Why is the derated current higher than the load current?

Because a breaker must not carry more than 80 % of its rating continuously (NEC 210.20(A)). A 12 A continuous load therefore needs a 12 ÷ 0.8 = 15 A device, which rounds up to the next standard size of 16 A — not 12 × 0.8 = 9.6 A.

Which voltage do I enter for a three-phase feed?

The line-to-line voltage — 400 V for a European 230/400 V supply, 208 V for a North American 120/208 V supply. The formula divides by √3 × V, so entering the phase-to-neutral voltage would overstate the current by a factor of √3.

What power factor should I use?

0.95 if you do not know, which is where modern 80 PLUS Gold and Titanium supplies are typically rated. A lower power factor draws more current for the same real power, so 0.9 is the more conservative assumption; a measured figure always beats both.

How many C13 and C19 outlets does my rack need?

The tool reports the minimum receptacles that can carry the load at the derated per-outlet rating, assuming 25 % of the load lands on C19 (16 A) receptacles and the rest on C13 (10 A). Feed it your real bill of materials for an exact count.

Is the calculation sent anywhere?

No. Every figure is computed in your browser and the page makes no network requests.

PDU Power & Breaker Calculator

From vendor documentation

Turn a rack load in watts into line current for single- or three-phase feeds, apply the 80 % continuous derating, pick the next standard breaker size and count the C13 and C19 receptacles the load needs.

Input

Load

Total load (W)

Real power drawn by everything in the rack. Every watt becomes heat.

Voltage (V)

Three phase takes the line-to-line voltage: 400 V for 230/400 V, 208 V for 120/208 V. Single phase takes the line-to-neutral voltage: 230 V or 120 V.

Phases

Power factor

Real power ÷ apparent power. Defaults to 0.95; lower draws more current, so 0.9 is the conservative choice.

Plan for A/B (2N) feedsSize both feeds for the whole rack, not half of it.

Export

The calculation and the device breakdown

Line current

7,150 W at 400 V three phase (line-to-line)

Line current: 10.86 A
Apparent power: 7.53 kVA
Derated working current: 13.58 A

Substituted formula

I = P / (√3 × V_LL × PF) = 7150 W / (1.7321 × 400 V × 0.95) = 10.86 A

Recommended breaker

Breaker rating: 16 A
Continuous headroom: 12.80 A

How this was chosen

10.86 A continuous ÷ 0.8 = 13.58 A, rounded up to the next standard rating of 16 A. The 80 % continuous-load rule (NEC 210.20(A)) leaves 12.8 A of continuous headroom on a 16 A device.

6 A10 A13 A16 A20 A25 A32 A40 A50 A63 A80 A100 A125 A

PDU and receptacles

IEC C13 outlets: 2
IEC C19 outlets: 1
C13 working limit: 8 A
C19 working limit: 12.8 A

Receptacle count is a minimum, not a BOM

At 16 A and above, plan A/B feeds from separate panels and size each feed for the full rack load. A single feed is an N configuration — one breaker trip takes everything down.

Conventions and assumptions

What is a rule, and what is a choice

80 % continuous derating (rule). A device carrying a load for three hours or more must not exceed 80 % of its rating, so the derated current is amps ÷ 0.8 and the breaker rounds up from there (NEC 210.19(A)(1), 210.20(A)).
Standard breaker list (convention). The sizes offered are the IEC 60898-1 / IEC 60364-4-43 preferred values up to 63 A plus the common North American 80 A, 100 A and 125 A. NEC 240.6(A) also lists 15 A, 35 A, 45 A and 60 A, which are rare on rack PDUs.
Power factor (convention). The default is 0.95, where modern 80 PLUS Gold and Titanium supplies are typically rated. A lower power factor draws more current, so 0.9 is the conservative choice when the nameplate data is unknown.
IEC 60320 ratings (rule). C13 is rated 10 A and C19 16 A; the working figures shown are those ratings after the 80 % derating.
C13/C19 split (convention). Outlet counts assume 25 % of the load lands on C19 receptacles and the rest on C13. The number reported is the minimum that carries the load, not a recommended BOM.

Frequently asked

Why is the derated current higher than the load current?: Because a breaker must not carry more than 80 % of its rating continuously (NEC 210.20(A)). A 12 A continuous load therefore needs a 12 ÷ 0.8 = 15 A device, which rounds up to the next standard size of 16 A — not 12 × 0.8 = 9.6 A.
Which voltage do I enter for a three-phase feed?: The line-to-line voltage — 400 V for a European 230/400 V supply, 208 V for a North American 120/208 V supply. The formula divides by √3 × V, so entering the phase-to-neutral voltage would overstate the current by a factor of √3.
What power factor should I use?: 0.95 if you do not know, which is where modern 80 PLUS Gold and Titanium supplies are typically rated. A lower power factor draws more current for the same real power, so 0.9 is the more conservative assumption; a measured figure always beats both.
How many C13 and C19 outlets does my rack need?: The tool reports the minimum receptacles that can carry the load at the derated per-outlet rating, assuming 25 % of the load lands on C19 (16 A) receptacles and the rest on C13 (10 A). Feed it your real bill of materials for an exact count.
Is the calculation sent anywhere?: No. Every figure is computed in your browser and the page makes no network requests.

Frequently asked

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