Service Entrance & Capacity
~12 min read · Read service size from conductors and equipment, and verify drop/lateral clearances.
The service is the house's electrical front door: drop or lateral, mast and meter, and the capacity question every buyer asks — how many amps? The inspector reads conductor size, panel rating, and clearances without ever touching a live part.
Drop, lateral, and clearances
Overhead service drop: utility conductors to the mast/weatherhead — inspect for tree contact, abraded insulation, and clearance PRINCIPLES: high above walking surfaces, higher above driveways and roads, safely clear of windows, decks, and pools (exact figures are utility/code territory; the finding is conductors reachable from a deck or scraping a maple). Underground lateral: check the meter base and visible riser conduit for damage and sealing. Drip loops at the weatherhead keep water out of the mast; a mast pulled loose or a rotted mast board is a structural service finding.
- Tree contact and abrasion on drops
- Reachable-from-deck/window conductors = the clearance finding
- Drip loop, weatherhead, and mast integrity
Reading service capacity
Capacity is the SMALLEST of: service conductor ampacity, panel bus rating (the label), and main breaker/fuse rating. Field reading: main breaker handle (100/150/200 A), panel label, and conductor gauge where visible (rough conventions: modern 100 A copper ≈ #4, 200 A copper ≈ 2/0; aluminum runs larger). Legacy red flags: 60-amp services (often fused, undersized for modern loads), cloth-insulated conductors, and meter equipment from the same era. Report capacity as observed and note when it appears marginal for the home's size and equipment (electric ranges, dryers, EV chargers, heat pumps).
- Capacity = the weakest link: conductors, bus, main
- 60-A fused services: upgrade-conversation finding
- Match capacity against modern load expectations
Meter and grounding interface
At the meter/service equipment: rust or water in the meter base and service equipment (water follows service conduits downhill into panels — look for staining below the entry), sealed and secure fittings, and the grounding electrode conductor leaving the service toward rods/water pipe (its condition and connections belong to the grounding lesson). The utility side is outside the SOP — the inspector observes and reports; only the utility opens their equipment.
Worked example
A 1962 ranch with a listing claim of '200-amp service': the service drop passes through a silver maple and sags within arm's reach of the new rear deck's rail; the main panel's breaker reads 100 A on a bus labeled 125 A; visible service-entrance copper looks like #4; and the meter base shows rust streaks with matching water stains inside the panel below. Reconcile and report.
Capacity: the weakest link rules — #4 copper and a 100-A main on a 125-A bus make this a 100-amp service regardless of the listing (report the discrepancy neutrally: observed equipment indicates 100 A). The maple: branch contact abrades insulation and loads the drop — utility/trimming referral. The deck reach: conductors graspable from the rail are a serious clearance/safety finding — built after the service, the deck created the hazard; refer for utility/electrician correction. The water: rust in the meter base and stains inside the panel mean the service conduit is piping rain into live equipment — sealing/correction plus panel-interior evaluation. Four findings, none requiring a single measurement of voltage.
Common exam pitfalls
Reporting capacity from the listing or the biggest number visible.
The SMALLEST of conductors, bus, and main governs — a 200-A panel on 100-A conductors is a 100-A service.
Ignoring what new construction did to old clearances.
Decks, additions, and pools built under existing drops create reachable-conductor hazards — check the relationship, not just the wire.
Missing the water path.
Rusty meter bases and stained panel interiors mark water traveling the conduit — a live-equipment moisture finding.
Weakest link names the amps; trees, decks, and water are the drop's three enemies.
Recap
- Drop: tree contact, abrasion, clearance principles, drip loop
- Capacity = min(conductors, bus label, main rating)
- 60-A and cloth-conductor services: era findings
- Water follows conduits into panels — read the rust
- Deck/pool/addition proximity creates new hazards
- Utility equipment observed, never opened
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