Temperature limitations for conductors is important concept to understand for the Red Seal Electrical IP exam as this concept is used for large part of the test, especially in wiring methods and motors. When current goes through a conductor and rises in temperature, the insulation encapsulating it must be able to withstand it and not melt.
Insulation temperature is usually indicated in wire type; for example, a NMD90 wire has 90C insulation, a NMD75 has 75C insulation, etc. However, when establishing the temperature limitations in a circuit, it is crucial to consider is equipment termination temperature.
Procedure
Step 1
Is the conductor being used within the first 1.2 m of conductor length, measured from the point of termination on the equipment?
If yes or not indicated in the question, move to Step 2. Otherwise, use the insulation temperature marked on the conductor.
Step 2
Is there a marked termination temperature on equipment within the circuit?
Note #1: Conductors are not classified as equipment.
Note #2: At times, equipment may be marked by two different equipment terminations, for example, 60/75 C. Unless stated explicitly in manufacturer instructors or stated otherwise in the Code, you may use the higher temperature.
Note #3: In particular to circuit breakers, they are marked as 60/75 C termination. Most of the time, you may use 75 C termination temperature, but based on 14-104(2), there may be restrictions on max conductor or amperage for 14 to 10 AWG or 15 A to 30 A.
If yes, use the lowest temperature rating between conductor insulation temperature rating and the equipment’s termination temperature rating. Otherwise, move to Step 3.
Step 3
Is the equipment high voltage?
If yes, establish the equipment’s termination temperature rating through the manufacturer. Otherwise, move to Step 4.
Step 4
Is the conductor a motor supply conductor?
If yes, refer to Rule 28-104(1). Otherwise, move to Step 5.
Step 5
Use Rule 4-006(2) to determine maximum conductor termination temperature where:
a) 60 C for equipment if rated not more than 100 A; or marked for use No. 1 AWG or smaller conductors
b) 75 C for equipment if rated more than 100 A; or marked for use with conductors larger than No. 1 AWG.
Practice Red Seal IP Exam Questions
Example #1
What is the maximum ampacity for a 8 AWG NMD90, terminated on a circuit breaker?
Step 1: Not indicated in the question. Move to Step 2.
Step 2: It isn’t 10 AWG or less so 14-104(2) does not apply. Terminates at 75 C since it is a circuit breaker. Since 75 C is less than 90 C, use 75 C as conductor insulation temperature.
Look up 8 AWG @ 75 C on Table 2 -> 50 A
Example 2
What is the size of RW90XLPE conductors installed in a run of threaded rigid metal conduit for a synchronous motor-generator with a FLA of 26 A?
Minimum Calculated Conductor Amps = 26 x 1.25 = 32.5 A; Rule 28-106(1)
Step 1: Not indicated in the question. Move to Step 2.
Step 2: No marked temperature termination. Move to Step 3.
Step 3: Not high voltage. Move to Step 4.
Step 4: Not motor supply conductor. Move to Step 5.
Step 5: Since 32.5 A < 100 A, use 60 C as conductor insulation temperature.
Look up 32.5 A @ 60 C on Table 2 -> 8 AWG
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