Let's break down the requirements for a 200A service disconnect in a commercial building

1. The 200A Service Disconnect Itself
Overcurrent Protection is REQUIRED

A 200A service disconnect MUST be protected by overcurrent protection. This is non-negotiable. The National Electrical Code (NEC) requires that service conductors be protected against overcurrent at the point where they receive their supply. This is typically accomplished with a fuse or circuit breaker.

Options



Fused Disconnect

This is a disconnect switch with fuses inline. You'd use fuses rated at 200A or less.

Circuit Breaker Disconnect

This uses a 200A (or less) circuit breaker as the disconnecting means and overcurrent protection.

2. Panel Inside the Building (Downstream of the Disconnect) MLO vs. MCB is your choice, but it depends on the installation. Main Lug Only (MLO) Panel

An MLO panel is fed by the service disconnect (breaker or fused disconnect). It relies on the 200A breaker or fuses in the external service disconnect for overcurrent protection of the service conductors feeding the panel. This is a common and often cost-effective configuration.

Main Circuit Breaker (MCB) Panel

An MCB panel has a main circuit breaker built into it.

In this scenario, the main breaker in the panel must be 200A or less (and sized according to the calculated load), and is typically rated to match the service conductors.Important Considerations and Code References



NEC 230.70(A)(1)

"The service disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors."

NEC 230.91

"Service overcurrent protection shall be provided in each ungrounded service conductor and shall have an ampere rating not higher than the ampacity of the conductor."

NEC 230.90(A)

"Each ungrounded service conductor shall have overload protection." This is the core requirement for overcurrent protection.

Fault Current

Consider the available fault current at the service entrance. The overcurrent protection (fuses or circuit breaker) must have an interrupting rating sufficient to handle the available fault current.

Coordination

If you're using multiple levels of overcurrent protection (e.g., a service disconnect and then breakers within the panel), it's good practice to consider coordination to ensure that the downstream breakers trip before the upstream service disconnect.

Summary and Recommendations


The 200A service disconnect MUST have overcurrent protection (fuses or a breaker).2. MLO or MCB for the panel inside is your choice, but most commonly it's MLO because you already have your protection in the service disconnect. However, if it's an MCB panel you MUST ensure it's rated at 200A or less.3. Always perform a proper load calculation to determine the actual load. This will verify that 200A is the correct service size and allow you to determine proper conductor sizing.4. Consult with the local authority having jurisdiction (AHJ) or a qualified electrical engineer. They have the final say on what is acceptable and code-compliant in your specific location.In short, fuses or a breaker are REQUIRED for your service disconnect. The panel type inside will depend on your design preference, local codes, and load calculations. Flag for review