Distribution Systems

Part of Power Transmission

Designing the network that delivers power from a central generator to individual buildings in a community.

Why This Matters

Generating electricity is only half the problem. Getting that electricity to where it is needed — across a village, through a building, to the specific workbench or lamp or motor — requires a distribution system. Without thoughtful distribution design, power is available only adjacent to the generator, circuits are overloaded or inefficient, and faults in one part of the system knock out everything else.

Distribution system design is fundamentally about matching supply characteristics (voltage, current capacity, AC or DC) to load requirements, minimizing losses in the distribution network, and maintaining safety throughout. The decisions made when designing the initial distribution infrastructure are difficult to change later — laying wires, setting poles, and choosing voltage levels are long-term commitments.

A well-designed distribution system serves a community for decades. It accommodates load growth without complete rebuilding, isolates faults so only the affected circuit is disrupted, and maintains standard voltages at every connection point regardless of what other loads are drawing simultaneously.

Fundamental Architecture

Every distribution system has the same basic hierarchy:

Generation → Step-up → Transmission → Step-down → Distribution → Service entrance → Building wiring

For a small community:

• Generation: One or more generators at a central location (water wheel, wind turbine, diesel)
• Step-up: If the generator output is low voltage (12V, 24V, 48V), a transformer raises voltage for efficient transmission
• Transmission: High-voltage overhead or buried cable running from the generator to the community
• Step-down: Transformer at the community center or at each cluster of buildings reducing voltage to usable levels
• Distribution: Wiring running from the step-down transformer to each building
• Service entrance: The point where community distribution connects to building wiring
• Building wiring: Individual circuits inside each building

Voltage Selection

The first and most consequential decision is choosing system voltage. This affects everything downstream: transformer ratios, wire gauges, component ratings, and safety requirements.

12V DC: The simplest system. No AC safety concerns, compatible with car batteries and solar charge controllers. Severe limitation: high current for any significant power. 1,000W at 12V requires 83A — extremely heavy wire for even modest distances. Suitable only for very small systems (single building, under 500W, runs under 20m).

24V DC: Better than 12V but same limitations apply. Current halved for same power. Compatible with common 24V battery banks and solar inverter stacks.

48V DC: The practical maximum for serious DC systems. Common in telecom, large solar, and industrial DC installations. 1,000W at 48V requires only 21A — manageable for moderate distances. Many modern inverters and charge controllers support 48V.

120V or 240V AC (single phase): Standard residential distribution voltages. 1,000W at 240V is only 4.2A — very practical for distribution runs. Requires transformers, AC generators, safety knowledge. This is the correct choice for any system serving multiple buildings.

400V or 480V AC (three phase): Industrial standard. Efficient for long-distance transmission and for powering motors. Most salvaged industrial equipment expects three-phase. Requires a three-phase generator or transformer bank.

Recommendation for community grid: Use 240V AC single-phase if only one or two buildings, or if three-phase generation is unavailable. Use 400V three-phase for any system serving more than four buildings, or where significant motor loads (workshops, pumps) are present.

Radial vs Ring Distribution

Radial Distribution

The simplest topology: power flows one way, from the source toward the loads. Each feeder branch serves a cluster of buildings.

Source ─── Feeder A ─── Building 1
                    └── Building 2
       ─── Feeder B ─── Building 3
                    └── Building 4

Advantages: Simple to design, easy to understand, cheap to build. Disadvantage: A fault on any feeder interrupts power to all buildings downstream on that feeder.

Use case: Small communities (under 20 buildings) where a few minutes of outage during fault repair is acceptable.

Ring Distribution

Each feeder is a loop — power can reach any building from two directions. A fault on any segment can be isolated while maintaining supply to all other buildings.

Source ─── Ring feeder ─── Building 1 ─── Building 2 ─── Building 3 ─── (back to source)

Advantages: Any single-point fault can be isolated without complete outage to any building. Disadvantages: More conductor required (the ring return path), more complex switching, potential for circulating currents if generator voltage phases are not precisely matched.

