Okay, Dan, I've reviewed your riser diagram and wiring diagram (E2.0). Here are my thoughts, focusing on accuracy and potential issues

Overall Impressions:

The diagram generally reflects your stated intent of replacing an existing service while maintaining power to the building for as long as possible using a temporary manual transfer switch and the new panel's MCB as a means of disconnect.

Specific Observations and Recommendations



General Clarity

The diagram is generally clear, but some labels could be more precise for less ambiguity.

J-Box Connections

You should be clear that the J-boxes are only being used for wire splicing and not for any disconnects.

Neutral/Ground Connections



Critical Consideration

Double check Neutral and Ground Connections. Confirm if the neutral and ground bars are bonded in

both the existing service and the new service. If so, the neutral/ground bond must be removed from one of the service entrances once the new service is energized and the old service is to be demolished. If left unaddressed a parrallel ground current will exist. CTs and PTs

Ensure the new CTs and PTs have the same ratio and accuracy class as the existing ones. The utility might have specific requirements on these.

Short-Circuit Current Rating (SCCR)

Verify that all components in your new setup (MTS, panel, breakers, J-Boxes, etc.) have an adequate SCCR to handle the available fault current at your service entrance. This is critical for safety and code compliance. You'll likely need a short-circuit study to determine the available fault current.

Wire Sizing

The wire size feeding the load in the J-box, confirm they are properly sized for the 1200A load and voltage drop considerations. Also, consider the parallel conductor requirements in NEC 310.10(H).

Conduit Sizing and Fill

Ensure conduit sizes are adequate for the conductors being pulled through them, considering conduit fill requirements (NEC Chapter 9).

Equipment Grounding Conductors (EGCs)

Ensure EGCs are appropriately sized and connected to all enclosures and equipment.

Labeling

Excellent that you're labeling everything. Ensure the labeling is durable and meets code requirements (e.g., clearly identifying the "Temporary" nature of connections).

Coordination with Utility

Talk to the utility early and often. They will need to approve your plan, provide specific disconnect/reconnect procedures, and might have specific requirements for the CTs/PTs and grounding.

Safety Procedures

Documented safety procedures are critical. Include lock-out/tag-out procedures.

Testing

Plan for thorough testing after each stage (e.g., before connecting the load to the new service) and before demolishing the old service. Testing should include insulation resistance (megger) tests, phase rotation checks, and voltage measurements.

Step-by-step Procedures

Create a detailed, step-by-step procedure for each stage of the process. This will minimize errors and improve safety.

Regarding E2.0 Specifically



"Feed Thru Lugs"

It's good you specified "feed thru lugs" on the new 1200A MCB. Make sure the lugs are rated for the correct wire size and number of conductors.

Key Concerns and Questions



Arc Flash Hazard

Changing out a service of this size presents a significant arc flash hazard. A detailed arc flash hazard assessment is essential. Ensure workers are wearing appropriate PPE, and consider using remote switching or other methods to reduce the risk.

Contingency Plan

Have a contingency plan in place for potential problems during the switchover (e.g., if the new service doesn't work as expected).

Recommendations Before Proceeding


Get Approval

Obtain approval for your plan from the utility, the AHJ (Authority Having Jurisdiction, i.e., your local electrical inspector), and your internal engineering team.2.

Comprehensive Review

Have a qualified electrical engineer thoroughly review your design, diagrams, and procedures.3.

Risk Assessment

Conduct a formal risk assessment to identify potential hazards and develop mitigation strategies.4.

Clear Communication

Maintain clear and open communication with all stakeholders throughout the project.By paying close attention to these details, you can ensure a safe and successful service upgrade.

Disclaimer: I am an AI Chatbot. This information is for general guidance only and should not be considered professional electrical engineering advice. Always consult with qualified professionals for specific project requirements. Flag for review