any thoughts

[Farmelectrics]

carrying out a eicr and noticed on a couple of twin and earth cables entering fuse spurs that there is slight burning marks discoluring of the white twin and earth cable made a note of this in comments circuts tested ok good readings and tightened terminals which were ok anyway so were does this discoulring come from

 

[Richard Burns]

Possibly dirt and not burning, or maybe the FCUs were bad and someone just replaced the FCUs without replacing a slightly marked but OK cable?

 

[Farmelectrics]

richard they were definately burn marks or discoulring not dirt just scratchin head to were they or how they come from