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 across the state. The CEC is built on the 2023 edition of the National Electrical Code (NEC) but layers in California-specific amendments that carry the force of law. The grounding and bonding rules sit in Article 250, and they govern everything from the electrodes in the earth to the conductors tying your panel, equipment, and metal piping back to ground.
What Code Applies and When
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 governs the design, installation, and maintenance of electrical systems for buildings and structures statewide, and compliance with its grounding and bonding provisions is mandatory for permit issuance and inspection approval by local enforcing agencies.
The 2025 edition is based on NFPA 70 (2023) with California amendments adopted during the 2024 Triennial Code Adoption Cycle.2NFPA. 2025 California Electrical Code Updates Most of Article 250 follows the NEC directly. Where California departs, it does so in targeted ways discussed further down.
The Grounding Electrode System
Every building’s electrical system needs a physical connection to earth. That connection limits voltage from lightning and line surges and gives the system a stable reference point. Under Section 250.52, if any of the following electrodes exist at a building, they must be bonded into the grounding electrode system:
- Metal underground water pipe in direct contact with the earth for at least 10 feet, electrically continuous with bonding jumpers around meters and dielectric fittings.
- A metal building frame with at least 10 feet of vertical contact with the earth, whether or not encased in concrete.
- A concrete-encased electrode (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 contact with the earth. Rebar sections can be tied together with steel tie wires or welded.
- A ground ring of bare copper no smaller than 2 AWG, encircling the building at a minimum depth of 30 inches and totaling at least 20 feet.
When none of those electrodes are available, a made electrode has to be installed. The common option is a driven ground rod: at least 5/8 inch in diameter with a minimum of 8 feet in contact with soil. If rock prevents driving it vertically, the rod can be driven at an angle or buried horizontally in a trench at least 30 inches deep.
The 25-Ohm Rule
A single ground rod has to achieve a resistance to earth of 25 ohms or less. If it doesn’t, a supplemental electrode is required, spaced at least 6 feet from the first. Many installers skip the resistance test entirely and drive two rods from the start, which satisfies the code without needing a ground resistance tester on site.
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, keyed to the size of the largest ungrounded 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. For parallel conductors, add up the total circular mil area and read the table against that combined figure.
The table size can be reduced depending on which electrode the GEC serves:
- Ground rod, pipe, or plate electrode: the GEC need not be larger than 6 AWG copper.
- Concrete-encased electrode: the GEC need not exceed 4 AWG copper.
- Metal underground water pipe as the sole electrode: no reduction; size the GEC to the full Table 250.66 value.
Where the GEC is exposed, it must be securely fastened. A 6 AWG or larger copper GEC can run along building surfaces without additional covering if it is not subject to physical damage. Anywhere physical damage is a risk, the conductor has to be protected inside rigid metal conduit, intermediate metal conduit, EMT, PVC conduit, or cable armor. Any GEC smaller than 6 AWG must always be enclosed in one of those 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 serve as a conductor 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 back 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 must be continuous end to end, with no switches, fuses, or other interrupting devices in the path.
Minimum EGC size is set by the rating of the overcurrent device on the circuit, per NEC Table 250.122.4UpCodes. NFPA 70 2023 – 250.122 Size of Equipment Grounding Conductors Common values:
- 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
Where 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. Rigid metal conduit, intermediate metal conduit, and EMT are all recognized as equipment grounding paths in themselves, provided every joint maintains electrical continuity through clean threads, tight fittings, and firmly seated locknuts.
Bonding at the Service, and Why Subpanels Are Different
At the service entrance, the grounded conductor (neutral) and the equipment grounding conductor are bonded together. That single connection, made by the main bonding jumper, establishes the electrical system’s reference to ground and gives fault current a path back to the source. The main bonding jumper is sized from NEC Table 250.102(C)(1) based on the largest ungrounded service-entrance conductor.5UpCodes. NFPA 70 – 250.102 Bonding Conductors and Jumpers
This bond happens at one point only. Every panel downstream from the service, commonly a subpanel, must keep the neutral and equipment grounding conductors separated. A subpanel needs a four-wire feed: two hots, a neutral, and a separate equipment grounding conductor. The neutral bus in the subpanel has to be isolated from the enclosure. Bond neutral to ground in a subpanel and you create a parallel return path for neutral current through the metal conduit and enclosures, which is both a shock hazard and an inspection failure.
Separately Derived Systems
A separately derived system is an electrical source with no direct connection to any other system’s circuit conductors, apart from grounding and bonding. Step-down transformers and standby generators that don’t feed neutral current through to the utility are the usual examples. Each one creates a new voltage source and needs its own grounding and bonding treatment.
For a transformer-type separately derived system, three pieces have to line up:
- A system bonding jumper connects the secondary neutral to the equipment grounding conductor, installed at either the transformer secondary or the first downstream disconnect, but not both. The grounding electrode conductor terminates at the same point.
