You're right to be concerned; this is a massive code violation and a significant fire hazard. Here's a breakdown of why and what likely happened, and what needs to be done

Why This Is Wrong (and Dangerous)
Overcurrent Protection

#12 AWG copper wire is typically rated for a maximum of 20 amps (check the insulation type for specifics, but 20A is a common limit). A 600A breaker should only trip if 600 amps or more are flowing through the conductor it protects. A #12 wire will melt and likely cause a fire long before a 600A breaker trips. It offers absolutely NO protection for that smaller wire.

NEC Violation

The National Electrical Code (NEC) dictates that overcurrent protection (circuit breakers or fuses) must be sized to protect the conductors they serve. This situation is a clear violation. You can't connect a wire rated for 20 amps to a breaker 30 times larger than its capacity.

Fire Hazard

As mentioned, the most likely outcome of an overload or short circuit on the #12 wire is that it will overheat, melt its insulation, and potentially start a fire. The 600A breaker won't trip in time to prevent this.

Possible Tampering

This suggests someone may have tampered with the equipment

What Likely Happened (Possible Scenarios)

It's hard to say exactly what someone was thinking, but here are some common (though incorrect) reasons people do this:1. Lack of Understanding of Overcurrent Protection

The person who installed this may not have understood the fundamental principle of overcurrent protection – that the breaker's job is to protect the wires, not the equipment at the end of the circuit.2.

Tapping for Convenience

Someone needed to power something on those floors and thought it was easiest to tap off the main service disconnect. They might have thought, "Well, it's a big breaker, so it can handle it."3.

Misunderstanding of Transformer Purpose (Less Likely Here)

If there were transformers involved (and it's possible in a high-rise), someone might have incorrectly thought the transformer was somehow providing the overcurrent protection. However, in this case, it's a service disconnect, so transformers are less likely to be the immediate cause of confusion.4.

Previous Work Not Completed Correctly

Perhaps, previous work was started but not completed correctly, leaving the wiring in a hazardous state.

Why the Configuration Every 3 Floors? Powering each floor. May be for emergency systems?What Needs to Be Done IMMEDIATELY1. Document Thoroughly

Take detailed pictures, note the location of each instance of this issue (which floors), and write down everything you observed. Your documentation could be crucial later.2.

Report to the Authority Having Jurisdiction (AHJ)

This is typically your local electrical inspector or building department. They have the authority to enforce the NEC and ensure the building is safe. Do not delay in reporting this. Explain the situation clearly, providing your documentation.3.

Immediate Disconnection

If possible and safe, immediately disconnect the #12 wires from the 600A breakers. Tag them clearly with a warning "DO NOT CONNECT - UNSAFE". If you can't disconnect them safely, make sure the building management is aware of the immediate hazard and that the affected areas are closely monitored.4.

Licensed Electrician/Engineer Assessment

A qualified and licensed electrical contractor or engineer must evaluate the entire system. They need to determine: The actual downstream loads for each tapped circuit. The correct wire size required for those loads. Whether the existing 600A breakers are appropriately sized for the overall service. A safe and code-compliant solution to provide power to the loads on each floor.5.

Corrective Action

The electrical contractor/engineer will need to design and install a proper solution. This will likely involve: Installing properly sized circuit breakers to protect the #12 wires (probably 15A or 20A breakers). Potentially installing a subpanel with appropriately sized breakers on each floor. Ensuring all wiring is done in accordance with the NEC.6.

Follow Up

After the corrective work is completed, ensure that the AHJ inspects and approves the changes.

Important Considerations Liability

The building owner/manager has a significant liability issue here. They are responsible for the safety of their tenants and visitors. This situation creates a serious risk of injury or death.

Insurance

The building's insurance policy may be voided if this condition is discovered and not corrected.

Don't Attempt a DIY Fix: This is not a DIY situation. Improper wiring can be deadly. Only qualified electricians should perform this work.In summary, this is a critical safety issue that needs immediate attention. Report it to the authorities, ensure the building management is aware, and get a qualified electrical professional involved as soon as possible. Flag for review