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Electrical Installation of Residential Services
Information provided on this page references the 2007 California Electric Code (CEC).
- Service Entrance
- Service Grounding / Bonding
- Grounding Electrodes [250.52]
- Grounding Electrode Conductor
- Other Bonding Requirements
Minimum Size of Residential Service & Feeder Conductors [CEC 310.15(B)(6)]
Conductor Types must be rated for "wet" locations. Conductors exposed to sunlight must be listed/marked "sunlight resistant." [310.8] e.g.: Type THWN conductors.
See Table 310.15(B)(6) for complete list of amperes and conductor types.
Clearances for Service Drops [CEC 230.9 & 230.24]
- 3 feet from openable:
- Fire escapes
- Windows and similar locations
- 8 feet above any roof surface with a pitch of less than 4 in 12.
- 3 feet above any roof surface with a pitch greater than 4 in 12.
- 18 inches when passing over the overhang (eave) portion of the roof, regardless of the pitch, provided the overhang does not exceed 4 feet and the length of the drop above the overhang does not exceed 6 feet
- 10 feet above grade at the service entrance, also at lowest point of the drip loop, and above areas that are accessible only to pedestrians.
- 12 feet above residential property and driveways.
- 1 foot from communications wires/cables at any point in the span including the point of attachment to the building. [800.10(A)(4)]
Service Mast [230.28]
Only service conductors shall be attached to the mast.
Service Grounding / Bonding
- An unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service disconnect enclosure to the grounded conductor (neutral) of the system within the enclosure [250.28]
- Service equipment, enclosures and raceways must be bonded. [250.92(A)] Bonding shall apply at each end, and to all intervening raceways, boxes, and enclosures, between the service equipment and the grounding electrode
Acceptable Bonding Techniques
The following are acceptable bonding techniques according to [250.92(B)]:
- Threadless conduit fittings, both setscrew and compression types
- Note: standard locknuts must be upgraded to the bonding type
- Bonding bushings with jumpers that must be used when concentric knockouts are encountered
Grounding Electrodes [250.52]
In the City of Daly City, grounding electrodes for residential service must be A, and either B or C as follows:
- A metal underground water pipe in direct contact with the earth for 10 feet or more and electrically continuous by bonding around insulating joints to the points of connection of the grounding electrode conductor. Interior metal water piping located more than 5 feet from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system
- A concrete encased electrode: an electrode encased by at least 2 inches of concrete, located within and near the bottom of a concrete foundation or a footing that is in direct contact with the earth, consisting of at least 20 feet of one or more bare or zinc galvanized steel reinforcing bars or rods (rebar) of not less than ½ inch in diameter, or of at least 20 feet of bare copper conductor not smaller than 4 AWG. Rebars shall be permitted to be bonded together by the usual steel tie wires or other effective means
- A ground rod, copper or copper clad plated steel, ½ to 5/8 inches in diameter and 8 to 10 feet long, driven at least 8 feet into the ground
- For other types of grounding electrodes and installation procedures refer to NEC 250.52 and.53
- Two different types of grounding electrodes are required; for service upgrades this usually means the water pipe and a ground rod
The Grounding Electrode Conductor (GEC)
Materials (DCMC 15.24.070)
- Copper: solid, stranded, bare or insulated
- Number 8 AWG (minimum size); requires physical protection [250.64(B)]
- Number 6 AWG; requires protection if subject to physical damage
- Number 4; requires protection if subject to severe physical damage (e.g. along driveway).
Protection is usually in the form of EMT, armor cable or rigid conduit. All of these methods must be properly bonded at both ends. [250.64(E)]
The GEC shall be installed in one continuous length without a splice or joint, unless spliced only by listed irreversible compression-type connectors.
GEC Connection to Electrode
- The connection is to be accessible unless buried or encased in concrete [250.68 (A)]
- The connection is to be made with listed lugs, clamps or other listed materials
Note: if buried, the lug or clamp must be listed for ground contact. [250.70]
GEC Connection at the Service
The GEC shall be connected to the grounded service conductor (neutral). [250.24(C)]
This connection typically occurs at the neutral terminal of the main disconnect enclosure.
Capacity of GEC (Table 250.66)
- Number 8 AWG is rated for a number 2 AWG size service entrance conductor; number 6 AWG up to size number 1/0, and number 4 AWG up to number 3/0
- The GEC to a ground rod need not exceed number 6 AWG in size [250.66(A)]
- The GEC to a concrete encased electrode need not exceed number 4 AWG in size [250.66(B)]
Other Bonding Requirements [250.104]
Bonding of Piping Systems
- Metal Water Piping systems installed in, or attached to a building, shall be bonded to the service equipment enclosure, the grounded conductor (neutral) at the service, the GEC where of sufficient size, or to the one or more grounding electrodes used. The bonding jumpers shall be sized in accordance with Table 250.66.
- Other Metal Piping, where installed in or attached to a building, including gas piping, that may become energized shall be bonded to the service equipment enclosure, the grounded conductor (neutral) at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used.
The points of attachment of the bonding jumper(s) shall be accessible.
Working Space Required at the Service [110.26 (A) - (E)]
- 6 feet and 6 inches of headroom
- 30 inches minimum width
- 36 inches minimum depth measured from the face of enclosure
- Meter height:
- 48 inches
- 66 inches (PG&E)
- Illumination shall be provided for working space at service equipment installed indoors.
Daly City Municipal Code (DCMC) Requirements
- (DCMC 15.24.030): service entrance conductors shall be enclosed in rigid metal conduit (RMC). Note: PG&E requires a minimum of 1 and 1/4 inch diameter service mast
- (DCMC 15.24.070): conductor material shall be copper only
- (DCMC 15.24.040): the meter and main disconnect must be accessible from the exterior. Note: a lockable, gated entry compromises this access requirement
- (DCMC 15.24.040): the service equipment must be screened from public view by an enclosure
Panel Directory / Circuit Directory [408.4]
All circuits shall be legibly identified as to the purpose or the use on a circuit directory located on the face or inside of the panel door.
Grounded Conductor [200.6(A)(1-3)]
Color: an insulated grounded (neutral) conductor of 6 AWG and smaller shall be identified by a continuous white outer finish along its entire length [200.6(A)]. This means you cannot re-color a conductor to make it white for these sizes.
An insulated grounded (neutral) conductor larger than 6 AWG can be re-colored in the field; this re-coloring must occur at time of installation, by a distinctive white or gray marking at its termination [200.6(b)(3)]
Terminations: each grounded (neutral) conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor [408.41]. I.e. One conductor, one screw.
Circuit Breakers & Size of Conductors [240.4(D)]
- 14 AWG size conductors are limited to 15 ampere rated breakers
- 12 AWG size conductors are limited to 20 ampere rated breakers
Service Drop [230.54]
Service heads shall be located above the point of attachment of the service conductors to the building.
Rating of Cabinet / Service Equipment
All cabinets installed outdoors must be rated NEMA 3 (this includes cabinets within enclosures designed to 'screen equipment from public view').