Okay, let's break down this electrical panel scenario to ensure you're compliant with electrical codes and best practices. It's important to consult the NEC (National Electrical Code) or your local electrical code as the final authority, but I can provide some guidance.

The Problem

You have a 100-amp overcurrent protection device (OCPD) feeding a power distribution block (PDB). The PDB feeds a busbar, and that busbar then distributes power to five 10-amp OCPDs. Your question revolves around the sizing of the conductors between the PDB and the busbar.

Analysis


Feeder Size and Overcurrent Protection

Your main feeder is protected at 100 amps. This means that any conductors connected directly to the 100-amp feeder circuit breaker must be rated to carry 100 amps. This is the primary issue.2.

Demand on the Busbar

You have five 10-amp circuits connected to the busbar, which means the maximum potential load on the busbar is 50 amps (5 circuits 10 amps/circuit). However, the NEC and good design practices dictate that the conductor feeding that busbar must be rated to carry the maximum available current from the source before the busbar.3.

Conductor Ampacity (NEC Table 310.16)

#6 AWG copper conductors, depending on the insulation type (THHN, THWN, etc.) and installation method (conduit, free air, etc.), typically have an ampacity rating of around 55 amps or more at 75C, which often meets the requirements for the conductors, however, NEC 240.4 (B) could affect your answer based on the next standard size breaker.
4.

The Potential Danger

Without overcurrent protection at the busbar, you could potentially overload the #6 AWG conductors if more than 50 amps of load are applied.

NEC Considerations and Solutions



NEC 240.21 Feeder Tap Rules

The length of the tap conductor is not described in the problem statement. If the tap conductor from the PDB to the busbar is short, there may be exceptions according to the tap rules, but that is unlikely in this application.

NEC 240.3(D) Conductor Overcurrent Protection This section may apply to your panel, in which if the #6 AWG conductors are used to tap the PDB to the busbar and the ampacity of the #6 AWG conductor does not correspond to the standard ratings of fuses and circuit breakers as listed in NEC 240.6(A), then the next higher standard OCPD size can be used. Using a 50-amp or 60-amp breaker may be an option. NEC 408.36 Overcurrent Protection

This section is about switchboards and panelboards. It basically states that the overcurrent device must be located at the point where the conductor receives its supply, unless an exception applies. Since the conductors are run from the PDB to the busbar, these requirements must be met.

Recommendations


Best Practice: Add Overcurrent Protection

The most conservative and code-compliant approach is to add an overcurrent protection device (OCPD) between the PDB and the busbar. A 50-amp OCPD would be suitable and could prevent overloading of the conductors and busbar. The placement must be physically close to where the smaller wire is tapped.2.

Increase Conductor Size

Instead of adding a 50-amp OCPD, you could use a conductor size large enough to handle the 100 amps from the PDB to the busbar. In this case, a #3 AWG copper wire would satisfy this requirement, provided the terminations can accept this size wire.

Important Considerations



Load Calculations

A proper load calculation should be performed for the entire panel. This will determine the actual demand on the busbar and the size of the required conductors. It's possible that your actual load is significantly less than the maximum potential load, but you still need to design for a reasonable safety margin.

Ambient Temperature

High ambient temperatures can reduce the ampacity of conductors. You may need to adjust the conductor size accordingly.

Termination Ratings

Ensure that all terminals (PDB, OCPD, busbar) are rated for the conductor size and the expected current.

Professional Consultation

Always consult with a qualified electrician or electrical engineer to ensure your installation meets all applicable codes and safety standards. This is especially important for electrical panel modifications.
In conclusion

While #6 AWG conductors might be sufficient for the 50-amp load on the busbar, it is best to install a 50-amp OCPD at the busbar to prevent overloading the conductors, or run #3 conductors from the PDB to the busbar to accommodate the entire load of 100 amps. The safest and most NEC-compliant option is to add a 50-amp OCPD between the PDB and the busbar, as this will provide proper protection to the conductors and the busbar.

Disclaimer: I am an AI chatbot and cannot provide professional electrical advice. This information is for general guidance only. Consult a qualified electrician or electrical engineer for your specific situation.* Flag for review