Motor Insulation Ratings

[dwall174]

I recently bought a new/old stock 1/2HP 1725RPM 3-phase motor that I plan to use with a VFD for a small lathe.
The motor has class "F" insulation which I understand is the minimum recommended for a motor running on a VFD.
However, it also shows type F+ on the ID plate!
I've done a ton of searches, but I haven't been able to find out what the "+" mark after the "F" is for?

 

[mm08822]

Agreed, difficult to find and majority of motor nameplates don't mention that parameter.

Best I could find.....
.

 

[RPH]

The biggest problem with using Vfd drives on non-servo motors is cooling it. At slow speeds the fan doesn’t provide the proper air flow. Lots of motors used as low speed units require additional fans for cooling.

 

[dwall174]

The biggest problem with using Vfd drives on non-servo motors is cooling

Yeah, that's probably why it's recommended for a motor running on a VFD to have at least class "F" insulation to help handle the extra heat created at low speeds.

I've seen several motor VFD setups where they do use electric axillary cooling fans for cooling.

 

[Tundra1]

I have no direct knowledge of the + in this case, but what I've seen in transformer insulation rating is the vendor adds a little secret sauce to their insulation type. Then they make it distinct and supposedly a bit better than the competition. It's outside and slightly exceeding the nema rating system. Just a guess though.

 

[dwall174]

Yeah, I'm thinking it may also have sone type of secret sauce or something to do with the wire it's self

I have a 2HP Baldor & a Baldor VFD on my Powermatic 1200HD drill press & the motor has a sticker on it saying that it's wound with inverter spike resistant wire.

Maybe it's something like that?