California electrical code grounding requirements come from the 2025 California Electrical Code (CEC), which took effect January 1, 2026 and applies to all new electrical installations and major modifications statewide. The CEC is codified as Title 24, Part 3 of the California Code of Regulations and is maintained by the California Building Standards Commission.1California Department of General Services. California Building Standards Commission Codes It is built on the 2023 edition of the National Electrical Code (NFPA 70), with California amendments adopted during the 2024 Triennial Code Adoption Cycle.2NFPA. 2025 California Electrical Code Updates Grounding and bonding rules live in Article 250, covering everything from the electrodes buried in the earth to the conductors that tie your panel, equipment, and metal piping back to ground.
The Grounding Electrode System
The grounding electrode system (GES) is the physical link between your building’s electrical system and the earth. It limits voltage from lightning and line surges and gives the whole system a stable reference point. Article 250 (following NEC Section 250.52) tells you which electrodes qualify, and if certain electrodes already exist at the building, you have to use them.
Electrodes That Must Be Bonded When Present
- Metal underground water pipe with at least 10 feet (3 meters) of direct earth contact. The pipe must be electrically continuous, which means bonding jumpers around water meters and dielectric fittings.
- The structural metal frame of a building, when it has at least 10 feet of vertical contact with the earth, with or without concrete encasement.
- A concrete-encased electrode, also called a Ufer ground: at least 20 feet of bare copper conductor (4 AWG minimum) or half-inch-or-larger steel rebar, encased in a minimum of 2 inches of concrete in direct earth contact. Multiple rebar pieces can be tied together with steel tie wires or welded.
- A ground ring of bare copper conductor at least 2 AWG, encircling the building in direct earth contact at a minimum depth of 30 inches, at least 20 feet long.
When none of those are available, a made electrode has to be installed. The most common is a driven ground rod at least 5/8 inch in diameter with at least 8 feet in contact with the soil. If rock prevents vertical driving to full depth, the rod can go in at an angle or be buried horizontally in a trench at least 30 inches deep.
The 25-Ohm Rule
A single ground rod must achieve a resistance to earth of 25 ohms or less. If it does not, a second supplemental electrode is required, spaced at least 6 feet from the first. Many electricians simply install two rods from the start, which avoids ever needing a ground resistance tester to prove the single rod meets the threshold.
Sizing the Grounding Electrode Conductor
The grounding electrode conductor (GEC) runs from the service equipment enclosure to the grounding electrode system. Its minimum size comes from NEC Table 250.66, based on the size of the largest ungrounded (hot) service-entrance conductor.3UpCodes. NFPA 70 2023 – 250.66 Size of Alternating-Current Grounding Electrode Conductor A service with 4/0 AWG copper ungrounded conductors, for example, requires at least a 2 AWG copper GEC. When parallel conductors are used, add their total circular mil area and run that combined figure against the table.
You can reduce the table size depending on which electrode the GEC terminates at:
- For a ground rod, pipe, or plate electrode, the GEC need not be larger than 6 AWG copper.
- For a concrete-encased electrode, the GEC need not exceed 4 AWG copper.
- For a metal underground water pipe serving as the sole electrode, no reduction is allowed. The GEC must meet the full Table 250.66 requirement.
The GEC must be securely fastened where exposed. It can run along building surfaces without additional covering if it is 6 AWG or larger copper and not exposed to physical damage. Where damage is a risk, it must be protected inside rigid metal conduit, intermediate metal conduit, electrical metallic tubing, PVC conduit, or cable armor. Any GEC smaller than 6 AWG always has to be enclosed in one of those protective methods. Where the GEC connects to interior metal water piping, that connection must be within 5 feet of the pipe’s point of entry into the building. Piping beyond that 5-foot point cannot be used to interconnect grounding electrodes.
Equipment Grounding Conductors on Branch Circuits
The equipment grounding conductor (EGC) is the safety path installed with each branch circuit. It ties metal enclosures, conduit, outlet boxes, and equipment frames back to the service ground. When a fault energizes a metal part that shouldn’t be hot, the EGC carries enough current to trip the breaker or blow the fuse quickly. That low-impedance path is what keeps a short circuit from becoming an electrocution. The EGC has to be continuous end to end, with no switches, fuses, or other interrupting devices in its path.
