You're right to be concerned and to question the initial plan's allowance of NM cable in the walls. Your interpretation of the red ink note on the plans is also correct, and it strongly suggests Article 518 applies. Here's a breakdown of why, how Article 518 applies, and what you need to do

When Does Article 518 Apply?

Article 518 of the NEC (National Electrical Code) covers "Places of Assembly." It applies to buildings or portions of buildings used for the gathering together of 50 or more persons for deliberation, worship, entertainment, eating, drinking, amusement, or awaiting transportation. This is a critical threshold. If the occupant load is 50 or more, Article 518 kicks in.

Why Your Situation Likely Requires Article 518 Compliance



Occupant Load

The red ink on the approved plans clearly states an occupant load of over 100 people. This definitely triggers Article 518. The note emphasizes that the final occupant load determination could trigger other code requirements for the electrical, mechanical, and plumbing systems.

Restaurant Use

Restaurants fall under the "eating, drinking" category of places of assembly as described in Article 518.

Impact of Article 518 on Wiring Methods

Article 518 significantly restricts the use of NM cable. Here's why the original plan needs re-evaluation:

518.4 Wiring Methods

This section usually requires wiring methods in places of assembly to be installed in metal raceways, Type MC cable, or be part of a manufactured wiring system. NM cable (Romex) is generally not permitted concealed within walls unless specifically permitted by other exceptions (which are unlikely to apply in your scenario).

Fire Safety

The rationale behind this is to enhance fire safety in areas where large groups of people gather. Metal raceways or MC cable offer better protection against fire propagation than NM cable.

How an Electrician is to Know This


Plans and Specifications

The first and most crucial step is to thoroughly review the approved plans and specifications. The plans should state the intended use of the building and often will include a notation of the designed occupancy load.2.

Occupancy Load Calculations

If the plans are silent on occupancy load, it's the electrician's (or often the architect's or engineer's) responsibility to determine the occupancy load based on the building's use and the area available for occupants. Table 220.12 of the NEC provides occupancy load factors (square feet per person) for different building types. In the case of a restaurant with tables, the load factor is typically in the range of 15 sq ft per person.
3.

Consult with the Authority Having Jurisdiction (AHJ)

If there's any doubt, the electrician must consult with the local building inspector or electrical inspector (the AHJ). The AHJ has the final say on code interpretation and enforcement. This is especially critical when the plans seem contradictory or unclear.4.

Continuing Education

Electricians are required to take continuing education courses to stay up-to-date on the latest NEC requirements.5.

Licensed Electrical Engineer

In cases where the occupant load is close to 50 or the requirements are complex, it's highly advisable to consult with a licensed electrical engineer. They can perform the necessary calculations, interpret the code, and design the electrical system to meet all applicable requirements.

What You Need to Do Now


Immediately Raise the Issue

Don't proceed with the NM cable installation. Explain to your boss the potential code violation and the safety implications. This needs to be addressed before any further wiring is done. Document this conversation.2.

Official Confirmation

Get written confirmation from the AHJ regarding whether Article 518 applies based on the approved occupant load. This will remove any ambiguity.3.

Revise the Plans

If Article 518 applies, the plans must be revised to specify appropriate wiring methods (EMT, MC cable, etc.) for the areas covered by Article 518. This may require the services of an electrical engineer and resubmission of the plans to the city.
4.

Occupancy Load Mitigation

Investigate with the building owner if there is an option to reduce the occupant load. For example, can tables be moved or a section be closed off for large parties?5.

Change Order

Prepare a change order for the additional cost of using approved wiring methods. The contractor is responsible for code compliance, and the owner is responsible for paying for it.

Consequences of Non-Compliance



Failed Inspection

The electrical inspection will fail, and the restaurant won't be able to open until the wiring is corrected.

Liability

In the event of a fire, non-compliant wiring can create significant legal liability for the contractor, the building owner, and potentially even the architect/engineer if they failed to properly specify the wiring.*

Safety

Most importantly, non-compliant wiring puts the public at risk.

In summary, the red ink notation about the occupant load over 100, in conjunction with the fact that this is a restaurant, almost certainly means Article 518 applies. NM cable is very likely not permitted concealed in the walls. You need to stop the current installation, get official clarification from the AHJ, and revise the plans to comply with the code. Flag for review