Yes, the ampacity adjustment factors found in Table 310.15(C)(1) (formerly 310.16 in some older NEC editions) of the National Electrical Code (NEC) apply to both AC and DC circuits.Here's a breakdown: Applicability to DC

The NEC does not differentiate between AC and DC for the purpose of ampacity adjustment factors due to bundling. The heating effect, which is the underlying reason for these adjustments, is primarily based on the current flowing through the conductor, regardless of whether it's AC or DC.

Heat Generation

The primary source of heat in a conductor is the current (I) flowing through it and the resistance (R) of the conductor. This is described by the formula: Power (Heat) = I²R.

DC

With DC, the current is constant (or nearly constant in a PV system), so the heat generation is relatively steady.

AC

With AC, the current is alternating, but the effective (RMS) current determines the heat generation. The RMS current is the equivalent DC current that would produce the same heating effect.

Bundle Effect

When conductors are bundled together, the heat generated by each conductor in the bundle contributes to the overall temperature rise of the bundle. This reduces the ability of each conductor to dissipate heat into the surrounding environment, therefore needing a derating adjustment.

Bundle Size

The ampacity adjustment factors in Table 310.15(C)(1) are based on the number of current-carrying conductors in a raceway, cable, or bundle. The more conductors, the greater the derating. This is because the heat from each conductor contributes to the overall temperature of the bundle, making it harder for any individual conductor to dissipate heat.

PV System Considerations

In a PV system, the DC current from the PV array can be substantial, especially in larger systems. The conductors connecting the PV modules to the inverter are subject to the same ampacity adjustment requirements as any other conductors. Therefore, if you bundle multiple DC conductors together (e.g., in a conduit), you must apply the ampacity adjustment factors from Table 310.15(C)(1) (or similar table in your local code).

Key takeaways


Yes, the derating rules for bundled conductors apply equally to both AC and DC circuits.2. Heat is generated by current flow regardless of AC or DC. The heat will affect all conductors in the bundle, causing the necessity to use derating tables for both DC and AC.3. Proper application of these factors is crucial to ensure the safety and longevity of the wiring in your PV system.Example:

Suppose you have four current-carrying DC conductors bundled together in a conduit. According to Table 310.15(C)(1), you might need to derate the ampacity of each conductor to 80% of its listed ampacity. You would then select a conductor size based on the calculated derated ampacity and the continuous current it needs to carry.Always consult the latest version of the NEC (or your local electrical code) and consult with a qualified electrician or PV professional to ensure that your wiring is compliant with all applicable codes and standards. They can help you calculate the correct conductor sizes and apply the appropriate ampacity adjustment factors for your specific installation. Flag for review