Caterpillar — To Determine Proper Phase Rotation (Using Three Light Bulbs)
Testing & diagnosis · Generator Leads
From a Caterpillar owner's manual covering: 7C-1000, 9Y-1300, 9Y-1400, SR4. Check it applies to your exact model before use.
Applies to: Caterpillar SR4
Before you start
- Never attempt to work on electrically hot wiring. Stop the electric set before rewiring generator leads. Open circuit breakers or remove fuses before working on the equipment which they control.
Procedure
- Connect the light bulbs, with rated voltage, between the generator leads and the corresponding line phase, across the open circuit breaker.
- Start the units to be paralleled and bring them up to speed; as they approach the same speed the lights will start to blink.
- If the lights blink in sequence one of the units is connected backward; remove generator leads 1 and 3 at the circuit breaker and exchange them.
- If lights blink in unison the phase rotation of both generators is the same.
Tools required
- Three light bulbs Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Source: Caterpillar owner's 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.