The Harmonics We Had to Live With [/ðə hɑrˈmɑnɪks wi ˈhæd tɪ ˈlɪv wɪθ/] n - The constraint. The nonlinear switching power supplies in every server draw current in sharp pulses rather than smooth sine waves, injecting harmonic currents back onto the The Current That Comes in Threes system. At scale this distorts voltage, overheats neutrals and transformers, and strains upstream equipment. It is inherent to how the IT load works; one cannot ask thousands of servers to cease being nonlinear.

Why no clean fix exists at this level. [/waɪ nəʊ ˈfɪks/] n - The textbook cures are big and upstream: oversized transformers, active harmonic filters, or a wholesale move toward 800-volt DC distribution that sidesteps the AC harmonic problem entirely. Those are redesigns and capital projects, not things a floor engineer specs on a Tuesday. The harmonic source is the load itself, and the load is the whole point of the building.

The workarounds we actually used. [/ðə ˈwɜːkəˌraʊndz/] n

• K-rated transformers and upsized neutrals [/ˈkrætɛd ˈtrænsfɒrmɛrs ˈænd ˈʌpsɪzɛd ˈnɛʌtræls/] n where we already had them, derating equipment to endure the heat rather than abolish its cause.
• Balancing the phases. [/ˈbælænkɪng ˈthɛ ˈphæsɛs/] n We spread nonlinear loads as evenly as we could across phases, lest third-harmonic currents all pile onto a shared neutral: a careful Power distribution unit and Rack power distribution unit loading discipline.
• Monitoring instead of curing. [/ˈmɒnɪtɒrɪng ˈɪnstɪːd ˈɒf ˈkʌrɪng/] n We trended total harmonic distortion continuously, so we would see it approach the bounds of what the gear could abide and could shift load before anything overheated.
• Respecting it at design margin. [/ˈrɛspɛktɪng ˈɪt ˈæt ˈdɛsɪgn ˈmærgɪn/] n New rows were laid out assuming the distortion would be present, rather than feigning clean power and discovering the truth at a hot neutral.

What it cost. [/wɒt ɪt ˈkɒst/] n - We carried derated equipment and a permanent monitoring burden. The distortion never departed; we merely kept it within the envelope the hardware could survive, and let the true cure ride along with the move to DC distribution in The New Buildout.

Part of Problems We Could Only Work Around.