Simplex Nautilus-250 Load Bank

250 kW water-cooled resistive load bank for indoor data-center use

Simplex Nautilus-250 Load Bank is one of 16 load banks tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.

Simplex Nautilus-250: 250 kW resistive water-cooled load bank, 480 V 3-phase, Type 1 indoor, 125 GPM, 900 lb dry, 8-inch TFT HMI. Current production.

The Simplex Nautilus-250 is a 250 kW resistive, water-cooled, Type 1 indoor load bank manufactured by Simplex, Inc. (5300 Rising Moon Rd., Springfield, IL 62711), an operating company of TerraVest Industries Inc. The unit is a current, actively produced product — it is featured on the simplexdirect.com homepage, carries a full live specification page with no discontinuation or last-time-buy language, and is stocked in Simplex's own rental fleet as the Nautilus-250R. A Simplex factory-certified used-equipment channel separately lists the Nautilus 250, placing it in the unusual position of having a manufacturer-run refurbished path competing alongside dealer stock on the secondary market. The load bank is rated resistive at 1.0 power factor, so every capacity figure is in kilowatts, not kilovolt-amperes. The unit accepts 480 VAC, 3-phase, 3-wire power at 60 Hz and delivers 0–250 kW continuously. The factory-certified used-equipment list also documents a derated output of 187.5 kW at 416 V, 3-phase, confirming that 416 V installations exist; however, Simplex publishes no full voltage-option table or 50 Hz variant for the Nautilus-250. Confirm the exact voltage and frequency configuration on the nameplate before purchase. Heat rejection is the defining design choice. A 250 kW resistive load bank operating indoors must reject 250 kW of thermal energy; an air-cooled unit of that capacity either dumps it into the occupied space or requires a duct penetration and a louver. The Nautilus routes all heat into a water loop instead. At nominal conditions, Simplex publishes a flow rate of 125 GPM yielding approximately 12.5°F rise at full load. Simplex's own sizing formula — kW = GPM × ΔT°F × 0.16 — reconciles exactly: 125 × 12.5 × 0.16 = 250 kW. That same formula is the buyer's field tool for verifying performance against a known supply flow rate. Outlet water temperature must not exceed 180°F; no inlet temperature or inlet pressure limit is published. The unit is freestanding and portable at approximately 900 lb dry (approximately 1,600 lb full of water), housed in a Type 1 indoor aluminum-frame enclosure measuring 72 inches high × 24 inches wide × 36 inches deep (H × W × D). At 24 inches wide it moves through a standard door, which is the physical reason a single data-center facility can deploy a fleet of them — and why a single decommissioning event can release dozens onto the secondary market at once. Power connection is via cam-type lugs, one 4/0 (400 A) per phase plus one ground. Control power is 120 V, 15 A, supplied externally via a power cord. Load control combines branch-circuit contactors with triac trimming. The contactor circuit topology is 25-25-50-50-50-50 kW, for six discrete switched stages. Triac control then interpolates continuously between those stages, and Simplex markets the result as infinitely variable output from 0 to 250 kW. Both descriptions are accurate: the coarsest single switched increment is 25 kW (10% of full scale), and triac trimming eliminates discrete steps between those coarse points. The on-board PLC drives an 8-inch color TFT touchscreen HMI and supports local or remote operation. Protection circuits monitor high outlet temperature, low flow, and high pressure via a flow transducer, inlet and outlet thermocouples, and a pressure sensor. Immersion-type tubular resistive elements are sheathed in stainless steel or Incoloy with a chromium-alloy conductor. Switching is handled by triacs and branch-circuit contactors. A motorized proportioning valve controls water flow through the heat-exchange section. These elements are in contact with the water loop and accumulate scale and pitting over time — a wear mode that air-cooled units do not experience and that used-unit buyers must inspect specifically. The Nautilus is one of only two water-cooled load bank products currently in the Simplex catalog (alongside the LBW), and it is the only water-cooled portable unit in the Simplex rental fleet apart from the larger Atlantis 500R.