Use case: Communities where continuous power to critical buildings (medical, food storage, water pumping) is essential.

Meshed Networks

Multiple interconnections between ring and radial feeders. Highest reliability, highest complexity. Appropriate for mature communities with multiple generators and significant electrical infrastructure.

Feeder Sizing

Each feeder must carry the maximum coincident load of all buildings it serves. “Coincident load” is not the sum of all possible loads — people do not use everything simultaneously. Typical coincident demand factor is 40–70% of connected capacity for residential loads.

Feeder capacity required = Sum of building loads × Diversity factor × Safety margin

Diversity factor: 0.5 for similar-use residential buildings
Safety margin: 1.25 (25% headroom for growth and starting surges)

Example: Four buildings, each with 2kW connected load:
  Maximum coincident demand = 4 × 2,000 × 0.5 = 4,000W
  With safety margin: 4,000 × 1.25 = 5,000W feeder capacity
  At 240V: 5,000/240 = 21A → 6 AWG copper wire minimum

Transformer Placement Strategy

Central transformer (one step-down for all buildings): Simple, but all buildings share one transformer. Failure of the transformer loses power to everyone. Long distribution runs at lower voltage increase line losses.

Distributed transformers (one per cluster): Higher reliability, shorter distribution runs, but more transformers to maintain. Each transformer can be sized precisely for its cluster’s load.

Single-building transformers (service entrance transformers): Each building has its own small transformer. Maximum isolation — one building’s transformer failure never affects another. More expensive in total transformer capacity, but excellent for critical buildings.

Practical compromise: Use a central transformer for most buildings on a common cluster. Add separate service transformers for critical buildings (medical facility, food storage, communications) that must never lose power together.

Three-Phase vs Single-Phase Distribution

Single-phase: Two conductors (hot + neutral). Suitable for residential loads. Unbalanced across phases if only part of a three-phase generator output is used.

Split-phase (US standard): Three conductors from center-tapped transformer secondary. Hot A (120V), neutral (0V), Hot B (120V). Allows 120V single-phase loads (most household) and 240V loads (heavy motors, heating). Excellent for mixed residential/light industrial loads.

Three-phase four-wire: Three hot conductors + neutral. European standard 400V three-phase distribution. Each hot is 230V to neutral; 400V hot-to-hot. Motors and heavy loads use all three phases; light loads use single phase. Most efficient system for large communities.

Generator matching: Build distribution to match what your generator produces. A single-coil AC generator produces single-phase. A three-coil generator (coils 120° apart) produces three-phase. Re-wiring the distribution system to match a different generator is expensive; better to plan the distribution to match the generation from the start.

Power Factor and Reactive Loads

Inductive loads (motors, transformers, fluorescent ballasts) draw more current than their actual power consumption suggests. The ratio of real power (watts) to apparent power (volt-amps) is the power factor. A motor with 0.8 power factor draws 25% more current than a purely resistive load of the same wattage.

This excess current flows through your distribution system, causing additional line losses without delivering useful work. In community-scale systems, the effect is significant:

Correction: Capacitors connected in parallel with inductive loads cancel the reactive current component. Salvaged capacitors from power factor correction panels (found in industrial buildings) can be deployed at the distribution feeder level to improve overall system efficiency by 5–15% in motor-heavy applications.

Load Growth Planning

Whatever distribution capacity you install today will feel insufficient within a few years. Plan for growth:

• Design feeder routes with enough physical space for additional conductors
• Oversize conduit and ducting to allow future wire pulls
• Install transformers with 50% headroom above current maximum load
• Install all switches and protection devices rated for the ultimate planned capacity, even if loads today are modest
• Document everything — future maintainers must understand what you built

The cost of slightly larger wire gauges and transformer capacity at installation time is small compared to the cost of rebuilding a distribution system a few years later.