Minimum EGC size comes from NEC Table 250.122 and is driven by the rating of the overcurrent protective device on the circuit.4UpCodes. NFPA 70 2023 – 250.122 Size of Equipment Grounding Conductors Common sizes:
- 15-ampere breaker: 14 AWG copper minimum
- 20-ampere breaker: 12 AWG copper minimum
- 60-ampere breaker: 10 AWG copper minimum
- 100-ampere breaker: 8 AWG copper minimum
- 200-ampere breaker: 6 AWG copper minimum
When multiple circuits share a raceway or cable, a single EGC sized for the largest overcurrent device in that raceway is permitted. The EGC is never required to be larger than the circuit’s phase conductors.
Metal Conduit as the Equipment Grounding Path
Rigid metal conduit (RMC), intermediate metal conduit (IMC), and electrical metallic tubing (EMT) are all recognized as equipment grounding conductors. The tradeoff is that every joint in the raceway has to maintain electrical continuity. Threads need to be clean and undamaged, fittings must be tight, and locknuts must seat firmly. Connections to enclosures on circuits under 250 volts to ground can use two locknuts (one inside, one outside) for RMC or IMC. Service raceways are stricter and cannot rely on locknuts alone; they require threaded hubs or bonding-type fittings.
Any paint or nonconductive coating at a connection point has to be removed unless the locknut cuts through it during installation. Expansion fittings and telescoping conduit sections break the grounding path by design, so they need a bonding jumper across the joint or must be listed for grounding use.
Service Bonding and Why Subpanels Are Different
At the service entrance, the grounded conductor (neutral) and the equipment grounding conductor must be bonded together. This single connection, made by the main bonding jumper, establishes the system’s reference to ground and gives fault current a path back to the source so the breaker trips. The main bonding jumper is sized using NEC Table 250.102(C)(1), based on the size of the largest ungrounded service-entrance conductor.5UpCodes. NFPA 70 – 250.102 Bonding Conductors and Jumpers
That bonding happens at one location only. Every panel downstream from the service, commonly called a subpanel, must keep neutral and equipment grounding conductors separated. A subpanel needs a four-wire feed: two hots, one neutral, and one separate equipment grounding conductor. The neutral bus in the subpanel has to be isolated from the panel enclosure. Bonding neutral to ground in a subpanel creates a parallel return path for neutral current through the metal conduit and enclosures. That current on metal parts is both a shock hazard and an interference problem, and it will fail inspection.
Separately Derived Systems
A separately derived system is an electrical source with no direct connection to any other system’s circuit conductors except through grounding and bonding. The most common examples are step-down transformers and standby generators that are not configured to feed neutral current through to the utility system. These need their own grounding and bonding because they create a new voltage source that is electrically isolated from the service.
Key requirements for a transformer-type separately derived system:
- A system bonding jumper connects the secondary neutral to the equipment grounding conductor. It must be installed at either the transformer secondary or the first disconnecting means downstream, but not both. The grounding electrode conductor must terminate at the same point where this bonding jumper is connected.
- A supply-side bonding jumper connects the transformer enclosure to the secondary disconnect enclosure. Rigid or intermediate metal conduit can serve this function if it provides the raceway path. Nonmetallic or flexible raceways require a separate wire-type bonding jumper sized per Table 250.102(C)(1).
- The grounding electrode conductor must connect to the building’s existing grounding electrode system and is sized per Table 250.66 based on the secondary conductors.
An exception allows the system bonding jumper at both the transformer and the first disconnect when the transformer is outdoors and feeds a building through a feeder, as long as the arrangement does not create a parallel neutral current path. That exception matters for outdoor pad-mount transformers serving commercial buildings.
Where multiple separately derived systems exist in a building, each can use a grounding electrode conductor tap connected to a common grounding electrode conductor. That common conductor has to be at least 3/0 AWG copper or 250 kcmil aluminum and must run without splices to the building’s grounding electrode system. Tap connections must use listed connectors, busbars at least 1/4 inch thick by 2 inches wide, or exothermic welding.
