Mike Dolt Enterprises
Mike Dolt Enterprises
User: T DeNault, Location: New York
Asked on: Saturday, March 29, 2025 at 10:07 am EDT
Answered on: Saturday, March 29, 2025 at 10:28 am EDT
Question: Hello ladies and gentlemen, I have a 20 KW Geo Thermal unit which is roughly 60' from the service equipment. I have an abundance of 1/0 AL SER left over from installing sub Panels throughout the project. I would Like to use this wire for a sub panel feeder for the 20 KW Geo Thermal unit, which would have three 240 volt circuits on #6 copper on a 2 pole 50 Amp circuit breaker. The 1/0 Al will be on a 100 Amp Circuit breaker and the wire is good for 120 Amps with the 20 KW at a maximum of 84 Amps with 125% it is 105 Amps. My question is, Is the 1/0 AL SER and 100 Amp Circuit breaker that's protecting it code compliant to run the 20 KW Geo Thermal Unit. Thank you for your time and Knowledge.
Okay, let's break this down to determine if your plan is code-compliant. I'll refer to the National Electrical Code (NEC) – assuming that's what your area follows.
Here's a breakdown of the key considerations
Load Calculation
Geothermal Unit Maximum Current
You've correctly identified that 20 kW at 240V, and with the 125% multiplier, results in a calculated load of 105 amps.2.
Ampacity of 1/0 Aluminum SER
90°C Rating
1/0 Aluminum SER is typically rated for 90°C in the conductor, which is what we need to use for calculating the ampacity of the wire. Based on Table 310.16, 1/0 Aluminum (90°C) has an ampacity of
120 amps.3. Overcurrent Protection
100 Amp Breaker
You propose protecting the 1/0 Aluminum SER with a 100 amp breaker.
Code Compliance Analysis
Wire Ampacity vs. Load
The 1/0 Aluminum SER has an ampacity of 120 amps. The calculated load is 105 amps. The wire is adequately sized for the load.
Overcurrent Protection vs. Wire Ampacity
The 100 amp breaker is below the wire's 120 amp ampacity. This is compliant.
Overcurrent Protection vs. Load
The 100 amp breaker is below the calculated load of 105 amps. This is not compliant. The maximum overcurrent protection shall not exceed the conductor.
Based on the analysis above, the 1/0 Aluminum SER and 100 amp Circuit breaker is NOT code compliant to run the 20 KW Geo Thermal Unit.Recommendations
Increase Overcurrent Protection
Increase the size of the breaker. You need to have a breaker that can handle the 105 amp load. Since the wire is rated to 120 amps, you would need to replace the 100 amp breaker for a 110 amp breaker, assuming there is one, or a 120 amp breaker.
Important Considerations and Caveats
Local Amendments
Local jurisdictions may have amendments to the NEC that could impact these calculations. Always check with your local building department or a qualified electrical inspector to confirm compliance with local codes.*
Voltage Drop
While the wire is sized for the current, voltage drop can be a concern over a 60-foot run. Calculate the voltage drop to ensure it remains within acceptable limits (typically 3% for feeders). I can help you with this calculation if you provide more details.
Disclaimer: I am an AI Chatbot. This information is for general guidance only and should not be considered a substitute for the advice of a qualified electrician. Electrical work can be dangerous, and it's essential to consult with a professional to ensure safety and code compliance. Flag for review