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Measuring Resistance to Electrical Insulation onboard Cargo Ship

Good insulation resistance is essential to the correct operation of electrical equipment. A means must be available therefore to measure insulation resistance. Readings taken regularly will give an indication as to when and where corrective action, maintenance, servicing, etc., is required.

Insulation resistance may be measured between a conductor and earth or between conductors. Dirt or other deposits on surfaces can reduce insulation resistance and cause a leakage current or 'tracking' to occur. Equipment must therefore be kept clean in order to ensure high values, in megohms, of insulation resistance.

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Insulation is classified in relation to the maximum temperature at which it is safe for the equipment or cables to operate. Classes A (55 degC), E (70°C) and B (80°C) are used for marine equipment.

One instrument used for insulation testing is shown in Figure . Its trade name is 'Megger Tester'. A permanent magnet provides a magnetic field for a pivoted core which is wound with two coils. A needle or pointer is pivoted at the centre of rotation of the coils and moves when they do. The two coils are wound at right angles to each other and connected in such a way that one measures voltage and the other measures current.

Electrical insulation tester

Fig: Electrical insulation tester

The needle deflection is a result of the opposing effects of the two coils which gives a reading of insulation resistance. A hand driven generator provides a test voltage to operate the instrument. Test probes are used to measure the resistance at the desired points.


Explosive gases may be inadvertently ignited by electrical machinery such as The probability of the ignition of explosive gas by electrical machinery may be reduced by:



Related Info:

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