Why it matters

The Nautilus-250 solves a siting problem that affects nearly every large indoor data center: 250 kW of resistive load is a meaningful test increment, but 250 kW of hot exhaust air in a sealed data hall disrupts thermal management and can violate fire-suppression and HVAC design assumptions. By routing heat into the facility's existing water loop, the Nautilus makes full-load generator and UPS testing practical in spaces where air-cooled equipment of comparable capacity would be operationally prohibited. Its compact footprint — 24 inches wide, rolling through a standard door — multiplies that advantage for fleet deployments where many units must reach equipment under test.

Who buys it

The primary buyer is a data center or critical-facility operator whose generator, UPS, or power infrastructure commissioning and periodic exercise requirements cannot be met by an air-cooled load bank. The constraint is indoor heat rejection: where no roof location, yard pad, or louver path is available for 250 kW of exhaust air, the Nautilus connects to an existing chilled-water or condenser-water loop and removes the heat in the water circuit instead. Facilities running integrated system testing (IST) or Level 5 acceptance testing in enclosed mechanical rooms, or testing UPS and generator sets in fully enclosed data halls, are the natural operators. Secondary buyers include rental fleet operators — Simplex itself runs a rental-fleet version (Nautilus-250R) and several national rental companies carry water-cooled load banks — and buyers of decommissioned data-center equipment. A large data center that retires a fleet of Nautilus units releases them in quantity, which is the origin of multi-unit used lots. The manufacturer's own factory-certified used-equipment channel is an active procurement path for this model specifically.

Role in the data center

The Nautilus-250 is used as the primary load source for generator and UPS acceptance testing, integrated system testing (IST), and periodic loaded-run exercises inside data centers where air-cooled load banks cannot be used due to indoor heat-rejection constraints. Its compact width allows deployment inside data halls, mechanical rooms, and corridors that would be inaccessible to larger equipment. In fleet configurations — multiple units daisy-chained or independently cabled to the power bus under test — it can aggregate to megawatt-class test loads while keeping all heat in the facility water loop. Simplex markets the Nautilus-250R as a rental unit for the same commissioning and periodic testing purposes, which means the equipment is familiar to commissioning contractors who have rented it and may later recommend purchase. According to Simplex's own load bank fundamentals page, Simplex load banks can be used to satisfy the requirements of the National Fire Protection Association (NFPA) for emergency standby power systems; this is a vendor claim and the specific NFPA 110 section numbers, test percentages, and durations were not cited on that page.

Key specifications

Technical summary

Load type: Resistive (1.0 power factor) Capacity: 250 kW, 0–250 kW continuously variable Voltage: 480 VAC, 3-phase, 3-wire Derated rating: 187.5 kW at 416 V, 3-phase Frequency: 60 Hz Load step resolution: 25-25-50-50-50-50 kW contactor circuits; triac-trimmed for infinitely variable 0–250 kW Cooling: Water-cooled, motorized proportioning valve Nominal water flow: 125 GPM (~12.5°F rise at full load) Sizing formula: kW = GPM × ΔT°F × 0.16 Maximum outlet water temperature: 180°F Water connections: 2-inch inlet and outlet, quick disconnects Elements: Immersion type, tubular, stainless steel or Incoloy sheathed, chromium-alloy conductor Power connection: Cam-type, 1 × 4/0 (400 A) per phase plus 1 ground Enclosure: Type 1, freestanding, indoor, portable; aluminum frame clad in aluminum Dimensions: 72"H × 24"W × 36"D Weight: ~900 lb dry, ~1,600 lb full of water Ambient rating: 52°C Control: PLC with 8-inch color TFT touchscreen HMI, local or remote Control power: External 120 V, 15 A via power cord Protection: High outlet temperature, low flow, high pressure; flow transducer, inlet/outlet thermocouples, pressure sensor Duty: Continuous

Major variations

The Nautilus-250 is the sale (permanent-purchase) configuration. The Nautilus-250R is Simplex's own rental-fleet variant, documented in a separate datasheet (doc code 1409-05.02, © 2021 Simplex, Inc.); published specifications on the 250R datasheet match the sale unit. No additional capacity variants (e.g., a Nautilus-500) appear in the Simplex water-cooled catalog; the only other portable water-cooled unit in the Simplex rental fleet is the larger Atlantis 500R, which is a separate product. Simplex's factory-certified used-equipment list documents a 187.5 kW derated output at 416 V, 3-phase, confirming that 416 V installations exist, but no full voltage-option table is published. Confirm the voltage configuration on the nameplate before purchase.

