Sub panel feeder circuit sizing

[erichter]

I’m planning to upgrade the service in a detached garage, which is currently fed by a single 15amp circuit, and I wanted to confirm that I have my circuit sizing correct. The existing circuit runs through ¾” IMC buried under the driveway, which I’d like to re-use to run a new feeder circuit to a sub-panel in the garage. Per Table C.1, I can have a maximum number of 4 conductors for 6AWG THWN-2, Table 310.15(B).16, says I can run a maximum of 75amps on 6AWG copper THWN-2, and 310.15(B) states that I do not need to de-rate for 3 or fewer conductors. The rest of the circuit (main load center to buried conduit, then from buried conduit to the sub panel) will be run though 1” PVC conduit. Based on this, I believe I should be able to run a 70 amp breaker for this circuit. Am I correct on the sizing, or am I missing anything?

 

[Little Bill]

I am closing this thread in accordance with forum rules. This forum is intended for use by electricians and electrical contractors, inspectors, engineers, and vendors with their job-related duties. We are not allowed to provide how-to advice to persons who are not employed in this industry, or persons who do not perform electrical installation or maintenance as part of their jobs. Engineers are welcome to participate, but only if their questions do not involve attempts to perform their own electrical installation, troubleshooting, or maintenance work.

If I have misread the situation, if for example you have an electrical contractor on board to perform the installation work, then send me a PM to explain the circumstances.