440/220V low insulation troubleshooting on main switchboard

Could you share an effective method for troubleshooting 440/220V low insulation on the main switchboard ?

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First of all it is necessary to mention that low insulation problems must be identified and attended ASAP. Accumulated low insulation problems are far more difficult to resolve.

This being mentioned, the most efficient way to identify the cause of the low insulation is to isolate all loads, confirm insulation reading is infinite and then reconnect the loads one by one, checking the insulation meter after each reconnection. If the insulation drops after connecting a load it means that the load has problem and needs inspection. Disconnect again that load before continue reconnecting the rest.
Keep in mind that in 440V insulation troubleshooting you need to start investigation by changing generator as a first step. If the low insulation issue is on the generator side then the insulation will drop once the ACB closes (Generator connected to 440V bus). If the low insulation issue is resolved when a generator ACB is opened then the circuit between ACB and alternator needs to be inspected.


Thank you @LamprosJO - very informative response!