Building electric circuit

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Transcript of Building electric circuit

OUTLINE Electric Service

Single and Three-phase Electricity

Grounding and Ground Fault

Circuit Safe LoadSizing the Branch Circuit,

Conduit Pipes and the Overcurrent Protection

Device

BUILDING ELECTRIC CIRCUIT

ELECTRIC SERVICE

Service Entrance is defined as that portion of the supply

conductors which extends from the street main, duct or transformers to the services switch or switchboard of the building supply.

The NEC defines service entrance as “ the conductor and equipment for delivering energy from the electricity supply system to the writing system to the wiring system of the premises served.”

Service Entrance is either :

Overhead Service Entrance is the most common type employed by the

power companies supplying electricity

Underground Service Entrance consist of a raceway extending from the

building to the property line where it is tapped to the main.

Electric Service Metering

• Electric meter is normally installed outside the building or at the

property line wall or post for ready access to the meter reader and to make it difficult for tampering or

installing jumpers.

Electric Service Metering

• For multi-door service such as apartment and commercial buildings,

the use of a master metering is adopted where the battery of meters are installed in a central meter room or space to facilitate meter reading

making it a one step affair.

THE FEEDER

• is defined as “all circuit conductors between the service equipment, or the generator switchboard of an isolated plant, and the final branch circuit overcurrent device.

FEEDER is installed under the following considerations :

On large installations, each floor is provided with one feeder.

In small installations, 1 or 2 feeder is satisfactory.

Feeder for electric motor must be independent and totally separated from the light circuits.

Feeder requiring more than 50 mm (2’’) dia conduit pipe should not be used.

Feeder should be sub-divided if there are several bends or offsets on the line. A 50 mm conduit pipe is the largest diameter that could be economically used.

Feeders radiating from the distribution panel should be provided each with a properly rated switch and circuit breaker.

Good practice dictates that feeders aand main shall be installed insidea conduit pipe as it carries high voltage which special protection.

MAIN is a feeder interior wiring extending from

service switch, generator bus, or converter bus to the main distribution center or electric service equipments.

The service equipment location should be : Centrally located to shorten all home runs.

Branch Circuit run in excess of 30 meters will result to an excessive voltage drop.

Convenience to approach In residential houses, it should be located near

the load center. The heaviest load is the kitchen and the laundry are.

SINGLE and THREE PHASE ELECTRICITY

A single phase alternating current can either be 2 or 3 wires.

A 3 phase AC has 3 or 4 wires, it consists of 3 hot legs hot legs designated as A, B and C plus a neutral N.

The advantages of this system are :

The 120 v is for lighting and rreceptacles only.

The 240 v is for bigger loads.

Voltage drop is lower.

The service conductors are sized based on the 240 volts line rather than on the 120 volts, hence smaller wire is being used.

Conductors in a 3 phase connection is identified as:

neutral ............................ White or gray wires

First Hot Line A ................ Black Wires

Second Hot line B .......... Red wires

The neutral conductor carries no current when the loads on both sides of it are balanced or equal. Since it is Grounded it is at a neutral zero potential being ½ way in voltage between the hot line A and B.

SYSTEM AND UTILIZATION VOLTAGE

System voltage is what the power company like the Meralco and Electric Cooperative supplies current or what the transformer produces.

Utilization Voltage is the one being utilized after some normal voltage drop.

To Clarify a System and Utilization Voltages we have the following example :

when specifying transformers, use system voltages.

for motors, use utilization voltage.

Utilization voltage correspond to a 4% voltage drop considered as within the normal motor tolerance.

The purpose of grounding the system is to fix permanently to a zero voltage.

The NEC defines GROUND as zero voltage.

In the absence of ground, the system voltage may drift causing all kinds of control and protection problems.

The CODE so requires that all new installations shall use grounded outlets such as GFI and GFCI devices on all appliancecircuits more particularly on outdoors and bathroom locations of outlets.

Most of the secondary wiring systems are grounded for the

following reasons:To prevent a sustained contact between the

low voltage secondary line and the high voltage primary line in case of insulation failure.

To prevent single grounds for being unnoticed or detected until a second ground occurs which could totally disable the secondary line.

To facilitate locating of ground faults.To protect against a short, sudden rush of

electric current in a circuit.To establish a neutral at zero potential for

safety which requires the neutral to: not to be interrupted by switches or other services connect the service entrance to ground only at one

point color coded is necessary for easy identification

CIRCUIT SAFE LOAD

The branch circuit is the technical term for the housewiring installation varies in sizes depending upon the load it is to serve.

I ts is the load refers to the consumption or electricity drawn by lighting fixtures, appliances, equipments.

Conductors sizes for branch circuit is directly proportional to the amount of load it will carry.

NATIONAL ELECTRICALCODE

The Code provides that wiring for electrical circuitry shall be types RHW, T, THW, TW, THWN, XHHW in raceway or cables.

That on a 15 ampere circuit, single appliance should not draw a maximum load of 12 amperes.

That on a 20 ampere circuit, a single appliance shall not draw current in excess of 16 amperes.

That if a branch circuit is combined with lighting or portable appliances, any fixed appliance shall not be allowed to draw more than 7.5 amperes on a 15 ampere circuit and 10 amperes on a 20 amperes circuit.

That on a 30 ampere circuit, a single appliance draw should not exceed 24 amperes.

That heavy duty lamp holders are rated not less than 750 watts.

That, a 30, 40, 50 ampere circuits should not be used for fixed lighting in residences.

That, when loads are connected for long periods, actual load should not exceed 80% of the fuse rating.

That, a continous type load should be considered at 125% of actual load in all load calculations.

That a single receptacle on an individual branch circuit shall have a rating not less than the circuit.

That the number of outlets in a circuit shall be limited to: 6 outlets on a 15 ampere circuit 8 outlets on a 20 ampere circuit

That, receptacles feeding portable and or steady appliance shall be limited to loads of 80% of their rating.That is: 12 amp. For a 15 amp. Receptacle 16 amp. For a 20 amp. Receptacle 24 amp. For a 30 amp. Receptacle

THANK YOU!

FONTE, EDDIE REDBSCE 4-2 / 201112916