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I have a 400-amp service to a house with 2 200-amp breakers for disconnects. The 2 200-amp sub panels are in the interior of the house with a concrete slab floor. Does the sub panel feeder have to be in conduit or just buried 18 inches using direct burial service feeders?
Thanks for the question. Based on the information provided, the feeders from the service equipment to the panelboards (sub panels) inside the home, should be installed using a suitable direct burial wiring method (Direct burial rated MC Cable) in accordance with Exception No. 2 to Section 300.5(C) and 330.10(A)(5). It is important to remember the general rule here in 300.5(C) is to installed conductors and cable in raceways under buildings. From a practical and workmanship standpoint, conductors or cable in a raceway allows accessibility for reworking them or repairs and so forth that may be necessary later. With a direct buried cable, if something were to go wrong, it would likely need to be abandoned and a new feeder rerouted overhead. Just thoughts based on your question. Hope this is useful.
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