Okay, let's break down this installation and its code compliance based on the information and pictures provided. The crucial aspect here is whether the 70A tap is compliant and whether the 70A breaker satisfies the panel's overcurrent protection requirements.

Code References (Based on NEC - US National Electrical Code, which I'll assume applies. If you're in a different jurisdiction, the relevant codes may differ.)



NEC 240.21(B) - Feeder Tap Rules

This is the core section governing feeder taps. It outlines the conditions under which you can tap a feeder without full overcurrent protection at the tap point.

NEC 408.36 - Overcurrent Protection

This section mandates overcurrent protection for panelboards, and specifically addresses when a feeder breaker can serve as that protection.

NEC 408.36(A) - Overcurrent Protection

Each panelboard shall be individually protected on the supply side by overcurrent protective devices having a rating not greater than that of the panelboard.

Analysis


Feeder Tap Compliance (Crucial Step)

You must verify the tap conductors meet one of the permitted tap rules in NEC 240.21(B). Common tap rules are:

240.21(B)(1) - 10-foot Tap Rule

The tap conductors must not exceed 10 feet in length, be enclosed in a raceway (or otherwise protected from physical damage), and the ampacity of the tap conductors must not be less than the rating of the device (breaker) they feed and not less than 1/10 of the rating of the OCPD protecting the feeder.

240.21(B)(2) - 25-foot Tap Rule

The tap conductors must not exceed 25 feet in length, be protected from physical damage, and the ampacity of the tap conductors must not be less than 1/3 of the rating of the OCPD protecting the feeder.

240.21(B)(5) - Transformer Feeder Tap

This applies only if there's a transformer involved between the tap and the panel. (Unlikely in your description).

Without knowing the length, ampacity, and physical protection of the tap conductors, it's impossible to definitively say if the tap is code-compliant.2. Panelboard Overcurrent Protection (NEC 408.36)



The Issue

Your Panel HV-1 has a 100A bus rating. NEC 408.36 requires the panel to be protected by an OCPD rated no higher than the bus rating.

Can the 70A Breaker Serve as Protection? Yes, it can serve as the panel's OCPD if and only if the 70A breaker is the first overcurrent device the panelboard sees on the line side. The key is that nothing larger than 100A can feed the panel directly.

Answering Your Specific Question

"Can this 70A branch circuit breaker properly serve as the main OCPD for the panel?"

Yes, IF the 70A breaker is the first and only OCPD protecting the panelboard and the feeder tap rules are followed. It's less than the 100A bus rating of the panel.

Critical Considerations and Things to Check



Tap Conductor Details

Measure the exact length of the tap conductors. Determine their ampacity (based on conductor size and insulation type). Verify they are properly protected from physical damage. These are essential for tap rule compliance.

Tap Rule Compliance

Based on the tap conductor details, explicitly verify which tap rule (if any) is being met. Document this.

Panel Labeling

The panel should be clearly labeled with its busbar rating (100A in this case).

Workmanship

Ensure all connections are properly made and torqued according to the manufacturer's specifications.

AHJ (Authority Having Jurisdiction)

Your local electrical inspector has the final say. Be prepared to justify your installation with code references and calculations.

Feeder Ampacity

Make sure the 300A feeder has appropriate ampacity. Typically requires 3/0 copper or 350kcmil aluminum (check the ampacity table in the NEC).

Practical Experience

While a 70A breaker can theoretically protect a 100A panel, it's often better practice to provide a main breaker closer to the panel's rating. This allows for more flexibility in future circuit additions (within the 100A limit, of course). However, if the load on the panel is consistently low (well below 70A), the 70A breaker might be sufficient.

Recommendations


Prioritize verifying the tap conductor compliance. This is the most likely point of failure.2. Document your calculations and code references. Have them ready for the inspector.3. Consider future needs. If there's a reasonable expectation of needing more than 70A in the future, explore options for increasing the panel's overcurrent protection (which might involve changing the feeder tap or even replacing the panel).4. Consult with a qualified electrical engineer or licensed electrician before making any changes. They can provide tailored advice based on your specific situation and local codes.

In summary, the installation could* be compliant, but only if the feeder tap rules are strictly followed. The 70A breaker is acceptable for protecting the 100A panelboard as long as the tap rules are followed. You need to provide more specific information about the tap conductors to get a definitive answer. Flag for review