Okay, let's break down these scenarios. It's crucial to prioritize safety and code compliance, so I'll provide a detailed analysis. Always consult with a qualified electrical engineer and local authorities having jurisdiction (AHJ) before making any changes to your electrical system. This response is for informational purposes only and should not be taken as professional engineering advice.

Scenario 1: 250ft, 350MCM Cable, 800A Breaker with 600A Plug Cable Ampacity

A 350 MCM copper cable (assuming it's copper and the most common insulation like THHN/THWN) typically has an ampacity of around 310 amps in free air and 310 amps when installed per 310.16, Table 310.16 of the NEC. This is a critical figure.

Overcurrent Protection Rule

NEC Article 240.4(B) states that you can go up to the next standard size overcurrent device for the cable if the conductor ampacity does not correspond to a standard breaker size, only if the load is non-continuous.

Analysis


Mismatched Protection

An 800A breaker, even with a 600A sensor, is

NOT appropriately protecting a 350 MCM cable with an ampacity of roughly 310A (assuming copper and typical insulation). Even though you will be setting the trip settings to trip at 300A, with a 600A sensor, the breaker might not respond quickly enough to protect the cable in a fault condition.2. Digitrip Setting

While you can set the Digitrip 1150 to trip at 300A, that doesn't fundamentally solve the problem of the 600A sensor. The sensor is the limiting factor in how quickly the breaker will respond to an overcurrent. The trip unit then provides the time delay functions of how quickly it trips when there is a certain overcurrent percentage.3.

Possible Solutions



Replace the Sensor/Plug

This is the

best and safest solution. Install a sensor that is closer to the cable's ampacity. A 300A or 400A sensor would be a much better match. Re-evaluate the Load

Is the actual load significantly less than 300A? If so, consider a smaller breaker and sensor combination, perhaps a 400A breaker with a 300A sensor.

Re-Cable

If increasing the cable size is feasible, consider running a larger conductor that can handle the 600A setting. This is likely more costly.

Scenario 2: 1000ft, 500MCM Cable, 200A Load, 800A Breaker with 600A Plug Cable Ampacity

A 500 MCM copper cable (again, assuming copper and common insulation) typically has an ampacity of around 380-430 amps, depending on the installation conditions and insulation type.

Voltage Drop

At 1000ft, voltage drop will definitely be a consideration for a 200A load. Make sure your 500 MCM cable choice will keep the voltage drop within acceptable limits (typically 3-5% max).

Overcurrent Protection

The 200A load has a 200A main breaker.

Analysis


Initial Concern - Breaker is not appropriately sized

The 800A breaker with the 600A sensor is too high for the load. If the load has a fault, the 600A sensor will take too long to trip.2.

Voltage Drop Check

Before proceeding, calculate the voltage drop for your specific installation details (voltage, load characteristics, cable type, installation method). Voltage drop is calculated from the load back to the source. If you have a 200A breaker at the load, the 200A needs to be taken into consideration when sizing the voltage drop.3.

Solutions



Replace Sensor/Plug

You need to ensure the sensor is rated to a lower amperage, such as 300A, and then set the trip settings to 200A.

Feeder Breaker Size

If the 600A is the lowest sensor plug, I recommend looking for a breaker in the 400A range.

Consider a Step-Down Transformer

It would be more appropriate to use a step-down transformer. A step-down transformer would allow a closer protection to the 200A load.

Key Considerations and Recommendations



Selective Coordination

When replacing switchgear, consider selective coordination. This means that the downstream breakers should trip before the upstream breaker in the event of a fault. Ensure your breaker settings and sensors are chosen to achieve this.

Short-Circuit Study

A short-circuit study is essential. It will determine the available fault current at various points in your system and help you select appropriate interrupting ratings for your breakers and verify their coordination.

Ground Fault Protection

Ensure your new switchgear has appropriate ground fault protection. This is crucial for safety and code compliance.

NEC Compliance

Always refer to the latest version of the National Electrical Code (NEC) and any applicable local codes for specific requirements.

Manufacturer's Instructions

Follow the manufacturer's instructions for the switchgear and breaker settings.*

Arc Flash Hazard Analysis

Consider performing an arc flash hazard analysis to determine the potential arc flash risk at your new switchgear and implement appropriate safety measures.

In summary, you need to prioritize cable protection and ensure that the breakers trip quickly enough in the event of a fault. Replacing the sensors/plugs with appropriately sized ones is the safest and most reliable solution. Carefully consider voltage drop for the 1000ft run, and always consult with a qualified electrical engineer to verify your calculations and ensure compliance with all applicable codes and standards. Flag for review