Systems Of Wiring Buildings There are three general systems of arranging the conductors within a building for electric lightingpurposes. Tree or Single Main System, Subdivided Main System, Three-Wire System.

The Tree Or Single Main System

Subdivided Main System

The three-wire system

DISTRIBUTION BOARDS

Electrical System Must meet several conditions to be satisfactory: Be safe Be convenient Be expandable Look neat Provide sufficient current

Service Entrance Electrical power comes by overhead or underground wires Power company provides: Transformer Service drop Appropriate wiring to entrance head

Service Entrance Transformer: converts high voltage from power lines to 240 volts for home and farm installations Service drop: assembly of electrical wires, connectors, and fasteners used to transmit electricity from transformer to entrance head to service entrance panel

Service Entrance Entrance head: waterproof device used to attach exterior wires to interior wires of a building Modern systems – most have entrance cables buried underground No need for entrance head Service entrance panel: box with fuses or circuit breakers where electricity enters a building

Branch Circuits Most circuits begin from service entrance panel Called branch circuits because they branch out into a variety of places and for a variety of purposes Generally includes only one motor or a series of outlets or a series of lighting fixtures Important to provide correct size of wire and fuse or circuit breaker for load on each circuit

Branch Circuits Fuse: plug or cartridge containing a strip of metal that melts when more than a specified amount of current passes through it Must be replaced if it blows Circuit breaker: a switch that trips and breaks the circuit when more than a specified amount of current passes through it Can be reset after being tripped

Branch Circuits Fuses and circuit breakers designed to protect circuits from damage and fire Installing fuses or breakers with a larger ampere rating than recommended for size of wire being protected destroys protection

ISI CODES IS No. DESCRIPTION IS 2705 CT for measuring and protection IS 373 Bus bar arrangement and marking IS 1248 - 1958 Meter (measuring) IS 3072 - 1975 Installation of Switch gear IS 3043 Code of practice for earthing. IS 8106 - 1966 Selection, Installation and maintenance of fuses upto 650V IS 8828 - 1978 Marking and arrangement of switch gear Bus bar main Connectors and auxiliary wiring. IS 9926 - 1981 Cubical Board. IS 1554 Insulated conductor rating.   IS 1753 Enclosed distribution switchboard and cutout for Voltage not exceeding 100 V.

IS 961 Miniature circuit breaker. IS 732 Fuse wire use in rewirable type electric fuses upto 650V. IS 1646 PVC insulated electric cable heavy-duty. IS 1653 Aluminium conductor for insulated cable. IS 961 Recommended current rating for cable. IS 732 Code of practice for electrical wiring installation system Voltage not exceeding 650 V. IS 1646 Code of practice for wire safety of building (general) Electrical installation.   IS 694 PVC insulated cables (wire).  IS 2509 Rigid non metallic conduits for electrical wiring. IS 6946 Flexible (playable) non metallic conduit for electrical Installation.  

IS 1293 Three pin plugs and sockets. IS 818 Conductor for insulated electrical cables and flexible codes. IS 9537-1980 Specification for conduit for electrical installation. IS 3419 Accessories for non metallic conduit for electrical wiring. IS 3854 Switches. IS 6538 Plugs. IS 2834 - 1954 Capacitor. IS 1913 - 1969 General safety requirement for lighting fitting. IS 2944 - 1969 Code of practice for lighting public thorough fares.

IS 3528 Water proof electrical lighting fitting. IS 3553 - 1958 Water tight electrical lighting fitting. IS 1229 - 1958 Mild steel tubular and other wrought steel pipe fitting. IS 2149 - 1970 Luminaries and street light. IS 9224 HRC fuses having rupturing capacity of 90 KA. IS 2312 - 1967 Exhaust Fan. IS 374 - 1976 Class – I Ceiling Fan.

ELCB AND MCB “MCB” is an acronym of Miniature circuit breaker “ELCB” is an acronym for Earth Leakage Circuit Breaker. This component is designed to detect electric current leakage in a house wiring and appliances connected to the wiring. The leakage current (or leakage voltage) occurs because of defect in a part of the installation, which can be caused by faulty components or by injuries to the insulation of the wiring, cables, electrical appliances or other accessories such as the switches and socket outlets. When there is leaked current that exceeds the preset value of the ELCB setting, the ELCB then breaks the connection of the incoming electricity supply from the internal house wiring.

