How to Make Tests on Installations

a) Insulation tests to earth.

Disconnect the supply by opening the main switch and withdrawing the main fuses.

Insert all fuses at the distribution board (see Fig. 22).

Insert all lamps.

Close all single-pole switches.

Join together the two contacts on the installation side on the main switch, and connect them to one terminal of the Insulation Tester used.

Connect the other terminal of the Tester to the conduit in which the wiring is run or, if lead-covered cable is used, to the lead sheathing. A second connection should also be made to the consumer’s main earth. This second connection is, however, unnecessary if the continuity and earthing of the conduit had been previously tested.

Turn the handle of the Tester at about 160 r.p.m. and take a reading.

In case the result of the test is considered satisfactory the installation is in proper order so far as resistance to earth is concerned.

If, however, the values obtained are not sufficiently high, withdraw all fuses at the distribution fuse board and test again. This test should include only the portion of the installation between the main switch and the busbars of the fuse board.

If the fault is not detected, oneshould proceed to the distributionfuse board and test each branch circuit in turn till the faulty circuit or circuits are discovered. These should be subjected to further tests till the actual fault is detected.

b) Insulation test between conductors.

Remove all lamps.

The main switch should be opened, all fuses inserted at the distribution board, and all single-pole switches in the closed or «on» position.

Connect one terminal of the Insulation Tester to fuse contact and the other to another contact and make a test.

Two readings should be taken on an insulation containing two-way switches, one with both switches on the «on» position and the other with both switches in the «off» position.

If the result of the test between conductors is also satisfactory, no further insulation tests are necessary and the insulation may be considered to be in order.

If, however, the results of the tests are unsatisfactory, proceed to the distribution board, withdraw all fuses and test each branch circuit individually between conductors until the faulty circuit or circuits are located.

What elements should be disconnected, inserted, closed, joined together, connected, etc. for making test on installations?

Read the text and find in it the answers to the questions that follow it.

Contactors Type 370

These contactors consist of the following main parts:

• one fixed bar

• one magnetic circuit which may be either a.c. or d.c.

• one or more auxiliary contacts (the maximum number of auxiliary contacts is 4)

• one or more poles for use with a.c. or d.c. loads.

These components are to be installed.

Their functions are as follows: fixed bar has the function of supporting all the stationary parts of the contactor. At both ends it is provided with holes for mounting the contactor. Moving shaft is made of steel. It is insulated for the installation of both main pole and auxiliary moving contacts.

Fig. 23. Schematic positioning of the different contactor components:

1 - fixed bar; 2 - magnetic circuit: 3 - auxiliary contacts; 4 - poles