# Experimental determination of motor properties

There's a motor that I need to seek a replacement for but unfortunately the nameplate is no longer on it and it's been rewound already. While I can spec a new motor for the application, I'd consider this an academic exercise and I'd like to know if there's any way I can experimentally determine the following properties:

1. FLA
2. Insulation Resistance Class
3. Efficiency
4. Number of motor poles

The motor itself is 480V, 3ph and 50HP

Number of motor poles

Get a tachometer and measure the RPM. Assuming 60 Hz line frequency:

• 2 poles / 1 pair of poles = 3,600 RPM
• 4 poles / 2 pairs of poles = 1,800 RPM
• 6 poles / 3 pairs of poles = 1,200 RPM
• 8 poles / 4 pairs of poles = 900 RPM
• 10 poles / 5 pairs of poles = 720 RPM
• 12 poles / 6 pairs of poles = 600 RPM
• 16 poles / 8 pairs of poles = 450 RPM

Efficiency

You'll need a dynamometer to plot efficiency vs torque. Not sure it's worth the effort. Once you do, how is that going to help you? It's not like you won't pick a replacement because it has better efficiency, you know?