I'm wiring my house and would like some feedback on the sizing and routing of conductors between the exterior service entrance and an interior subpanel. On the outside, I have installed a combination service entry device–aka CSED or meter main–by Square D (QC816F200C) with a 200 amp service disconnect. This panel features 8 slots, which will serve a whole-house surge arrestor (SqD HEPD80), a back-up generator power inlet (Eaton EGSPIB30), the well pump, and a branch feeder to power an outbuilding. My plan is to utilize the factory-installed feed-through lugs to then power the house subpanel, located approx. 35' to a central point in the interior. The subpanel is also by Square D (QO130M200PC) and came with a factory-installed 200 amp main breaker. The line between must pass through a sealed and conditioned (but unfinished) crawl space. Can anyone help me size the conductors, and let me know if they must be run in conduit? Many thanks.
Electrical – Powering Subpanel from CSED via Feed-Through Lugs
crawlspaceelectricalsubpanelwiring
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Best Answer
Conduit would be a good idea, even if not strictly required
The main advantage running wires in conduit gives you is that you can put fatter wires, or more wires for something this large even, in if you find that your original run was insufficient. In fact, a 2.5" EMT provides plenty of room for 3 250kcmil aluminum XHHW-2 conductors for now, and even expansion room for 3 more of them should you, or the next bloke who wants this place, want a 400A service later on, in addition to being the obligatory equipment grounding conductor. If EMT is too costly an option, 3" schedule 40 PVC run within the structure could work as well, although you'd then need to run a separate equipment grounding conductor.
If you do go with the cable route, I would go with a 250kcmil-250kcmil-250kcmil aluminum SE-R cable; this gives you the full 200A, but limits you to that all the same.
That's an awfully small subpanel you have there
A 30 space panel is rather on the small side; 42 or even 60 spaces would be a much better use of your money and time here, given that it's far cheaper to buy the spaces now than it is to rip out and replace a too-small panel down the road. Also, you can use a main lug panel on the inside of the house as it's a subpanel in the same structure (so it doesn't need to provide its own disconnecting means) and is not fed by downsized tap conductors (which are protected from overcurrent by the downstream OCPD).