Medium Voltage Motor Conductor Temperature rating

[elmatador]

Hi there

We have several 4000v 3000HP motors which are fed from a Siemens MCC FVNR cells. My understanding is that medium voltage equipment is suitable for 90degC terminations where the ampacity of the conductor can be based on 90deg ampacities. How about the motor end? These are API 541 motors with class f insulation and b temperature rise. Is there anywhere in any specification that mentions the rating associated with the motor. Since the motor is above 500HP it doesn't have a NEMA MG-1 Design code. I did read in places where design codes B,C,D,E requires 75deg terminations.

Any feedback on this subject would be greatly appreciated. I am following the Canadian Electrical Code on this.

 

[waross]

28-104 Motor supply conductor insulation temperature rating and ampacity
(1) Supply conductors to a motor connection box shall have an insulation temperature rating equal to or
greater than that required by Table 37, unless the motor is marked otherwise and their ampacity is based
on a 75 °C conductor insulation rating except for Class A rated motors only, where their ampacity shall
be permitted to be based on a 90 °C insulation rating, when 90 °C wire is used as circuit conductors to
the motor.
(2) Where Table 37 requires insulation temperature ratings in excess of 75 °C, the motor supply conductors
shall be not less than 1.2 m long and shall terminate in a location not less than 600 mm from any part of
the motor except that for motors rated 100 hp or larger, their terminations shall be not less than 1.2 m
from any part of the motor.
(3) For ambients higher than 30 °C, the supply conductor insulation rating shall be increased at least by the
difference between the ambient and 30 °C.

Table 37
Motor supply conductor insulation
minimum temperature rating, °C (based
on an ambient temperature of 30 °C)
(See Rule 28-104.)

Motor enclosure
Insulation class rating
A B F H
All except totally enclosed
non-ventilated
75 75 90 110
Totally enclosed
non-ventilated
75 90 110 110



Bill
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"Why not the best?"
Jimmy Carter