The attached photo is a hot joint on a 3phase motor isolator, the reason for the failure is that an incorrect lug (copper) was used to terminate an aluminium cable. As you can see in the photo the other two lugs under the tape are much larger, these are bi-metallic lugs.
I was recently reading an article on Crimp Lugs used in electrical installations and apparently this particular problem is the most common cause of cable/connector failure, next to using the wrong sized connector. Looks like this particular crimp lug has just corroded and burned away because of the higher resistance connection. This could have been a nasty failure had it gone un-noticed.
It requires the isolator to be replaced and white Ø cable extended and re terminated to new islolator switch to remedie this fault properly.
Same here too the Al cable needs enough surface area in the lug to have a low resistance connection between cable and lug
I have found it here many times too in distribution pillars and transformers. Wrong lugs used to terminate to busbar or NZI fuses in transformers. or Cu droppers made to connect bimettalic lugs to and not enough surface area between lug and dropper causing hot spots.
The bimetalic lugs also rely on the surface area between lug and terminal to allowe for a low resistance surface hence the larger size of the eye.
Seen many times that solid Al 70 mm² cables just been srewed straight into HRC fuse carriers without any transition joint or joint compound used.
The product of rotation, excitation and flux produces electricty.
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