require bonding bushings or bonding jumpers because the remaining metal ring may not provide a reliable path.
• Reducing washers and similar fittings can impair continuity; bond around them when required.
• Expansion fittings / telescoping sections may need an external bonding jumper sized per the applicable bonding section.
• Receptacle yokes and equipment grounding terminals must maintain continuity to the box where the Code requires box grounding continuity.

Enclosures and equipment frames

Bond metal enclosures to the equipment grounding conductor. Panelboards, disconnects, motor controllers, and utilization equipment frames that require grounding must be connected to the EGC so a fault to the case becomes a low-impedance short that clears the OCPD.

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Bonding jumper types and sizing (250.102)

250.102 is the sizing home for bonding jumpers and bonding conductors. Separate supply-side from load-side mentally:

Load-side equipment bonding jumpers

On the load side of the service overcurrent device (and similarly for feeders/branch circuits), equipment bonding jumpers are generally sized from Table 250.122 based on the overcurrent device protecting the circuit conductors—same table family as EGCs. That is why a bonding jumper around a load-side concentric knockout on a 100 A feeder often lands on 8 AWG copper when a wire-type jumper is used (confirm in table).

Supply-side bonding jumpers — 250.102(C)

On the supply side of the service disconnecting means (and for certain separately derived system supply-side connections), bonding jumpers are sized from 250.102(C) using the size of the ungrounded supply conductors—commonly via Table 250.102(C)(1) (related historically to the 250.66 philosophy). These jumpers can be larger than a casual Table 250.122 guess because they sit ahead of the service OCPD in the fault path logic.

Exam habit: If the stem says “supply side of the service,” “service bonding jumper,” or “main bonding jumper,” do not blindly open only Table 250.122. Open 250.24 / 250.28 / 250.102(C) as the stem directs. Main bonding jumper rules from Chapter 4 remain in play for service equipment; this section’s load-side raceway/enclosure bonding is the everyday continuity work downstream.

Parallel and multiple raceways

Where conductors are installed in parallel in multiple raceways, bonding must preserve continuity in each path consistent with 250.102 and the parallel EGC rules in 250.122(F). Do not assume one bonding jumper on one conduit covers sister conduits.

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Equipment grounding connections that double as bonding

Wire-type EGCs terminate on equipment grounding terminals and bars; those connections bond the enclosure to the EGC network. Cord-and-plug connected equipment uses the equipment grounding conductor of the cord. Fixed equipment often uses a wire-type EGC pulled with the circuit conductors, or a qualifying metal raceway.

250.96 addresses bonding other enclosures: metal raceways, cable trays, cable armor, etc., must be metallically joined into a continuous EGC path. 250.97 covers bonding for over 250 volts to ground—additional bonding at certain fittings may be required so continuity does not rely on locknuts alone.

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Worked continuity scenarios

Scenario 1 — 60 A feeder in EMT. EMT with listed fittings wrench-tight can serve as the EGC under 250.118. If the inspector requires a wire-type EGC anyway, Table 250.122 copper minimum for 60 A is 10 AWG.

Scenario 2 — PVC conduit feeder. PVC is not an EGC. Pull a wire-type EGC sized from Table 250.122 and bond metal boxes/enclosures to that conductor.

Scenario 3 — Flexible connection at a motor. Short FMC/LFMC may qualify as EGC within 250.118 limits; longer or unqualified flex needs a wire-type EGC bonding the motor to the circuit EGC. Size the wire from the motor circuit protective device via Table 250.122.

Scenario 4 — Service vs feeder bonding jumper. A bonding jumper on the supply side of the service disconnect follows 250.102(C). A bonding jumper on a load-side feeder trough follows Table 250.122 sizing logic for equipment bonding jumpers.

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Timed open-book tips

Tab 250.90, 250.96, 250.97, 250.102, and 250.118. On every bonding question, ask first: supply side or load side? Then ask: is the raceway allowed as the EGC, or is a wire jumper required? That two-question filter prevents most Article 250 mix-ups on Prov’s six Grounding and Bonding items.