Black Fuses

[jwasir]

We have a System, who tripped the main disconnect.

When opened, all the compressor fuses (12) were blown and fuse holder and fuses are blackened by arcing.

We still havn't checked the compressors.

Any suggestions / ideas??

[Brian_UK]

Loose fuses, moisture, fuses pulled when under load.

[scuba]

It sounds like a major arc fault with no fuse cordination. nfpa 70e covers the dangers of an arc fault.

[Magoo]

Could have been caused by a voltage sag/ brown out, definitly check motor windings/ power isolated of course. Meggar test windings to ground and each winding test with ohm meter, with motor leads disconnected at motor.
Alternatively the motor was drawing overcurrent and fuses are under rated and flashed over between phases. Dust and gunge can trigger a flash over, moisture will add to problem.
magoo