/power-systems

name: pie-power-systems
version: 1.0.0
description: "Electrical power distribution design for infrastructure: load calculations (NEC 220), conductor sizing (NEC 310.16), transformer/UPS/PDU selection, redundancy architectures (N through 2N+1), DC distribution, and voltage classes 120V-480V. Activates for electrical load calculations, conductor sizing, power equipment selection, data center power design, and redundancy architecture planning."
user-invocable: true
allowed-tools: Read Grep Glob Bash
metadata:
  extensions:
    gsd-skill-creator:
      version: 1
      createdAt: "2026-02-26"
      triggers:
        intents:
          - "load calculation"
          - "conductor sizing"
          - "ampacity"
          - "voltage drop"
          - "transformer"
          - "UPS"
          - "PDU"
          - "power distribution"
          - "NEC"
          - "redundancy"
          - "2N"
          - "N+1"
          - "electrical"
          - "circuit breaker"
          - "480V"
          - "208V"
          - "three-phase"
          - "power factor"
        contexts:
          - "data center power design"
          - "electrical system design"
          - "infrastructure engineering"
          - "power system sizing"
applies_to:
  - skills/physical-infrastructure/**
  - "*.calc"
  - "*.sld"

Power Systems Skill

At a Glance

Design and validate electrical power distribution systems from utility service entrance through rack-level PDUs, covering all voltage classes from 120V single-phase through 480V three-phase.

**Activates on:** InfrastructureRequest type='power', any load calculation, conductor sizing, transformer/UPS/PDU selection, redundancy architecture design.

**Key capabilities:**

• NEC Article 220 load calculations (connected load and optional 220.87 methods)
• NEC Table 310.16 conductor sizing with temperature and conduit fill corrections
• Transformer sizing (kVA, K-factor for non-linear loads, impedance selection)
• UPS selection (online double-conversion, runtime calculation, redundancy modes)
• PDU selection (floor-standing and rack PDU, whip ratings, phase balance)
• Redundancy architectures: N, N+1, 2N, and 2N+1 with topology diagrams
• Voltage classes: 120V, 208V, 240V, 277V, 400V, 480V
• DC distribution patterns: 380V DC bus, 48V telecom, 12V on-board
• Safety: arc flash boundaries, GFCI/GFP requirements, shock thresholds

**Code references:** NEC 220 for load calculations, NEC 310 for conductors, NEC 230 for services — always reference the current locally adopted edition of NFPA 70.

> **ENGINEERING DISCLAIMER:** Electrical system design must be verified by a licensed Professional Engineer or licensed Electrician before installation. Arc flash analysis, fault current calculations, and equipment grounding require site-specific engineering. All work must comply with the locally adopted edition of NFPA 70 (NEC) and applicable OSHA standards. User assumes all responsibility for verification.

**Quick routing:**

• Load calculation needed? Start at [Electrical Load Calculation](#electrical-load-calculation)
• Sizing conductors? Go to [Conductor Sizing](#conductor-sizing)
• Selecting equipment? See [Transformer Sizing](#transformer-sizing), [UPS Systems](#ups-systems), or [PDU Selection](#pdu-selection)
• Designing redundancy? See [Redundancy Architectures](#redundancy-architectures)
• Voltage class selection? See [Voltage Classes and DC Distribution](#voltage-classes-and-dc-distribution)

Electrical Load Calculation

Connected Load Method (NEC 220 General)

Process: sum all equipment nameplate ratings, apply NEC demand factors, add 25% future growth margin.

NEC demand factors reduce calculated load to account for the fact that not all loads operate simultaneously:

**Lighting — NEC Table 220.42:**

• First 3 kVA at 100%
• Next 117 kVA at 35%
• Remainder at 25%

**Receptacles — multi-outlet circuits (>10 kVA):**

• First 10 kVA at 100%
• Remainder at 50%

**Motors — NEC 430.24:**

• Largest motor full-load current x 125%
• All remaining motors at 100%
• HVAC: use larger of heating or cooling load, not both (NEC 220.60)

**Data center calculation (industry practice):** 1. IT load = rack_count x avg_rack_density_kW x diversity_factor (0.7-0.9) 2. UPS losses: 3-8% of IT load (online double-conversion) 3. PDU losses: <2% of IT load 4. Cooling: 15-40% of IT load (depending on target PUE) 5. Lighting and miscellaneous: 3-5% of IT load 6. Total calculated load = sum of all above 7. Design service = total x 1.25 (NEC 230.42 minimum service sizing)

Optional Method (NEC 220.87)

Use for existing facilities with 12+ months of metering data:

• Load = 125% x highest 15-minute demand recorded in past 12 months
• Add 125% of all new loads being installed
• More accurate than connected load method for established facilities
• Preferred when measured data is available — avoids over-sizing

Worked Example: 100-Rack Data Center

| Load Component | Calculation | kW | |----------------|-------------|-----| | IT load | 100 racks x 10 kW x 0.8 diversity | 800 | | UPS losses | 800 kW x 5% | 40 | | PDU losses | 800 kW x 1.5% | 12 | | Cooling (PUE 1.4) | 800 kW x 32% | 256 | | Lighting + misc | 800 kW x 3% | 24 | | **Subtotal** | | **1,132** | | **Design service (x 1.25)** | | **1,415** |

This facility needs approximately 1,415 kW (1,770 kVA at 0.8 PF) service entrance capacity. PUE contribution is the dominant non-IT factor — reducing PUE from 1.4 to 1.2 saves ~160 kW of service capacity.

For full NEC 220 demand factor tables and calculation worksheets: @references/nec-load-calculations.md

Conductor Sizing

Ampacity Tables (NEC Table 310.16)

NEC Table 310.16 provides ampacity for copper conductors in raceway at ambient 30 deg C. The 75 deg C column is standard for most commercial and industrial installations:

| Wire Size | 75 deg C Ampacity | Common Use | |-----------|-------------------|------------| | 12 AWG | 25A | Branch circuits to 20A breaker | | 10 AWG | 35A |