The figure which explains the Additive type polarity is shown in the figure below. If V3 reads voltage as the difference of both V1 and V2 then, it is as subtractive type. The polarity of the primary winding and the secondary winding is the same.
The terminals A1 and A2 have the same polarity whereas B1 and B2 have the same polarity. The figure which explains the subtractive type polarity is shown in the figure below. Apparatus required for the practical testing of the transformer are auto-transformer, voltmeters, and a transformer. Practically connect the primary winding of the transformer to an auto-transformer. The practical working figure of a polarity test on the transformer is shown in the figure below. Polarity check of lighting circuit is done by using a Megger.
While using megger, check its working condition by shorting both the probes of megger it denotes zero resistance as it is shorted.
The internal resistance of the winding should be high in the case of proper working. For Testing Lighting circuit, connect one probe to the one end of the bulb and the other probe is connected to the Line with switch SW kept open. If the switch SW is ON, then the pointer of megger shows less resistance value.
From this, we can conclude that the polarity of the lighting circuit is correct. Before performing insulation resistance test between installation and earth the conditions to be fulfilled for the position of the main switch, fuses, switches, and other points should be as under For testing the whole installation, the test is conducted on the main switch. A testing set known as megger is used for the test. It is a special form of the ohmmeter.
To perform this test, the phase and the neutral is short-circuited temporarily at any suitable point as shown in Figure. The handle of the tester is turned at a high speed so that sufficient testing voltage is produced.
The reading on the dial of the megger is noted. The insulation resistance thus measured should not be less than 0. If the insulation resistance is below this value, the wiring section giving that value should be rewired or checked thoroughly until the required value is obtained.
To ensure that the insulation of the cables or wires is not damaged and there is no leakage between them, this test is performed. Before performing this test, the position of the main switch, fuses, switches, etc. The line terminal of the megger is connected to phase terminal of the installation and the earth terminal of megger is connected to neutral wire.
These tests and other practical guidance have been provided to assist electrical practitioners to achieve safe, compliant and competent electrical work, and to promote continued improvements in those areas.
Electron newsletter Date published: 6 December About us. This is a live test so extra care is advised! Step 1. Select a GS 38 approved voltage indicator and locate the Main Switch.
Test between Line and Neutral terminals. Step 2. Test between Line and Earth terminals.
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