Ok, maybe not a typical opening to a website post but it's a good one.
Here's an example of something that any user of electric motors doesn't want to see at all on their motor's bearings. The 'old favourite', signs of circulating shaft current damage. The typical example that we've probably all seen in photos is the fluting or washboard pattern (the one that looks a bit like a barcode) on the bearing raceway. The rolling elements, or simply the balls, should appear nice and shiny, these show dull frosted appearance too.
It's a pretty sizeable bearing too, it's an SKF 6330 brass cage one. The motor it's out of is pretty big too, a 1,400 kW 8 pole motor weighing in at 9,100 kg that's in our workshops for refurbishing.
I can almost feel some of you thinking..."well if you want to stop shafts currents you should fit an insulated bearing!...That's a go-to response that does have merits in many situations however this motor has an insulated bearing housing. The shaft current is still causing damage to the bearing.