Okay, let's break down this heat trace issue and address your questions. This is a common problem with heat trace, especially on long runs, and it requires a careful analysis of the electrical code and manufacturer specifications.

Understanding the Problem

You're experiencing nuisance tripping due to high inrush current. Heat trace cable, especially self-regulating type, has a significantly higher resistance when warm than when cold. This leads to a large inrush current when first energized, especially in cold temperatures. The longer the cable, the higher the total inrush current. Your measurements confirm this, showing a very high inrush on the water well heat trace and a slightly lower one on the septic system heat trace (which is shorter). The EPD (Equipment Protection Device) breaker is sensitive and designed to trip quickly on overcurrents.

Answers to Your QuestionsQuestion 1: Upsizing Breaker and Branch Circuit Wiring YES, you absolutely MUST upsize the #10 AWG wire if you increase the breaker size to 40 amps. This is a fundamental safety requirement of the National Electrical Code (NEC). NEC 240.4(D)

This section of the NEC specifically addresses the protection of conductors. It states that conductors must be protected against overcurrent in accordance with their ampacity. #10 AWG copper wire, in a typical installation (thermoplastic insulation, 60°C or 75°C rating), has an ampacity of 30 amps. You cannot protect a 30-amp rated wire with a 40-amp breaker. Doing so creates a serious fire hazard.

Upsizing the Wire

To use a 40-amp breaker, you'll need to upgrade the branch circuit wiring to at least #8 AWG copper wire (which has an ampacity of 40 amps at 60C) or larger, depending on the conductor's temperature rating and installation method. Consult the NEC ampacity tables (310.15 and associated tables) for the correct wire size based on insulation type, ambient temperature, and number of conductors in a raceway or cable.

Question 2: Breaker Size: 40A, 45A, or 50A? Start with a thorough calculation

Before increasing the breaker size, you must perform a proper load calculation to determine the minimum required ampacity of the circuit. This calculation will include the continuous load of the heat trace (length in feet 5 watts/foot, divided by voltage, then add a safety factor for continuous load applications) plus any other loads on the circuit.

Raychem's Recommendation

Raychem's advice to not exceed 40 amps is important. While they didn't explicitly prohibit going higher, their testing data stops at 40 amps. This implies they haven't validated the cable's performance and safety beyond that point.

Code Limitations

You cannot exceed the ampacity of the heat trace cable. The NEC requires that overcurrent protection be provided in accordance with the conductor's ampacity.

Potential Solutions (Beyond Breaker Upsizing) Reduce the Inrush Current

Consider using a "soft start" device or inrush current limiter. These devices gradually ramp up the voltage to the heat trace, reducing the initial inrush current. This can allow you to use a smaller breaker.

Staggered Start

If possible, stagger the start-up of the heat trace system. Perhaps the Well and the Septic System can have a 15 minute delay.

Timer Control

Instead of leaving the heat trace on continuously, use a timer to activate it only when temperatures are low enough to warrant freeze protection. This will also save energy.

More Branch Circuits

Break up the total heat trace length into multiple shorter runs, each with its own breaker and wiring. This reduces the inrush current on each circuit.

Example Load Calculation (Illustrative)

Let's assume the well water heat trace is exactly 380 feet long.1. Continuous Load (Watts)

380 feet 5 watts/foot = 1900 watts2.

Continuous Load (Amps)

1900 watts / 208 volts = 9.13 amps3.

Continuous Load (Ampacity Requirement)

Because heat trace is considered a continuous load, you must increase the calculated load by 25%. 9.13 amps 1.25 = 11.41 amps.This calculation shows that the minimum ampacity required for the circuit is 11.41 amps based on the continuous load. The problem isn't the continuous load; it's the inrush current.

Recommendations1. Prioritize Safety

Upgrading the wire is non-negotiable if you increase the breaker size.2.

Inrush Current Limiting

Before considering a 45A or 50A breaker (which I strongly advise against), thoroughly investigate inrush current limiting devices. This is the safest and most code-compliant approach.3.

Consult a Qualified Electrical Engineer

Given the complexity of this situation, the potential safety hazards, and code requirements, it's highly recommended that you consult with a qualified electrical engineer. They can perform a detailed load calculation, evaluate the existing system, and recommend the best solution to address the inrush current issue while ensuring safety and code compliance.4.

NEC Compliance

Ensure that all work complies with the current edition of the National Electrical Code (NEC) as adopted by your local jurisdiction.

Important Considerations EPD Breaker Sensitivity

EPD breakers are designed to protect equipment. If the problem is nuisance tripping due to inrush, a standard breaker might be more appropriate if you can safely limit the inrush current. An engineer can help assess this.

Voltage Drop

On long runs of wire, voltage drop can be a concern. Ensure that voltage drop is within acceptable limits according to the NEC.

Ground Fault Protection

Ensure that the ground fault protection is properly sized and functioning.

Documentation

Keep detailed records of all calculations, decisions, and changes made to the system.

In summary: Don't simply upsize the breaker without addressing the underlying inrush current issue. It's a band-aid solution that can create a significant fire hazard. Focus on limiting the inrush current, using appropriate wiring and overcurrent protection, and consulting with a qualified electrical professional. Flag for review