NEC-Standard Typical Residential Wiring Diagram and Electrical Installation Requirements from NEC

NEC-Standard
Typical Residential Wiring Diagram and Electrical Installation Requirements from NEC

SUPPLY
Domestic supply is usually 2 phases (120 V/240 V - 60 Hz). 2 phases + neutral are supplied. Neutral is re-earthed at entry. Earth is local.

METER
Usually a weatherproof unit outside the house.

SERVICE PANEL
Ratings of 60 A, 100 A, 150 A and 200 A exist. The Service Panel (or Service Entrance Panel) usually contains a Main Disconnect device and the necessary protective devices for the sub-circuits.

POWER CIRCUITS
Appliances having heavy power consumption (ranges, water-heaters, etc.) are supplied on a specific circuit, often 120/240 V. Various socket outlets of appropriate ratings are available, these are noninterchangeable, thus 2 Phase + Neutral + Earth plug cannot be fitted to a 2 Phase + Earth socket, etc.

GENERAL PURPOSE CIRCUITS
These are 120 V-15 A and supply socket outlets (IP+N+G).These circuits supply bedrooms, etc. where the use of a large number of appliances is unlikely. Note that all general purpose socket outlets must be of the grounding type.

APPLIANCE CIRCUITS
The 120 V-20 A circuits supply areas such as kitchens,dining-rooms. etc., when there is a likelihood of more intensive use of appliances. The NEC [National Electrical Code) requires at least two appliance circuits for a domestic installation.Only socket outlets may be supplied on an appliance circuit. All domestic use NEMA 5-15R and 5-20R receptacles must be tamper resistant.

PLUGS
Various types of plugs exist to match the various configurations of socket outlets.

OUTDOORS
Outdoor socket outlets must have 6 mA GFCI protection and be housed in a weatherproof enclosure.

GROUND-FAULT CIRCUITINTERRUPTERS
(GFCI)
All domestic use 125 V - 15 A and 20 A socket outlets in the following locations must be protected by GFCI having a trip level sensitivity of 6 mA:
- Bathrooms
- Garages
- Kitchens
- Basements
- Outdoors
- Laundry and utility sinks (when socket outlets are within 6 feet).

ARC-FAULT CIRCUITINTERRUPTERS
(AFCI)
All domestic use 120 V - 15 A and 20 A branch circuits supplying outlets in living rooms, dining rooms, family rooms, bedrooms and similar areas must be AFCI protected.

TAMPER RESISTANT
(SHUTTERED) SOCKET OUTLETS
All domestic use 125 V - 15 A and 20 A socket outlets must be Tamper Resistant (shuttered).

EARTHING (GROUNDING)
The use of ungrounded (2P) sockets in domestic installations is no longer allowed by the NEC. Earth can be distributed in the installation in one or two ways:
- By a specific earth conductor distributed along with live + neutral
- By using metallic boxes, conduit and sheathed cables and using this metallic system as earth.
All conductive non-current carrying parts of the electrical system should be effectively bonded to earth.

Polarity:
Polarity is conserved throughout the installation.

Live (hot):
Terminal screws brass colour; conductors insulated in black

Neutral:
Terminal screws silver or marked white or W; conductor insulated in white.

Ground:
Terminals green colour or marked G; conductors insulated in green or wire is left bare.

Cabling:
Various types of cables are used in domestic installations, the most frequent are:

NM. Non-metallic sheathed; AC, Metal-clad cable.

Similarly various types of conduits are also encountered:
- Rigid steel conduit
- Intermediate metal conduit
- Thinwall metal conduit
- Flexible metal conduit
- Rigid non-metallic conduit
- Surface raceway.

ELECTRICAL ACCESSORY
INSTALLATION
Accessories are fitted in standard boxes, either metal or plastic, the most common sizes being 2 inches by 4 inches and 4 inches by 4 inches.