At Power Factor 0.85, a 200 kW Chiller Circuit Passes a 320 A Screen at 432 V and Fails at 415 V

A small-module study derived from our GB300-class reference design carries a chiller with a 200 kW three-phase electrical input on a circuit screened at 320 A [STUDY]. At the study's working voltage of 432 V and a power factor of 0.85, the current is 314.5 A. That is 5.5 A below 320 A, a margin of 1.7 percent [STUDY]. At 415 V and the same power factor, the current is 327.3 A, 7.3 A above 320 A, and the screen fails [STUDY]. The screen is worth keeping. A pass this thin has to carry its conditions in writing, and 320 A is not the ampacity the conductors are finally sized to.

The arithmetic

Three-phase current is power divided by the square root of 3, the line voltage and the power factor: I = P / (√3 × V × PF).

The same 200 kW at other voltages and power factors:

All values are [STUDY]. One cell is above 320 A: 415 V at a power factor of 0.85.

One product sets the result

At 200 kW, the 320 A screen passes when voltage times power factor is at least 360.85 [STUDY]. Each limit below is rounded so that the current stays at or under 320 A:

• At a power factor of 0.85, the voltage has to stay at 424.6 V or above. The formula minimum is 424.52 V, 7.5 V below 432 V.
• At 432 V, the power factor has to stay at 0.836 or above.
• At 415 V, the power factor has to reach 0.870, or the load has to come down to 195.51 kW at a power factor of 0.85.

Neither input is fixed yet. The voltage that matters is the one at the chiller terminals. It depends on which source is feeding the bus, utility or generator, and on the drop along the cable. The power factor belongs to a chiller that has not been selected [HOLD]. Written in full, the screen reads: passes at 200 kW if terminal voltage times power factor is at least 360.85. When the nameplate arrives, that first check is quick. The checks listed under "What closes it" still follow.

The computed current is not what the conductors are sized to

A chiller is motor-compressor equipment. In a US build, the conductors from the last short-circuit and ground-fault protective device to the chiller are a branch circuit under NEC Article 440. Their ampacity may not be less than the nameplate minimum circuit ampacity, or MCA (NEC 440.35) [FACT]. The MCA method in NEC 440.33 takes 125 percent of the largest motor-compressor's rated-load current or branch-circuit selection current, whichever is greater, and adds the other motor loads at 100 percent. Other loads are added under NEC 440.34 [FACT]. The branch-circuit short-circuit and ground-fault protective device may not exceed the nameplate maximum overcurrent protection, or MOCP (NEC 440.22(C)) [FACT].

The MCA is not the current computed above. A circuit that passes on the computed current can still fail on the MCA.

This 125 percent is a motor-compressor rule. The 125 percent factor for continuous loads is a different rule with the same number, in NEC 210.19(A)(1), 215.2(A)(1) and 230.42(A)(1) [FACT]. The service cap and the 125 percent rule covers that factor on the medium-voltage side.

320 A is a screen, not a device

320 A is not one of the standard fixed ratings in NEC 240.6(A), which step from 300 A to 350 A [FACT]. In the study it is a trial screening value, not a selected breaker and not a selected cable. In a US build it has to become two real things. One is a conductor ampacity after correction for ambient temperature and adjustment for more than three current-carrying conductors together, under NEC 310.15(B) and (C) in the 2020 and 2023 editions [FACT]. The other is a protective device on a real rating step. Where an adjustable-trip breaker is used, NEC 240.6(B) and (C) decide which setting counts as its rating [FACT]. Either result can land above or below 320 A. The screen does not predict which.

What closes it

The circuit is checked again with the selected chiller's data, in this order:

1. Nameplate voltage, MCA and MOCP.
2. The starting method and starting current curve, and the voltage dip they cause on each source.
3. The terminal voltage on each source, with the real cable length and impedance.
4. Conductor ampacity after correction and adjustment for the actual route.
5. Short-circuit current and protection curves for each source mode, so that the chiller's device coordinates with the devices above and below it.

The study applies the same check to each of the eleven circuits on that side of the module. A group budget sums only the equipment connected to that group [STUDY]. The five checks above are still open on each of these circuits [HOLD].

Limits and open items

Confirmed: the three-phase current formula. [FACT]

Code references: NEC 440.22(C), 440.33, 440.34 and 440.35 for motor-compressor branch circuits; NEC 240.6(A) to (C) for ratings; NEC 310.15(B) and (C) for ampacity correction and adjustment. The edition that applies is set by the jurisdiction. [FACT]

Study values: 200 kW, 320 A, 432 V and 415 V as study inputs; every current in the table; the 360.85 product, the 424.6 V, 0.836 and 0.870 limits, and the 195.51 kW limit. [STUDY]

Open: the chiller is not selected, so its nameplate voltage, power factor, MCA, MOCP and starting current are unknown. Cable routes and lengths are model center lines, not measured runs. No short-circuit or coordination study has been done for this circuit. [HOLD]

Closing observation

A screen that passes by 5.5 A, 1.7 percent of 320 A, is a pass with a condition attached: terminal voltage times power factor at least 360.85. Writing that condition next to the result costs one line. Leaving it out turns a later nameplate at 415 V, or a power factor below 0.836 at 432 V, into a surprise at submittal review.

© 2026 K&K Data Service Inc. All rights reserved. Reproduction or republication is permitted only with clear attribution to K&K Data Service Inc. and a working hyperlink to the canonical URL of this article. Excerpts must preserve the technical context, maturity labels, assumptions, and limitations. No excerpt may imply project approval, field validation, certification, or endorsement that the original article does not state.

Source: K&K Data Service Inc., "At Power Factor 0.85, a 200 kW Chiller Circuit Passes a 320 A Screen at 432 V and Fails at 415 V," https://www.kkdatasvc.com/lab/electrical-architecture-and-failure-domains/a-200-kw-chiller-circuit-passes-a-320-a-screen-at-432-v-and-fails-at-415-v/.