Installation commission and maintenance part 3

Topic includes

- Domestic installation

- How do I I stall wiring

-  Kinds of Electrical installation

- Low voltage switch gear

- Testing and commissioning in Electrical construction work.
- Open circuit test
- Short circuit test
- Polarity test
- Fault localization
- Job cards

What is domestic installation?

House electrical wiring is a process of connecting different accessories for the distribution of electrical energy from the supplier to various appliances and equipment at home like television, lamps, air conditioners, etc. 

How do I install wiring?

Step 1: Disconnect the Power and Install the Boxes.

Step 2: Run the Cable.

Step 3: Prep and Secure the Ground Wires.

Step 4: Splice the Neutral and Hot Wires.

Step 5: Connect the Switches to Each Box.

Step 6: Wire the Fan and Fixture.

Step 7: Wire the Circuit Panel and Finish Installation.

KINDS OF ELECTRICAL INSTALLATION TESTING

Following tests shall be carried out: Wiring continuity test, Insulation resistance test, Earth continuity test, Earth resistivity test, Performance test, and any other tests as instructed by the Supervising Engineer.

1. ELECTRICAL WIRING CONTINUITY TESTING

All wiring system shall be tested for continuity of circuits, short circuits and earthing after wiring is completed and before energizing.

2. ELECTRICAL INSULATION RESISTANCE TESTING

The insulation resistance shall be measured across earth and the whole system of conductors, or any section thereof, with all fuses in place and all switches closed and except in concentric wiring all lamps in position of both poles of the installation otherwise electrically connected together.

3. ELECTRICAL EARTH CONTINUITY PATH TESTING

The earth continuity conductor metallic envelops of cables, shall be tested for electric continuity and the electrical resistance of the same along with the earthing lead but excluding any added resistance or earth leakage circuit breaker measured from the connection with the earth electrode to any point in the earth continuity conductor in the completed installation shall not exceed one ohm.

4. ELECTRICAL TESTING OF NON-LINKED SINGLE POLE SWITCHES

In a two wire installation a test shall be made to verify that all non linked single pole switches have been fitted in the same conductor throughout, and such conductor shall be labeled or marked for connection, throughout, and such conductor shall be labeled or marked for connection to an outer or phase conductor or non earthed conductor a test shall be made three or four wire installation a test shall be made to verify that every non linked single pole switch is fitted in a conductor to one of the outer or phase conductor of the supply. The entire electrical installation shall be subject to the final acceptance of the Supervising engineer as well as the local authorities.

5. ELECTRICAL EARTH RESISTIVITY TESTING

Earth resistivity test shall be carried out in accordance with British Standard Code of Practice of Earthing. All tests shall be carried out in the presence of the Supervising Engineer.

Low voltage switchgear

Low Voltage Switchgear are familiar to every people since they are the controlling mediators between low voltage utilities and equipment with human beings. Be it a common home DB or an isolator or control centres, they all are being manufactured to use untrained people ie., common people. The scope of works shall cover the supply installation, testing and commissioning of main and sub-distribution boards, panel boards, fusible safety switches, circuit breakers etc. Associated minor building works require for the erection of the distribution boards and panels shall be included in the scope of work.

Testing and commissioning in electrical construction work

At the completion of the electrical installation works, the entire installation shall be subject to the test before final placing in service under the full responsibility of the contractor. Unless Otherwise specifically called for all tests shall be carried out in conformity with IEE regulations. Contractor shall coordinate with the Client and the Supervising Engineer to get electricity from the local supply authority before starting of testing and commissioning.

 Open circuit test

The open-circuit test, or no-load test, is one of the methods used in electrical engineering to determine the no-load impedance in the excitation branch of a transformer. The no load is represented by the open circuit, which is represented on the right side of the figure as the “hole” or incomplete part of the circuit.