Metal Piping and Gas Lines
Any metal piping system that could become energized through contact with electrical wiring or equipment has to be bonded to the grounding system. Metal water piping is already bonded as part of the grounding electrode system when it qualifies as an electrode. Other metal piping, including gas piping, must be bonded to the equipment grounding conductor of the circuit likely to energize it, or to the service equipment enclosure, grounded service conductor, or a grounding electrode.
The bonding conductor for gas piping and similar systems is sized from Table 250.122 based on the rating of the circuit that could energize it. In practice, if a gas furnace is supplied by a branch circuit with an EGC, that EGC satisfies the gas pipe bonding requirement. A separate bonding conductor is only needed when the piping could be energized by a circuit that doesn’t already include an EGC routed to it.
Pools, Spas, and Equipotential Bonding
Pools, spas, and hot tubs have dedicated bonding requirements under NEC Article 680 that go beyond standard building grounding. The goal is equipotential bonding: bringing every conductive surface in and around the pool to the same electrical potential so that a person in the water cannot become the path between two different voltages.
All metallic parts of the pool structure, reinforcing steel, metal fittings, ladders, handrails, diving boards, water heaters, pump motors, and light fixtures must be bonded together with solid copper or copper-clad steel conductors no smaller than 8 AWG. These bonding conductors connect everything to a common point. They are not required to extend back to the panelboard or grounding electrode system because their job is equalization, not fault clearing.
The perimeter surface bonding extends 3 feet horizontally beyond the inside walls of the pool. Where the pool shell contains structural reinforcing steel, that steel itself serves as the bonding grid. Where rebar is not available or is encapsulated in a nonconductive coating, a copper conductor grid or perimeter ring has to be installed 4 to 6 inches below the deck surface and connected to the pool bonding system at a minimum of four uniformly spaced points around the pool.
Following the 2023 NEC, the 2025 CEC also allows 40-percent copper-clad steel conductors as an alternative to solid copper for equipotential bonding around permanently installed pools.
Solar Photovoltaic System Grounding
Rooftop solar is governed by NEC Article 690. Every exposed metal part of a PV system, including module frames, racking, junction boxes, and inverter enclosures, must be grounded regardless of system voltage. An equipment grounding conductor must run between the array and associated equipment and be routed with the circuit conductors when those conductors leave the array area.
Listed grounding devices can bond PV module frames directly to the metal mounting structure, and the mounting structures can then serve as the equipment grounding path if they are identified for that purpose and have bonding jumpers between separate sections. Adjacent modules can be bonded frame-to-frame using listed devices designed for that purpose, which simplifies installation on large roof arrays. The EGC for PV circuits is sized based on the overcurrent device protecting the circuit, following the same Table 250.122 used for other branch circuits.
California-Specific Amendments to Watch
Most of Article 250 follows the NEC directly, but California adds requirements in specific areas. In healthcare facilities, branch circuits in patient care areas must use insulated copper equipment grounding conductors with green insulation, and panelboards serving the same patient care vicinity must have their grounding terminal buses bonded together with a continuous copper conductor no smaller than 10 AWG.6California Department of General Services. 2025 Title 24 Part 3 California Electrical Code California also requires energy storage system readiness in new single-family homes, including dedicated raceways and minimum panelboard busbar ratings. Check the state amendments against the base NEC text before signing off on any design.
Permits and Inspection
Electrical work in California requires a permit whenever a system is installed, altered, repaired, replaced, or remodeled, unless the CEC specifically exempts the work. That includes panel upgrades, new circuits, and grounding system modifications. The process varies by jurisdiction but generally involves submitting an application describing the scope of work, paying a fee, performing the work, and scheduling an inspection before anything is concealed behind walls or concrete. The inspection is where the grounding electrode system, conductor sizing, bonding connections, and subpanel separation all get verified. Failing an inspection means corrective work and a re-inspection fee, so the details matter the first time through.