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CLOSE THIS BOOKElectrical Installation - Basic vocational knowledge (Institut fr Berufliche Entwicklung, 201 p.)
8. Testing of installed plants
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENT8.1. Visual inspection
VIEW THE DOCUMENT8.2. Testing the insulation resistance
VIEW THE DOCUMENT8.3. Functional testing

Electrical Installation - Basic vocational knowledge (Institut fr Berufliche Entwicklung, 201 p.)

8. Testing of installed plants

After completion of the electrical plant the supplier of the electrical plant will have to test the installed plant prior to handing over to the customer.

By the tests to be performed on the one hand the expert construction of the plant regarding function and on the other hand its safety will have to be established.

The results are to be laid down in a test certificate if so required by the user of the electrical plant. For each system the following tests are to be undertaken:

- visual inspection,
- ascertaining the insulation resistance,
- functional test

During determining the insulation values and when carrying out the functional test special care will have to be taken. These tests are being performed with a test voltage or the mains voltage applied. There is an increased risk of accident.

8.1. Visual inspection

On visual inspection the overall electrical plant will be checked. This is done in dead condition of the plant.

By means of suitable tools like screw drivers and wrenches as well as by manual testing it will have to be ascertained that

- all distributions, switches, plug arrangements and the other equipment including lines and line fittings are properly fixed;

- all clampings are tightened;

- the pull reliefs at portable electrical equipment are firmly fitted.

By means of drawings and other design documents it is to be checked whether

- the minimum cross sections prescribed have been observed in the installation, e.g. for conductors and potential equalization lines;

- cables, wires and conductors have been properly marked and, where required, special designations have been provided;

- installation materials have been used expertly, the minimum distances and dimensions have been observed;

- connections have been made in the rotational direction of the terminal screws and multicore conductors have been specially prepared;

- automatic cut-outs, releases and fuses have been correctly dimensioned resp. properly set;

- voltage-carrying parts have been properly covered;

- the correct installation materials have been used resp. have been installed at the place provided for in the design.

8.2. Testing the insulation resistance

A sufficiently strong insulation of the electrical plant is required for its operation.

Short-circuits, line-to-earth faults and faults of frame caused by damages may exist in the electrical installation. They are to be traced by testing the insulation resistance.

For that purpose it will be required to remove all fuses and to disconnect all consumer’s installations by unscrewing, disconnecting or pulling out. Switches are, however, to be closed. By applying a test voltage and sampling the conductors against each other as well as against mass or earth the insulation condition of the installation will be established. For generating the test voltage a hand generator or another insulation measuring instrument is being employed.

Fig. 8.1. Hand generator with connected test lines

On a three-phase four-wire network the following tests will have to be performed:

- between conductors L1 and L2
- between conductors L1 and L3
- between conductors L2 and L3
- between conductor L1 and PEN
- between conductor L2 and PEN
- between conductor L3 and PEN.

If the rated voltage of the electrical plant is up to 60 V the test voltage of the insulation measuring device will have to be 500 V.

If the rated voltage of the electrical plant is more than 60 V the test voltage of the insulation measuring device will have to be 1000 V.

Cable and wire installations are to be short-circuited after applying the test voltage!

An insulation value of 10 k Ohm/V in newly installed plants is considered to be sufficient. This minimum value must not fall below.

8.3. Functional testing

Part of functional testing is the current flow test being carried out in dead condition. Current flow testers rendering an optical or acoustic signal on the current flow are almost exclusively operated by torch batteries of 1.5 resp. 4.5 V!

Handling of current flow testers is very simple. By means of two test prods the test voltage will be applied to the conductor of the cable to be tested.

If there is no interruption in the conductor the current flow tester will give an optical or acoustic signal.

If there is no signal, there is an interruption in the conductor or in the plant.

By systematic encircling and searching the fault will have to be found and remedied.

Fig. 8.2. Current flow tester

1 cable (switch line), 2 conductor bridging (switch), 3 test line, 4 current flow tester

After applying the mains voltage the voltage condition of the plant will be established.

For that purpose two-pole voltage testers are employed. During testing the glow lamp will light, warning of the applied voltage. Similarly as in case of the insulation value check, testing by the voltage tester is done subsequently between the phase conductors and then between phase conductors and protective conductor resp. earth. It will be very important to ascertain functioning of the protective measure against too high a contact voltage. Function of neutralization, protective earthing and current-operated earth-leakage protection is being established by a loop measurement (of the protective conductor’s resistance). Also in this case testing is performed in live condition. This measurement is carried out between each phase conductor and the protective conductor. Connecting and disconnecting the measuring lines should, however, take place in dead condition.

Table 8.1. Testing and measuring devices

Current flow tester (bell, buzzer, glow lamp 4,5 V, telephone)

plant to be dead

current flow test

Hand generator

plant to be dead

insulation test

Voltage tester two-pole (load testing button or voltage meter)

plant to be live

functional test ascertaining voltage condition

Phase-sequence indicator

plant to be live

functional test ascertaining sequence of phase conductors

Test plug Loop measuring device

plant to be live

functional test, testing function of protective measure

8.4. Summary

Prior to commissioning the newly erected or expanded electrical plant, three basic testing procedures are to be undertaken:

- Visual inspection

By visual inspection faults are to be found. Test or measuring devices will not be employed.

- Insulation test

Subsequent to visual inspection, insulation testing will be performed. By establishing the insulation capacity proper operation of the electrical plant is to be warranted. Testing devices will be employed.

- Functional test

Functional testing means ascertaining the current flow and the voltage condition. Testing and measuring devices will be employed.