Now that’s a pair of balls!


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.

If anyone gives you the stock answer of..."Well just fit an insulated bearing, that'll stop it!" might just be getting a 'sales' response. Shaft current and bearing damage is a science, it's something that takes a lot of understanding and experience, there's never usually a simple fix. I don't fully understand all there is to know and all the differing things that you can do to mitigate them. There are experts out there though to help.

If you have motors that suffer from repeated bearing damage from shaft currents, you're not alone. If you have this problem, if no one else can help, and if you can find him...maybe you can hire the A-Team!....I mean Richard Thompson He's a guy that knows more about shaft current issues than anyone else I know and here's his email -


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