75°C Ampacity of 200°C Wire

[jtinge]

I have an application where a user wants to use a high power, water cooled motor for research applications. The motor is feed by high temperature motor wiring having an insulation rating of 200°C to handle the large current and reduce conductor size due to space limitations. This will have to be connected to VFD equipment that will have 75°C terminals.

My thought is to connect the motor leads to 200°C rated terminals. From the terminals feed (unknown qty) parallel sets of the same size 200°C wire (or larger size (?) 200°C wire) to the VFD such that the ampacity of the 200°C wire connected to the VFD is not greater than the 75°C ampacity of the wire, and thus can be connected to 75°C terminals of the VFD.

Several questions:
1. Assuming a 30°C ambient, how do you determine the 75°C ampacity of the 200°C wire?

2. Is there a better way to connect the high temperature motor conductors to 75°C rated terminals?

 

[kingpb]

Why not just use the ampacities in the NEC for 75degC based on the AWG size of your 200degC conductor between your 200degC termial block and VFD.

 

[jtinge]

Good point. This is a high flexibility wire, but could use the ampacity for the same size and stranding 75°C wire as the 200°C wire. Thanks.

 

[publicgood]

Derate the 75c wire based on 200c.

 

[kwired]

Is your 200C conductor copper or is it nickel or some other metal/alloy?

T310.15(16) will be fine if copper or aluminum. 75C column is what you want to use for 75C terminations even if you have more then 75C insulation.

Add: there is T310.15(18) that has higher temp and nickel conductors in it - but keep in mind the ampacities in that table are for more then 75C so can't apply to a 75C terminal.