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NOTE: This is an unformatted excerpt from our online fire protection training library.

Conductor Selection & Application

Minimum Size to Avoid Overheating Terminals

Three Sizes: An Example

Consider, for example, a 95 amp continuous load. Three sizes must be considered, though not necessarily in this order.

If the load is considered to be continuous, it would have to be increased by 25% to establish the minimum size of the conductor for connection to an overcurrent device. That increase might point to a 125 amp overcurrent device and a 1 AWG conductor that's big enough for 125 amps because the calculated minimum for each is 119 amps. (For a noncontinuous load, the conductor must be sized for 100 percent of the load.) The 1 AWG is chosen from the column that corresponds to the terminal temperature rating of the overcurrent device, in this case, 75° C.
The actual load on the conductor is still only 95 amps, and that would suggest a conductor that only needs to be big enough for 95 amps at the nominal rating. This case, and most cases, would probably require at least a 75° conductor, regardless of terminations. Assuming 75° C conductors with no required corrections or adjustments, this minimum size would be 3 AWG.
Termination temperatures must be considered. In this example, dealing with conductors that may be 1 AWG or smaller, a 60° termination would be assumed on the load or "appliance" end so Section 110.14(C) and Table 310.15(B)(16) would require 2 AWG, because that's the size that appears for a 95 amp load in the 60° column. The 125 amp overcurrent device would allow for the use of the 75° column, but the lower-rated end is the limiting factor.
NOTE: This is an unformatted excerpt from our online fire protection training library.

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