You're right, Con Edison's ampacity ratings for service conductors often differ from the NEC tables. They have their own engineering standards and take into account factors specific to their system.

Here's a breakdown of what you should consider



Con Edison's Engineering Standards

The first and most important thing to do is try to obtain Con Edison's engineering standards and design guides. These documents will outline their specific requirements for service conductors, including ampacity derating and installation methods. Look for documents related to service design, underground distribution, or building connections. Contacting their engineering department directly is often the best approach.

Why the NEC Tables Don't Directly Apply

The NEC tables are based on general conditions and standardized assumptions. Con Edison's system may have different considerations, such as:

Earth Temperature

Underground conductors in NYC often benefit from stable earth temperatures, leading to higher ampacity ratings.

Conduit Fill

Con Edison might limit the number of conductors in a conduit beyond what's allowed in the NEC, affecting heat dissipation.

Load Diversity

They consider the statistical likelihood of all connected loads operating at their maximum simultaneously.

Future Load Growth

They factor in anticipated future load increases.

Specific Cable Construction

The specific insulation type and construction of the conductors they use may differ, influencing their temperature rating and ampacity.

Safety Factors and System Reliability

They build in safety margins to ensure system reliability and minimize the risk of overloading.

Estimating Ampacity

While I can't give you a definitive answer without Con Edison's documentation, your estimate of

380 amps per 500 kcmil copper conductor is a reasonable starting point. However, don't rely on this for design purposes. Here's why: The NEC 310.16 table shows 380A for 500kcmil copper, assuming 75-degree insulation, 3 conductors in raceway or cable or earth (directly buried). Con Ed likely has factors not covered by the NEC, so the actual rating can be higher or lower. Factors That Might Influence the Actual Ampacity in Con Edison's System



Installation Method

Are the conductors directly buried, in ducts, or in free air?

Depth of Burial (if underground)

Deeper burial often leads to lower temperatures.

Grouping of Conductors

How many sets of conductors are bundled together? More grouping means greater derating.

Soil Thermal Resistivity (if underground)

The type of soil significantly impacts heat dissipation.

Ambient Temperature

The ambient air or earth temperature around the conductors.

Insulation Type and Temperature Rating

XHHW-2, THHN, etc., each have different temperature ratings.*

Best Practices


Consult Con Edison

Contact Con Edison's engineering department or your Con Edison project manager directly. They are the only source for the authoritative answer.2.

Obtain and Review Con Edison Standards

Get their service design standards and any relevant engineering bulletins.3.

Avoid Guesswork

Don't base your design on assumptions. This could lead to undersized conductors and potential code violations or system failures.4.

Documentation

Keep meticulous records of all communications and documentation from Con Edison.5.

Coordination

Coordinate closely with the electrical contractor who will be doing the physical installation, as they will be most familiar with Con Edison's local practices.

In summary, while 380 amps might be a rough estimate, it's crucial to obtain Con Edison's specific requirements to ensure a safe, code-compliant, and reliable electrical service installation in NYC. Using NEC tables alone isn't sufficient. Flag for review