A CLOSE VIEW OF MCB

MCB Characteristics

Advantages of MCB’s over Fuses Tripped MCB readily identified even in darkness Cannot be switched back on while fault exists – trip free mechanism Enables supply to be restored immediately and easily even by untrained personnel Accepted as a circuit isolator Locking devices can be attached for maintenance purposes Do not normally require replacement ‘Single phasing’ of motors is not an issue Do not age in service Tamperproof

An ELCB unit inside a house electric panel A close-up view of the ELCB unit

Typical ELCB circuit generation of ELCB design.

the ELCB was actually a voltage-operated device that was designed to detect a current leaking through the earth path of electrical equipment and appliances. The circuit that you see here is actually a residual current devise (RCD), or residual current circuit breaker (RCCB).

Observe that the supply coil, the neutral coil and the search coil all wound on a common transformer core. On a healthy circuit the same current passes through the phase coil, the load and return back through the neutral coil. they will produce an opposing magnetic flux. when there is fault or a leakage to earth in the load circuit, or anywhere between the load circuit and the output connection of the ELCB circuit, the current returning through the neutral coil has been reduced. Then the magnetic flux inside the transformer core is not balanced anymore. The total sum of the opposing magnetic flux is no longer zero. This net remaining flux is what we call a residual flux. The periodically changing residual flux inside the transformer core crosses path with the winding of the search coil. This action produces an electromotive force (e.m.f.) across the search coil. The induced voltage across the search coil produces a current inside the wiring of the trip circuit. It is this current that operates the trip coil of the circuit breaker. During tripping when a fault is detected, both the phase and neutral connection is isolated.

The test pushbutton and the test resistor are arranged and wired to provide a testing function for the ELCB circuit. This part of the circuit bleeds away a fraction of the running current from the phase coil, and sends it through the return coil.

HOUSE SINGLE LINE DIAGRAM

PLATE ELECTRODE EARTHING: Earthing electrode shall consist of plate, not lessthan 600 mm x 600 mm x 12 mm thick. The plate electrode shall be buried as far as practicable below permanent moisture level but, in any case, not less than 3 meters below ground level. Wherever possible, earth electrodes shall be located as near the water tap, water drain or near down take pipe. Earth electrodes shall not be installed in proximity to a metal fence. It shall be kept clear of the buildings foundations and in no case it shall be nearer than 2 meters from the outer face of the wall.

The earth plate shall be set vertically and surrounded with 150 mm thick layer of charcoal dust and salt mixture. 20 mm GI pipe shallrun from the top edge of the plate to the ground level. The top of the pipe shall be provided with a G.I. threaded cap for watering the earth through a pipe. The G.I. cap over the GI pipe shall be housed in a masonry chamber, approximately 300 mm x 300 mm x 300 mm deep. The masonry chamber shall be provided with a cast iron inspection cover resting over a GI frame, embedded in masonry.

PIPE ELECTRODE EARTHING: Earthing electrode shall consist of a CI pipe (class B of approved make), not less than 40 mm dia. and 3 meters long. CL pipe electrode shall be cut tapered at the bottom and provided with holes of 12 mm dia. drilled at 75 mm interval upto 2.5 meters length from bottom. The electrode shall be buried vertically in the ground as far as practicable below permanent moisture level, but in any case notless than 3 mtr. below ground level. The electrode shall be in one piece and no joints shall be allowed in the electrode. Wherever possible, earth electrodes shall be located close to water tap, water drain ora down take pipe.

Earth electrode shall not be located in proximity to a metal fence Earth electrode shall not be located in proximity to a metal fence. It shall be kept clear of the building foundations and in no case; it shall be nearer than 2 meters from the outer face of the wall. The pipe earth electrode shall be kept vertically and surrounded with 150mm thick layer of charcoal dust and salt mixture upto a height of 2.5 meters from the bottom. At the top of the electrode a G.I. threaded cap shall be provided for watering the earth. The main earth conductors shall be connected to the electrode just below the G.I. cap, with proper terminal lugs and check nuts. The G.I. cap over the CL pipe and earth connection shall be housed in a masonry chamber, approximately 300 mm length x 300 mm wide and 300 mm deep. The masonry chamber shall be provided with a cast iron inspection cover resting over a C.I. frame, embedded in masonry.