Okay, let's break down the complexities of SoCal Edison (SCE) service conductor sizing and address your specific scenario. It's true that SCE's documentation isn't always as readily available or as clear as PGE's.

Understanding the Service Conductor Sizing Rules

The general principle is that service conductors must be sized to carry the calculated load, and they must be protected against overcurrent. However, there are some nuances in the NEC (National Electrical Code) and how POCOs interpret and enforce those rules. NEC 230.42 (Minimum Size and Rating)

This is the core of service conductor sizing. It states that the conductors must have an ampacity not less than the calculated load. This can be the calculated load according to Article 220 (Load Calculations).

NEC 230.90 (Overcurrent Protection)

This section dictates that the service conductors must be protected by an overcurrent device (OCPD).

The "125% Rule"

The NEC often requires sizing conductors at 125% of the continuous load (loads that operate for 3 hours or more). This is common in many applications, but service conductors are not always subject to this requirement.

POCO Requirements (SCE)

This is where things get tricky. SCE can have requirements that go beyond the NEC, as long as those requirements don't violate the NEC. They often have specific rules about minimum conductor sizes for services of particular ampacities.

So, to directly answer your question



You can size service conductors from the meter can to the first disconnect based on their ampacity to carry the calculated load per NEC 230.42 (minimum size and rating), but must be coordinated with the service overcurrent protection device.Your Specific Scenario: 2-4" conduits, 750 KCMIL Aluminum (SCE) to 2-4" conduits 750 KCMIL Copper (Your Work)Here's a breakdown of the possible reasons for the difference in conductor size and how to approach it


SCE's Minimum Requirements

SCE might have a minimum conductor size requirement for a service of a certain ampacity, regardless of the calculated load.

You must verify this with SCE directly. Call their commercial services department or your SCE contact. Ask them specifically about their minimum conductor size requirements for the anticipated service amperage. This is the most likely reason for the discrepancy.2. Voltage Drop

While voltage drop isn't directly related to overcurrent protection, SCE might size their conductors larger to minimize voltage drop, especially on long runs. However, it is unlikely SCE will use a conductor larger than NEC requires for voltage drop.3.

Ampacity Differences (Aluminum vs. Copper)

750 kcmil Copper has a higher ampacity than 750 kcmil Aluminum. Refer to NEC Table 310.16 (and any derating factors) for the specific ampacities based on insulation type and termination temperature ratings (60°C, 75°C, or 90°C). For example, using NEC 310.16 (2020 NEC, typical residential service installation): 750 kcmil Copper (90°C insulation, assuming you can use the 90°C rating based on equipment terminations) = 535 Amps 750 kcmil Aluminum (90°C insulation, assuming you can use the 90°C rating based on equipment terminations) = 475 Amps4.

Paralleling Considerations

When conductors are paralleled, as they are in your 2-4" conduit runs, you must ensure that the conductors are the same length, material, cross-sectional area, insulation type, and terminated in the same manner (NEC 310.10(H)).
5.

Termination Temperature Ratings

Be sure to check the termination temperature ratings of the equipment at both ends (meter can and disconnect). You must use the lowest temperature rating for ampacity calculations. If the terminations are only rated for 75°C, you must use the 75°C ampacity columns in NEC Table 310.16.

How to Proceed


Contact SCE Directly

This is the most important step. Call SCE's commercial services department or your SCE contact. Explain your situation and ask them specifically: "What are your minimum conductor size requirements for a [Amperage] service at this location?" "Do you have any specific requirements or preferences for conductor material (Copper vs. Aluminum) for the service conductors?" "Can you provide any relevant documentation or construction standards that outline your service conductor requirements?"2.

Calculate the Load

Perform a thorough load calculation according to NEC Article 220. This will determine the minimum ampacity required for the service conductors.
3.

Determine OCPD Size

Coordinate with SCE and determine the size of the service overcurrent protection device (e.g., the main breaker in the first disconnect).4.

Verify Ampacity

Ensure that the ampacity of your 750 kcmil Copper conductors (after applying any derating factors) is sufficient to carry the calculated load and is appropriate for the OCPD size.5.

Consider Voltage Drop (If Applicable)

Although not directly related to OCPD, if the run is long, calculate the voltage drop to ensure it is within acceptable limits (typically 3% for the feeder plus 2% for the branch circuit).6.

Document Everything

Keep detailed records of your conversations with SCE, your load calculations, and your conductor sizing calculations. This documentation will be essential for inspections and for resolving any discrepancies.

Important Considerations



NEC is a Minimum

Remember that the NEC provides minimum requirements. SCE can impose stricter requirements.

Local Amendments

Check with the local AHJ (Authority Having Jurisdiction) for any local amendments to the NEC that might affect service conductor sizing.*

Safety: Always prioritize safety and follow best practices when working with electrical systems.By following these steps and communicating effectively with SCE, you can ensure that your service conductors are properly sized and installed, and that your project complies with all applicable codes and regulations. Flag for review