1990/09/10 Caterpillar

All SR 4 Generators With VR-3 Voltage Regulators And Droop Current Transformers

The wiring connections for the droop shown in the Service Manuals SENR3475, SENR3904, SENR3905 and SENR4794 are incorrect.

When the droop CT (current transformer) is wired as shown in these manuals, the droop circuit will work correctly for the "open frame" CT (7C6979 Transformer Assembly called out in 9Y3857 and 9Y2940 Transformer Groups). But, it will operate backward for the "donut" CT (9Y9437 Transformer Assembly called out in 9Y9439, 9Y9440, 9Y9441, 7E0088, 7E6240, 7E6241, 4P3847 and 4P3848 Transformer Groups). The reason for this is the primary polarity marking on the "open frame" CT is reversed according to standard marking convention. The service manuals diagrams reflect this non-standard marking. The primary polarity mark on the donut CT follows standard marking convention, while the secondary labels were made consistent with the open frame CT. This results in the donut CT wire numbers (5 and 6) being reversed and the secondary wires in the amp connector being reversed as well.

To correct the error do the following:

1. The wire labels on the "open frame" CT wires should be switched so that the wire labeled 5 should be labeled 6, and the wire labeled 6 should be labeled 5. The polarity mark label (1) should also be switched.

2. The wire labels on the "donut" CT wires should be switched so that the white wire is labeled 6 and the black wire is labeled 5. The polarity mark should remain on the white wire. The amp connector should be rewired so that the white wire gets connected to where the black wire was installed and the black wire gets connected where the white wire was installed.

The illustration shows the correct diagram and polarity marking that should be used for reference when working with the droop circuit.

Droop circuit.