Mandatory Megger Insulation Test for Electrical Installations

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A Megger test is a must for most electrical installations, and requirements for this insulation testing are also detailed in most building codes. A Megger insulation test is meant to test the insulation value of wires. A high value of resistance means that the wire has no breaks along its length. This value is measured in ohms of resistance with 1,000,000 ohms considered as a mega ohm. 


A Megger meter uses a high voltage to get an indication of the resistance value, and most meters that are operated on batteries will generate voltages ranging from a thousand to three thousand volts. Some megohmmeters that use main currents can place voltages as high as 15,000 volts and are more often used for large conductors that may be required to carry high voltage current. In other cases, the megohmmeter is used where equipment is very sensitive. 

While Meggers are the norm for use in electrical installation and repairs, many electrical contractors and electricians opt to use test equipment rental to save them the cost of buying the testers outright especially since they are typically used only 25 percent of the time. A Megger meter needs to be properly calibrated and checked at various intervals so that any results obtained can be true.  Any reading that is greater than 999 Meg indicates a wire that has perfect insulation while any reading below 1 Meg points to a wire with insulation problems. Readings in between these norms is an indicator that the wire can function as required.

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