- A supply-side bonding jumper connects the transformer enclosure to the secondary disconnect enclosure. Rigid or intermediate metal conduit can perform this function; nonmetallic or flexible raceways require a separate wire-type bonding jumper sized per Table 250.102(C)(1).
- The grounding electrode conductor connects to the building’s existing grounding electrode system and is sized per Table 250.66 against the secondary conductors.
An exception permits the system bonding jumper at both the transformer and the first disconnect when the transformer is outdoors and feeds a building through a feeder, so long as the arrangement doesn’t create a parallel neutral current path. That exception is what makes outdoor pad-mount transformers serving commercial buildings workable.
When a building contains more than one separately derived system, each can use a grounding electrode conductor tap connected to a common GEC. The common conductor must be at least 3/0 AWG copper or 250 kcmil aluminum, run without splices to the building’s grounding electrode system. Tap connections have to use listed connectors, busbars at least 1/4 inch by 2 inches, or exothermic welding.
Bonding Metal Piping
Metal piping that could become energized through contact with electrical wiring or equipment must be bonded to the grounding system. Metal water piping is already handled through 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 is sized from Table 250.122 based on the circuit that could energize the pipe. If a gas furnace is fed by a branch circuit whose EGC reaches the appliance, that EGC satisfies the gas pipe bonding requirement. A separate bonding conductor is only needed where the piping could be energized by a circuit that doesn’t already carry an EGC to it.
Pools, Spas, and Solar
Two scenarios come up often enough in California to be worth calling out on their own, and both go beyond the standard building grounding rules.
Pool and Spa Equipotential Bonding
Pools, spas, and hot tubs are covered by NEC Article 680. The goal is equipotential bonding: bringing every conductive surface in and around the pool to the same electrical potential so 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 no smaller than 8 AWG. These bonding conductors are not required to extend back to the panelboard or grounding electrode system; their job is equalization, not fault clearing. Perimeter surface bonding extends 3 feet horizontally beyond the inside walls of the pool. Where the pool shell contains structural reinforcing steel, that steel serves as the bonding grid; where rebar is not available or is coated, 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.
Following the 2023 NEC, the 2025 CEC allows 40-percent copper-clad steel conductors as an alternative to solid copper for equipotential bonding around permanently installed pools.
Solar PV Grounding
Under NEC Article 690, every exposed metal part of a photovoltaic system, including module frames, racking, junction boxes, and inverter enclosures, must be grounded regardless of system voltage. An equipment grounding conductor has to run between the array and associated equipment, and it must be routed with the circuit conductors when those conductors leave the array area.
Listed grounding devices can bond module frames directly to the metal mounting structure, and that structure can then serve as the equipment grounding path when it is identified for that purpose and includes bonding jumpers between separate sections. Adjacent modules can be bonded frame-to-frame with listed devices, which simplifies larger roof arrays. EGC sizing follows the same Table 250.122 used for other branch circuits, keyed to the overcurrent device protecting the circuit.
California-Specific Amendments Worth Knowing
Two amendments are the ones most likely to surface on a real job. Healthcare facilities must use insulated copper equipment grounding conductors with green insulation for branch circuits in patient care areas, 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 New single-family homes must also be built energy-storage-ready, with dedicated raceways and minimum panelboard busbar ratings.
Permits, Inspections, and the OSHA Overlay
Electrical work in California requires a permit whenever a system is installed, altered, repaired, replaced, or remodeled, unless the CEC specifically exempts the work. Panel upgrades, new circuits, and grounding system modifications are all included. The process varies by jurisdiction but generally involves submitting an application, paying a fee, doing 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 get verified.
Employers also fall under federal OSHA electrical safety standards on top of the CEC. Under 29 CFR 1910.304, all 15- and 20-ampere receptacles in the workplace must be grounding-type, with grounding contacts effectively connected to the circuit’s equipment grounding conductor, and grounding terminals cannot be repurposed for anything other than grounding. Where an older building has ungrounded receptacle boxes with no grounding path available, OSHA allows three replacement options: another non-grounding receptacle, a GFCI receptacle marked “No Equipment Ground,” or a grounding-type receptacle downstream of a GFCI device, also marked to indicate no equipment ground is present.7Occupational Safety and Health Administration. 1910.304 – Wiring Design and Protection Construction sites with temporary wiring that lack GFCI protection must run a written assured equipment grounding conductor program, with daily visual inspections of cords and receptacles and a designated competent person overseeing it.
OSHA violations for electrical grounding deficiencies carry penalties of up to $16,550 per serious violation, and willful or repeated violations can reach $165,514 per instance.8Occupational Safety and Health Administration. 2025 Annual Adjustments to OSHA Civil Penalties Improper grounding is one of the recurring citations in that category.