Method

The secondary of the transformer is left open-circuited. A wattmeter is connected to the primary. An ammeter is connected in series with the primary winding. A voltmeter is optional since the applied voltage is the same as the voltmeter reading. Rated voltage is applied at primary.

If the applied voltage is normal voltage then normal flux will be set up. Since iron loss is a function of applied voltage, normal iron loss will occur. Hence the iron loss is maximum at rated voltage. This maximum iron loss is measured using the wattmeter. Since the impedance of the series winding of the transformer is very small compared to that of the excitation branch, all of the input voltage is dropped across the excitation branch. Thus the wattmeter measures only the iron loss. This test only measures the combined iron losses consisting of the hysteresis loss and the eddy current loss. Although the hysteresis loss is less than the eddy current loss, it is not negligible. The two losses can be separated by driving the transformer from a variable frequency source since the hysteresis loss varies linearly with supply frequency and the eddy current loss varies with the frequency squared.

Since the secondary of the transformer is open, the primary draws only no-load current, which will have some copper loss. This no-load current is very small and because the copper loss in the primary is proportional to the square of this current, it is negligible. There is no copper loss in the secondary because there is no secondary current.

The secondary side of the transformer is left open, so there is no load on the secondary side. Therefore, power is no longer transferred from primary to secondary in this approximation, and negligible current goes through the secondary windings. Since no current passes through the secondary windings, no magnetic field is created, which means zero current is induced on the primary side. This is crucial to the approximation because it allows us to ignore the series impedance since it is assumed that no current passes through this impedance.

The parallel shunt component on the equivalent circuit diagram is used to represent the core losses. These core losses come from the change in the direction of the flux and eddy currents. Eddy current losses are caused by currents induced in the iron due to the alternating flux. In contrast to the parallel shunt component, the series component in the circuit diagram represents the winding losses due to the resistance of the coil windings of the transformer

Short circuit test

The purpose of a short-circuit test is to determine the series branch parameters of the equivalent circuit of a transformer.

Method

The test is conducted on the high-voltage (HV) side of the transformer where the low-voltage (LV) side or the secondary is short circuited. A wattmeter is connected to the primary. An ammeter is connected in series with the primary winding. A voltmeter is optional since the applied voltage is the same as the voltmeter reading. The LV side of the transformer is short circuited. Now with the help of variac applied voltage is slowly increased until the ammeter gives reading equal to the rated current of the HV side. After reaching at rated current of HV side, all three instruments reading (Voltmeter, Ammeter and Watt-meter readings) are recorded. The ammeter reading gives the primary equivalent of full load current IL. As the voltage applied for full load current in short circuit test on transformer is quite small compared to the rated primary voltage of the transformer, the iron losses in transformer can be taken as negligible here.

What is Polarity Testing? 

A test that creates a circuit using the phase conductor and the single pole device in question, breaking the circuit when operating the device, means that the reading on the instrument will change, and thus confirming that that device must be connected in the phase conductor.

Fault localization 

Fault localization is the process of tracing back signals through an integrated circuit to locate the first failing node. This process can be performed using either mechanical probing or electron beam probing.

Job cards 

Cards are a method of production control, making it easier to track and plan throughout the process. There are a variety of cards, the functions of which sometimes overlap depending upon the production and the preferences of the company producing it. Most of us are familiar with the idea of time cards or library slips,these are a decent analogy, but they tend to contain less detail than a job or route card. Cards do not necessarily have to be physical either.

Job cards are a means of tracking what actually takes place in the production process. The job card is created for a single production, and the work and time that goes into that production is then recorded on the card. We might consider the job card to be a demonstration of one or more steps detailed in the route card. This is then used for bookkeeping, payroll, and so forth.


Quite simply, a job card involves time to completion and a route card involves travel of a certain part.

A job card is all about timing.  There are many details involved.  What are the materials used?  What is the time allowed so that production doesn't run over?  What did the current report of inspection say?  These are all things that could be found on a job card.  A business will have the number of job cards that equal exactly the number of operations that are done in that business.