Compared › ±400 VDC vs 800 VDC
±400 VDC vs 800 VDC
Past roughly 200 kW per rack the AC chain hits a current wall — I²R losses, breaker frames, and copper mass stop scaling. The fork is no longer whether to go DC but which DC, and the two camps are betting on different things.
| Axis | ±400 VDC | 800 VDC |
|---|---|---|
| The bet | ride the EV supply chain: 400 V-class parts at automotive volume | collapse the chain: one step from MV to the rail |
| Reference design | Meta / OCP Mt. Diablo bipolar sidecar | NVIDIA Kyber-class (~600 kW racks) + solid-state transformer path |
| Copper / current | halves current vs 415 VAC for the same power | +157% power through the same copper vs 415 VAC |
| Conversion chain | more stages than 800 V, fewer than legacy AC | SST prototype: 13.2 kVAC → 800 VDC at ~98%; ~87% utility-to-VRM end-to-end |
| Parts maturity | breakers, connectors, insulation class all shipping today | protection and arc-fault engineering at 800 VDC is genuinely new |
| Where AC stays | — | both camps agree: below ~200 kW/rack and for everything non-AI, 415 VAC remains the default |
How the decision falls
±400 V buys a supply chain; 800 V buys the shortest chain. If your roadmap tops out near 200–300 kW racks, the EV parts bin is the pragmatic play; if you are underwriting 600 kW Kyber-class racks, the single-step 800 V architecture is what the density actually demands.
Full derivations, worked examples, and the numbers behind this matrix: The DC power revolution (Ch 4.7) · The I²R wall: busway to rack (Ch 4.6) · Transformers and the SST (Ch 4.4)