Specialty · Franklin County & St. Louis, MO
Powering a detached garage, a shop, a pool house, or converting from overhead to underground service? CAS Electric handles underground electrical across Franklin County and the Greater St. Louis area — Pacific, Washington, Union, Sullivan, St. Clair, Eureka, Wildwood, Villa Ridge, and Marthasville — proper burial depths, correct conductor sizing, permits, and utility coordination.
Underground electrical looks simple from above ground but there's a lot going on: correct burial depth per NEC 300.5 (depends on voltage, whether it's in conduit, whether it's under concrete, and what type of cable), proper direct-burial or conduit-rated conductors, sweep bends at every direction change, warning tape above the conductor, and correct terminations at both ends. Getting it wrong means a failed inspection or a service call to dig it up in a few years.
Common underground projects for our Franklin County customers: feeder from the main house panel to a detached garage or shop (typically 60–100A sub-panel service), service lateral from Ameren's transformer to a new build or replacement service, buried run to a pool equipment pad or hot tub, low-voltage or line-voltage landscape lighting circuits, and buried feeds to outbuildings, barns, or well pumps.
We handle 811 utility locates, trenching or directional boring coordination, conductor pulling, terminations at both ends, and the permit/inspection. On longer runs we use trenchers or hire a boring contractor; on shorter runs we can hand-trench or use a mini-excavator.
Underground services are quoted per project based on run length, conductor size, and trenching method. We provide a free written estimate after a site visit.
We walk the run, identify obstacles, and design conductor size accounting for voltage drop over the distance.
We call 811 for utility locates and pull the electrical permit before any digging.
Trench to correct depth, install conduit or direct-burial cable, pull conductors, terminate at both ends with correct labeling.
Trench inspected before backfill in most jurisdictions, then closed up, terminations energized, and system tested.
NEC 300.5 depths vary: 24 inches for direct-burial residential branch circuits, 18 inches for PVC conduit, 6 inches for GFCI-protected low-voltage lighting circuits. Under a concrete driveway or slab, 18 inches with 4 inches of concrete cover works. We follow the correct depth for your situation.
Yes — we call 811 before any digging. Ameren, Spire, water, and communications utilities mark their lines within 2–3 business days at no cost. We work around what they mark.
Yes — one of our most common underground jobs. Typical scope is a 60–100A sub-panel in the garage/shop fed from the main house panel via a buried feeder. Includes a disconnect at the outbuilding and separate grounding electrode system per NEC 250.32.
Yes — many homeowners convert overhead services to underground when upgrading a panel or replacing an aging service mast. Requires Ameren approval and a service lateral trench from the transformer, but it's a clean way to remove the overhead drop from the house.
We handle trenching for shorter runs directly. For longer runs or difficult ground (rock, tree roots), we coordinate with a trenching or directional-boring subcontractor.
Licensed, insured, owner-operated. We respond to all estimates within 1 business day.