AS400 Power Requirements

In infrastructure planning, power requirements can mean voltage, amperage, circuit availability, cooling load, rack space, and power distribution for the physical machine. In upgrade planning, power requirements can mean how much CPU, memory, storage, and IBM i licensing tier a workload needs on the replacement server.

Before anyone gives an answer, make sure the discussion is about facility power, compute power, or both.

Facility power questions rarely happen in isolation. A buyer usually asks them after a model, quote, used hardware option, relocation date, or replacement part is already being discussed. That puts the query near the buying decision, even when the wording sounds technical.

The practical answer should help the buyer confirm whether the room can support the system: circuit type, plug and receptacle, PDU capacity, UPS runtime, rack depth, rail fit, cooling load, front and rear service clearance, and who signs off before delivery.

Once the buyer has rack, UPS, PDU, circuit, and cooling requirements, the next question is how far to take the install. A basic install gets the known machine running safely. A sustainable install adds monitoring, tested UPS runtime, cleaner power separation, and better documentation. A growth install reserves room for a future Power server, storage drawer, HA equipment, network refresh, or longer runtime target.

That is not too far down the funnel for this query. It is the natural follow-up, because facility requirements only matter when someone has to make the room ready for a real system.

There is no single AS400 electrical requirement because the platform spans decades of hardware formats. Older deskside and cabinet systems, later iSeries and System i machines, and current IBM Power rack servers all differ in plug type, voltage expectations, cooling needs, and physical footprint.

That means relocation, colo planning, or decommissioning work should always start with the exact model and feature configuration. The right source is the machine's hardware documentation or a vendor who can match the serial and model details to the correct facility requirements.

If the machine type on the serial tag begins with 9406, the AS/400 and iSeries era figures are collected in AS/400 9406 Power Requirements by Model, covering the 270, 800, 810, 820, 825, 830, 840, 870 and 890 with IBM rated voltage, phase, kVA, watts and thermal output.

The entry machine is where most AS400 power questions land, because it is the class that replaces an older box in a room that was never built as a data center. IBM publishes a rated maximum and a maximum thermal output for every machine type. These are the entry-class figures across the generations still found in production.

The trend matters more than any single row. Entry-class rated draw climbed to 1,600 W at Power 9, then fell to 1,075 W at Power 10 and 550 W at Power 11. A shop replacing an S914 with an S1112 is cutting rated load by roughly two thirds while keeping the same 120 V circuit. Full machine-type tables, including the 2U and 4U scale-out models and the enterprise nodes, are on the generation references: Power 5, Power 6, Power 7, Power 8, Power 9, Power 10, Power 11, and Power 12.

This is the distinction that changes a facility plan. The rated maximum on a specification sheet is a nameplate figure for circuit and breaker sizing. It is not the load the machine puts on the room. IBM also publishes measured idle and measured maximum draw, and the gap between the two numbers is large.

A two-socket S924 rated at 2,750 W measures between 886.9 W and 964.9 W at maximum. An S914 rated at 1,600 W measures under 351 W. Sizing a UPS, a PDU, or a cooling budget against the nameplate can overspend by a factor of three. Size the circuit and breaker against the rated maximum, because that is what the nameplate is for, and size runtime and cooling against measured draw.

UPS capacity is quoted in VA and server load is quoted in watts. Convert with the power factor: VA equals watts divided by power factor. Modern IBM Power supplies run near 0.98, so the two numbers are close. Then leave headroom by loading the UPS to no more than about 80 percent of its rating, which protects runtime and allows for a failed module in a redundant pair.

Worked from the table above: a two-socket S924 at a measured maximum of 964.9 W needs roughly 985 VA. At 80 percent loading that calls for a UPS of about 1.25 kVA for the server itself. Sized against the 2,750 W nameplate instead, the same machine appears to need roughly 3.5 kVA. Both are defensible numbers, but they buy very different equipment.

Runtime is the second decision and it is not linear. Halving the load more than doubles the runtime, so a UPS sized close to its limit gives up runtime quickly. Decide the target first: enough to ride out a brief interruption, enough to complete a controlled power down, or enough to carry the workload until a generator takes over. That choice, not the server nameplate, usually sets the budget.

Most IBM Power servers ship with redundant dual line cords. Two cords on one circuit gives supply redundancy but not circuit redundancy. Feeding them from separate circuits, and ideally separate UPS units, is what makes the redundancy real.

For most modernization projects, the more important issue is not wall power ... it is workload sizing. Teams need to understand current utilization, CPW, memory footprint, storage growth, and IBM i software tier before choosing a replacement server.

This is where an old AS400 discussion becomes an IBM Power sizing discussion. Start with IBM Power Sizing Basics if the goal is selecting the right current-generation hardware rather than moving an old system physically.

Useful inputs include the current model number, serial number, processor configuration, current IBM i release, storage usage, workload growth expectations, facility circuit details, rack space, and cooling constraints. Without those details, any answer about AS400 power requirements will be too generic to trust.

If the real decision is whether to keep the legacy machine or replace it with a newer platform, What Replaced AS400? is the next page to read. If the concern is support risk rather than facility sizing, see AS400 Support and AS400 End of Life.

For the hardware-specific checklist, use AS400System.com's AS400 Power Requirements by Model. For the commercial upgrade version, use AS400IBMSystem.com's Power Requirements Planning Guide. If the next step is finding a partner for UPS, PDU, rack, cooling, power supply, or installation help, use BigTechReseller.com's AS400 Power Requirements partner page.