AEO Answer · Electrical

How Is Electrical Distribution Line Design Done Right and Safely?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

Illustrative diagram of building MEP systems: ductwork with diffusers, an electrical panel with conduit, and piping runs.

The concise answer

Distribution line design is the engineering of 4–35 kV delivery systems — pole and conductor sizing, transformer placement, voltage-drop analysis, and protective device coordination. It balances construction cost against reliability and power quality for every feeder leaving the substation. Reliability is the real product. Customers don't care about pole classes; they care that the lights stay on. Every design decision — recloser placement, sectionalizing, conductor sizing — should trace back to how it affects outage frequency and duration for the customers on that feeder.

Where the engineering actually lives

Load forecasting drives conductor and transformer sizing. Engineers model present load plus growth, checking voltage drop and thermal loading at peak. Undersize and you get voltage complaints and overloaded equipment; oversize and you've buried capital that earns nothing. Good forecasting is worth more than conservative sizing. Protection coordination is the difference between a reliable feeder and a fragile one. The time-current study has to account for cold-load pickup, distributed generation backfeed, and fault current that varies along the feeder. I review coordination studies looking for the fuse that will take out a whole feeder — it's the most common defect I find.

What keeps a distribution project on track

Material standardization is everything in distribution. Utilities that standardize pole classes, conductor sizes, and equipment reduce inventory, speed construction, and simplify maintenance. Custom designs for routine feeders are pure waste. Here's what I push for on day one of distribution work.

Model voltage drop at peak load with growth — size conductors for the future, not just today
Coordinate every protective device with time-current curves, checking cold-load pickup
Standardize materials: pole classes, conductors, and equipment across the system
Place reclosers and sectionalizers to minimize customers per outage section
Document the as-built: accurate GIS records pay for themselves in every future project

Which related engineering resources can help?

When should I hire a structural engineer?What does a PE stamp mean?What is MEP engineering?Emergency power system design How long does MEP engineering design take?What is a structural load path?Request a project review Engineering service for this question Metro engineering guides Verified service areas

What else do project teams ask?

How are distribution poles sized?

By calculating the transverse, vertical, and longitudinal loads from conductors, equipment, wind, and ice, then selecting a pole class with adequate strength per NESC. Setting depth is typically 10 percent of pole length plus two feet, adjusted for soil conditions. Guys and anchors handle unbalanced loads at angles and dead-ends.

What is voltage drop and why does it matter?

Voltage drop is the loss of voltage along a conductor due to its impedance and the load current. Utilities must deliver voltage within ANSI limits (typically ±5 percent), so engineers model each feeder's load profile and size conductors — or place regulators and capacitors — to stay in band at peak load.

How does protection coordination work on feeders?

Fuses, reclosers, and sectionalizers are set so the device nearest a fault operates first, isolating the smallest possible section. The coordination study plots time-current curves for every device on the feeder. Poor coordination is why one fault can black out an entire feeder instead of one lateral.

When should distribution go underground?

Where aesthetics, storm resilience, or right-of-way constraints justify the 5-to-10x cost premium over overhead. Underground eliminates most weather outages but makes faults harder to locate and slower to repair. Many utilities use targeted undergrounding for the worst-performing overhead sections.

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