Data Center Power Distribution Design
Design power distribution for a small data center — transformer sizing, UPS, PDU layout, and redundancy calculations.
Scenario Overview
Design the power distribution for a 200 kW IT load data center with 2N redundancy, including transformer, UPS, and PDU sizing. This is a Tier II facility with a single utility feed and UPS backup.
Given Information
- •IT load: 200 kW (planned maximum)
- •Redundancy: 2N UPS, N+1 cooling
- •Utility feed: 480V, 3-phase from building main
- •IT voltage: 208Y/120V for server racks
- •PUE target: 1.4 (total facility power/IT load)
- •Generator backup: yes, 10s transfer
Calculation Steps
Determine Total Facility Power
PUE = Total Facility Power / IT Load.
Total = 200 kW × 1.4 PUE = 280 kW.
Non-IT loads (cooling, lighting, losses): 280 − 200 = 80 kW.
Result: 280 kW total facility power
Size Main Transformer
Total: 280 kW at approximately 0.90 PF = 311 kVA.
Select next standard size: 500 kVA, 480V to 208Y/120V.
This provides 64% loading — excellent for efficiency and growth.
Secondary FLA: 500,000 / (208 × √3) = 1,388A.
Result: 500 kVA transformer (64% loaded)
Size UPS System (2N Redundancy)
2N means two independent UPS systems, each sized to carry 100% of IT load.
Each UPS: 200 kW at 0.90 PF = 222 kVA minimum.
Select: 2× 250 kVA UPS units (each at 89% loading).
Battery runtime: 10 minutes minimum (bridging to generator start).
Result: 2× 250 kVA UPS units (2N redundancy)
PDU Distribution
200 kW across standard 42U racks: approximately 5-8 kW per rack.
25-40 racks at 5-8 kW each.
PDU: whip-style 30A or 50A, 208V PDUs to each rack.
Main PDU panels: 2× 400A, 208Y/120V panels (one per UPS output).
Result: 2× 400A PDU panels, 25-40 rack PDUs
Generator Sizing
Total facility: 280 kW.
Generator sizing: 280 kW / 0.80 loading = 350 kW minimum.
Motor starting factor: HVAC compressors may need 2× starting kVA.
Select: 500 kW diesel generator (provides growth headroom).
Fuel: NEC 700.12(B)(2) requires 2 hours minimum; NFPA 110 recommends 24-48 hours.
Result: 500 kW diesel generator
Final Answer
200 kW IT data center with 2N UPS (2× 250 kVA), 500 kVA transformer (480 to 208Y/120V), 500 kW generator, and 2× 400A PDU panels. Total facility power: 280 kW at PUE 1.4. Full redundancy from UPS to rack PDU.
Key Takeaways
- •PUE accounts for ALL facility power — cooling is typically 30-40% of non-IT load
- •2N redundancy means each UPS must carry 100% of load independently
- •Transformers for data centers should be K-13 or K-20 rated for harmonic loads
- •Generator must account for motor starting surge of HVAC compressors
Calculators Used
NEC References
- NEC 645 — Information Technology Equipment
- NEC 700/701 — Emergency/Standby Systems
- NEC 450 — Transformers
- TIA-942 — Data Center Standards