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Here's the nameplate from a 5 HP single phase electric motor - used in an air compressor:

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Note that it reads:

HIGH TORQUE GREASE BEACON 325

which I interpret to mean that you should use high temperature grease of which "Beacon 325" is an example or recommended brand / product.

I'm familiar with electric motors which either have used permanently-lubricated sealed or shielded bearings, or alternatively bearings which required oil. But I haven't come across any which require periodic grease maintenance.

Although a permanently sealed bearing would of course have grease I'd be surprised if a motor was expected to be disassembled for regular grease service. And I don't see any grease fittings.

So what does this mean? What service is implied by the grease statement on the label? Could this refer to the motor application (air compressor) and not the motor itself? But it seems like a general purpose motor.

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  • $\begingroup$ Looks to be a general purpose GE motor, some of which require occasional maintenance to re-lubricate parts. If there isn't a grease plate on the motor itself there is probably an access point for grease underneath a removable cover. $\endgroup$
    – jko
    Nov 10 '20 at 14:48
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Grease gets used in roller and ball bearings which are well-sealed to prevent dirt intrusion and which are only rarely disassembled for maintenance (i.e., relubrication). Even when the bearing is hot, the grease does not seep out of the bearing and let it run dry the way that oil would. So (for example) automotive wheel bearings are greased but not oiled.

Oil gets used in bearings where they cannot be well-sealed against dirt intrusion and which use cheap bronze bushings instead of more expensive balls or rollers to carry the bearing loads. In this case, the porous bronze bushing is surrounded by an oil-soaked wick which keeps the gap between the bushing and the shaft running through it wet with oil, which slowly seeps out of that space over time.

So the specification for grease in your case means the bearings contain balls or rollers for long life and high loads, which are intended to be maintenance-free for thousands of hours of operation even in dusty conditions.

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