That's correct. You only use the 125% rule for calculating the minimum required ampacity of the conductor. You do NOT use the 125% factor when correcting or adjusting the already-calculated ampacity for ambient temperature or number of conductors in a raceway.Here's a breakdown to clarify

1. Initial Ampacity Calculation (125% Rule):
This is where the 125% factor comes into play. When determining the minimum ampacity of a conductor, you need to account for continuous loads. Continuous Load

A load expected to operate at its maximum current for 3 hours or more.

Calculation

`Minimum Ampacity = (Non-Continuous Load Amps) + (1.25 Continuous Load Amps)`

2. Ampacity Correction & Adjustment

Once you've determined the minimum required ampacity, you look up the corresponding conductor size from NEC Table 310.16 (or the appropriate table for the wire insulation type). This is the ampacity you find in the table.

Now, you apply correction and adjustment factors to this value. You do not re-apply the 125% factor at this point.Ampacity Correction (Temperature)

If the ambient temperature is higher than the temperature rating used for the table (usually 30°C or 86°F), you must correct the ampacity. You find the correction factor in NEC Table 310.15(B)(1) (or the appropriate table) based on the conductor insulation type and ambient temperature.

Corrected Ampacity = (Table Ampacity) (Correction Factor)

Ampacity Adjustment (Number of Conductors)

If you have more than three current-carrying conductors in a raceway, cable, or earth (or a higher number as defined in 310.15(C)(1)), you must adjust the ampacity. You find the adjustment factor in NEC Table 310.15(C)(1) based on the number of current-carrying conductors.

Adjusted Ampacity = (Corrected Ampacity) (Adjustment Factor)

Important Distinction

The 125% factor is about sizing the conductors initially. Correction and adjustment factors are about ensuring that the conductor's capacity to dissipate heat is not exceeded in the given environment and configuration. You've already accounted for the continuous load when determining the minimum ampacity.

Example


Continuous Load

40 amps2.

Non-Continuous Load

10 amps

Minimum Ampacity Calculation

10 amps + (1.25 40 amps) = 60 amps. You need a conductor with at least 60 amps of ampacity before temperature and conduit fill corrections.3.

Choose Conductor

Let's say you select a conductor that has an ampacity of 65 amps from Table 310.16 (after considering insulation type).
4.

Ambient Temperature

40°C5.

Correction Factor (from Table 310.15(B)(1) for the conductor type)

0.886.

Number of Current-Carrying Conductors

67.

Adjustment Factor (from Table 310.15(C)(1))

0.80

Corrected Ampacity

65 amps 0.88 = 57.2 amps

Adjusted Ampacity

57.2 amps 0.80 = 45.76 ampsIn this example, the final adjusted ampacity is 45.76 amps. This is LESS than the continuous load of 40 amps, so you'd need to go back and use a larger conductor and recalculate. You would

NOT* multiply the 40-amp continuous load by 1.25 again. You only do that once in the initial calculation.Therefore, remember to separate the initial sizing calculation (including the 125% rule) from the correction and adjustment calculations. Flag for review