I agree with the division between NFPA outside the motor and NEMA MG-1 for T-leads. I presume the question referred to T-leads.
It’s all a bit confusing to me.
Here’s all that NEMA MG-1 says about the subject:
NEMA MG-1 (2009)
12.43 TEMPERATURE RISE FOR MEDIUM SINGLE-PHASE AND POLYPHASE INDUCTION
MOTORS
The temperature rise said:
for each of the various parts of the motor[/b] shall not exceed the values given in the following table when tested in accordance with the rating, except that for motors having a service factor greater than 1.0, the temperature rise shall not exceed the values given in the following table when tested at the service factor load....
Note I have bolded “for each of the various parts of the motor”, which under conservative interpretation (but not the only interpretation) might include T-leads and (coil knuckles and series jumpers etc....even though there is no mention of measuring temperature of anything other average temperature of entire winding by resistance and and slot temperature by RTD).
Continuing a conservative approach based on the above, if the motor has class F insulation, then the T-leads must be rated at least class F and should be sized so as not to exceed a total temperature of 40C (motor ambient) plus 105C (class F rise) = 155C at rated load for SF 1.0 motor. It should be important to notice that even though the motor ambient is 40C, the T-lead ambient is higher and so I would expect that needs to be considered in sizing the table (cannot pretend the T-lead itself is in 40C ambient by a conservative approach)
However, this is not the only interpretation. Apparently EASA does not interpret it so conservatively.
EASA Tech Manual section 7.2 gives ampacity of leadwire as a function of leadwire rating and size. The same chart is also available here:
I tried to correlate the table to the various NEC tables and was not successful. The ratio between EASA ampacity and NEC table ampacity was not constant.
For example consider 90C cable insulation rating:
NEC Table 310.16 Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 60_C Through
90_C (140_F Through 194_F), Not More Than Three Current-Carrying Conductors in Raceway, Cable,
or Earth (Directly Buried), Based on Ambient Temperature of 30_C (86_F) gives the following ampacites (90C):
18AWG – 14A
1/0 – 170A
The EASA table gives the following (90C):
18AWG – 18A
1/0 – 155A
So on this comparison, the EASA gives more ampacity than that particular NEC table for the 18AWG, but less for the 1/0. I cannot deduce the pattern or logic.
There is also a note at the bottom of the table “Note: Lead wire sizes for ampere ratings in this table represent recommended minimums. It is best to use the lead wire size originally specified by the motor manufacturer.”
A good caveat, I’m sure.
Then there is another table in section 7.2 that suggests
Class B motor must use 90C lead wire
Class F motor must use 125C lead wire
Class H motor must use 150C lead wire.
And an accompanying note: “Note: The thermal class rating for an electrical insulation system need not
include the lead wire as a primary component. Rather, the lead wire may be considered a secondary component of the system, and hence may have a lower temperature rating as a component than the rating of the insulation system.”
So, it appears EASA’s interpretation is that the T-lead wire insulation need not meet the temperature insulation rating of the motor (they did not follow the conservative interpretation I suggested above). However of course the actual cable sizing should consider the actual cable temperature ratings, so it is not non-conservative in that respect. EASA doesn’t mention anything about ambient temperature of the cable itself. Perhaps the ampacity tables they provided have some empirical correction for that somehow. Also worthwhile to note that T-leads are relatively short, so the approaches we use for long cables may not apply.
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(2B)+(2B)' ?