415 V vs. 480 V Data Center Distribution

Key takeaways

• A 415 V design distributes 415Y/240 V to the rack and feeds servers 240 V directly, so the PDU transformers of a 480 V / 208 V design disappear.
• Most server power supplies accept roughly 200–240 V, which is why 415/240 V works without modification.
• Without PDU transformers, fault current at the rack rises: re-check breaker interrupting ratings and SCCR.

On this page · 6 sections

1. What changes
2. What it saves
3. What it costs
4. Which to choose
5. Common mistakes
6. Frequently asked questions

In the traditional North American design, power is distributed at 480Y/277 V from the UPS, and a PDU transformer near the racks steps it down to 208Y/120 V. Servers are fed 208 V line-to-line. In a 415 V design, a transformer upstream produces 415Y/240 V, which is distributed all the way to the rack. Servers are fed 240 V line-to-neutral, and the PDU transformers disappear.

415/240 V isn't a common utility service voltage in North America, but it's close to the 400/230 V standard used across much of the world. That's why the servers and power supplies built for global markets accept it without modification: most server power supplies are rated for a range of roughly 200 to 240 V.

What changes

	480 V with PDUs	415 V to the rack
Distribution	480Y/277 V	415Y/240 V
At the server	208 V (line-to-line)	240 V (line-to-neutral)
Transformers after UPS	One per PDU	None
Neutral to the rack	Not needed for 208 V loads	Required
Rack connector	NEMA locking types	Often IEC 60309

What it saves

A conversion stage

Every transformer loses some of the energy passing through it, as core loss (always present when it's energized) and load loss (rising with the square of current). A low-voltage dry-type PDU transformer typically loses on the order of 1 to 2% at normal loading, and proportionally more at light load, where data center PDUs often sit. Removing the stage removes those losses, and the heat the cooling system then has to reject. Both show up in PUE.

Current, per kW delivered

Higher voltage means less current for the same power. For a 10 kW rack at 0.95 power factor on a three-phase feed:

Voltage	Current for 10 kW
208 V three-phase	29.2 A
415 V three-phase	14.6 A
480 V three-phase	12.7 A

The same circuit therefore delivers about twice the power at 415 V as at 208 V. With continuous load limited to 80% of the circuit rating (the 80% rule):

Three-phase circuit	Usable at 80%
208 V, 30 A	8.6 kVA
208 V, 60 A	17.3 kVA
415 V, 30 A	17.3 kVA
415 V, 60 A	34.5 kVA

As rack densities climb, that's the practical attraction: fewer circuits, smaller cables and fewer rack PDUs per kW. The formula is kVA = √3 × V × I ÷ 1,000, and every figure above can be checked with it.

Floor space and equipment

Without PDU transformers, the white space loses a row of transformer-based PDUs, often replaced by remote power panels or busway. That's floor space returned to racks, and fewer pieces of equipment to maintain.

What it costs

Higher fault current at the rack

A PDU transformer's impedance limits the fault current available downstream of it. Remove it, and the rack circuits see fault current limited only by the upstream transformer and cables. Branch breakers, busway plug-in units and rack PDUs have to be rated for it (interrupting rating and SCCR), and arc-flash incident energy at the white-space equipment rises. The transformer impedance guide covers the mechanism, and the fault current calculator gives a first estimate.

The neutral comes back

Servers on 240 V are connected line-to-neutral, so the distribution needs a neutral to every rack. Single-phase power supplies on a four-wire system put triplen harmonics into the neutral. Modern power supplies with power-factor correction draw much cleaner current than older designs, but the neutral still needs checking, as the harmonics guide explains.

A dedicated transformer, and equipment choices

Because 415 V isn't the utility service voltage, it comes from a dedicated transformer: either medium voltage to 415 V ahead of a 415 V UPS, or a 480-to-415 V transformer after a 480 V UPS. Every piece of downstream equipment, from switchboards to breakers and rack PDUs, must be rated for 415Y/240 V. Receptacles and plugs are often IEC 60309 types rather than the NEMA configurations North American facilities teams are used to. Equipment that genuinely needs 120 V needs its own source.

Which to choose

• 415 V suits new builds with high rack densities, IT equipment that accepts 240 V throughout, and teams comfortable with IEC-style rack power.
• 480 V with PDUs suits facilities with a mix of 120 V and 208 V equipment, existing 208 V infrastructure, or tenants who expect standard North American receptacles.
• Some designs go further, feeding 480Y/277 V to power shelves in the rack. That removes the step-down entirely, but it needs IT equipment built for 277 V input.

Common mistakes

• Keeping the old breaker ratings. Without PDU transformers, available fault current at the rack rises. Re-check interrupting ratings and SCCR.
• Assuming every device accepts 240 V. Check the input range of everything in the rack, not just the servers.
• Sizing the neutral for balanced linear load. Check it against the actual power supplies.
• Comparing efficiency at full load only. PDU transformers usually run lightly loaded, where their losses are proportionally largest.

Frequently asked questions

Why do data centers use 415 V?

Distributing at 415Y/240 V lets servers be fed 240 V line-to-neutral directly, which removes the PDU transformer stage used in 480 V designs. That saves its losses and floor space, and delivers roughly twice the power per circuit of 208 V.

What voltage do servers get in a 415 V system?

240 V, connected line-to-neutral, since 415 divided by the square root of three is 240. Most server power supplies accept a range of roughly 200 to 240 V, so the same units work on 208 V and 240 V.

Does 415 V distribution increase fault current?

At the racks, usually yes. The PDU transformers it eliminates also limited fault current downstream of them. Branch breakers, busway plug-ins and rack PDUs need interrupting ratings and SCCRs for the higher value, and arc-flash labels need recalculating.

How much power does a 415 V 30 A circuit deliver?

A three-phase 415 V, 30 A circuit loaded to 80% delivers about 17.3 kVA (√3 × 415 × 24 A). The same breaker at 208 V delivers about 8.6 kVA.

Next steps

The Data Center Power Distribution reference covers the busway, PDUs and remote power panels involved, and the Rack Elevation Builder budgets rack power against circuit capacity.

Run the numbers

• Plan a rack before you order the rail kit.Stack equipment into a rack and check U-space, circuit power and weight budgets.
• Available Fault Current CalculatorAvailable symmetrical fault current at a transformer secondary.
• Voltage Drop CalculatorFeeder drop against the 3% and 5% design limits.
• Transformer Sizing CalculatorkW load to the next standard kVA nameplate.

Read next

• Transformer Impedance (%Z) ExplainedWhy removing a transformer stage raises fault current downstream
• PUE ExplainedWhere conversion losses show up in facility efficiency
• N+1 vs. 2N Redundancy ExplainedCarrying A and B feeds to the rack at either voltage

Equipment

• Data Center Power DistributionBusway, PDUs and remote power panels.
• Data Center TransformersIncluding the transformers that produce 415 V.