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Home›Repair guides›Marathon›Insulation Resistance Check

Marathon — Insulation Resistance Check

Maintenance · Main stator, main rotor, exciter stator, exciter rotor

From a Marathon service manual covering: 250FDR1000, 250FDR1004, 252FDR1008, 252FDR1012, 252FDR1016, 340FDR1020, 340FDR1024, 342FDR1028, 342FDR1032. Check it applies to your exact model before use.

Before you start

  • Disconnect voltage regulator before megohmmeter or high-potential testing.

Procedure

  1. Disconnect voltage regulator and control/monitoring accessories before any megohmmeter or high-potential test.
  2. Main Stator: connect all stator leads together; measure resistance from leads to stator frame.
  3. Main Rotor: disconnect the 2 rotor leads from the rectifier assembly, connect them together, measure to shaft.
  4. Exciter Stator: connect the 2 leads together; measure resistance between leads and bracket.
  5. Exciter Rotor: disconnect the 3 rotor leads from rectifier, connect together, measure to shaft.

Tools required

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • 1.5 megohm minimum

Source: Marathon service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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