Configurations and options

The Nautilus-250 ships as a self-contained freestanding unit with a PLC-based 8-inch color TFT touchscreen HMI as standard. Load control is a combination of branch-circuit contactors and triac trimming. Water connections are 2-inch quick-disconnect fittings at inlet and outlet. Power connection is cam-type lugs. Control power is drawn from a standard 120 V, 15 A outlet via a supplied cord. No optional voltage or frequency variants are documented in the published brochure beyond the standard 480 V, 60 Hz configuration. Confirm with Simplex at 1-800-637-8603 whether 416 V or other voltage builds are available to order.

Compatibility and dependencies

The Nautilus-250 requires a water supply capable of delivering at least 125 GPM to achieve full 250 kW output with the published 12.5°F temperature rise. At lower flow rates, the same load produces a higher outlet temperature rise; Simplex's formula kW = GPM × ΔT°F × 0.16 governs: at 100 GPM full load requires 15.6°F rise, at 80 GPM it requires 19.5°F rise. Water connections are 2-inch quick-disconnect fittings. The power connection requires cam-type lugs accepting 4/0 (400 A) conductors per phase plus a ground conductor on a 480 VAC, 3-phase, 3-wire circuit at 60 Hz. Control power requires a separately fused 120 V, 15 A outlet. The unit is Type 1 rated and must be installed indoors; it is not rated for outdoor or wet locations.

Pricing and availability

Lead time, new: Build-to-order; not listed on Simplex's published Quick Ship program (which tops out at 700 kW air-cooled units). Simplex's terms state quotations are firm for 60 days, delivery dates are best estimates only, and non-standard equipment requires 10% down at order plus 10% at engineering release and 25% at production release. No specific lead time in weeks is published.. Lead time, used or refurbished: Simplex publishes no delivery time for factory-certified used units. The Simplex factory-certified used channel lists Nautilus 250 inventory; availability and timing require a call to 1-800-637-8603.. Warranty, new: 12 months from date of shipment (standard). Extended Two Year Field Service warranty (24 months from shipment, field repair by Simplex technicians, materials and labor included) available for 48 contiguous U.S. states only; does not cover start-up services.. Warranty, used: Confirm coverage terms directly with Simplex or the selling dealer..

Lifecycle and maintenance

Simplex publishes no MTBF, design life in hours, or element life figure for the Nautilus-250. The standard warranty is 12 months from date of shipment from the factory, covering repair or replacement of parts defective in material or workmanship under normal service. An Extended Two Year Field Service warranty covering 24 months from shipment — including field repair or replacement by Simplex technicians with materials and labor — is available for installations in the 48 contiguous U.S. states only and does not cover start-up services. Both warranties exclude equipment improperly specified by the buyer, improperly stored or handled, improperly mounted or connected, operated outside nameplate specifications, not properly maintained, or containing non-standard parts. Simplex's published maintenance schedule applies to the Nautilus as follows. At each operation: check for obstructions at intake and exhaust paths; inspect load branches for blown fuses or opened load resistors; verify three-phase currents are essentially equal. Every 50 hours or 6 months, whichever comes first: check tightness of all electrical connections; units transported over the road require shorter connection-check intervals. Motor lubrication uses polyurea mineral oil NGLI grade 2 grease (published compatible products: Chevron SRI #2, Rykon Premium #2, Exxon Polyrex EM, Texaco Polystar RB); intervals range from 3 years to 3 months for standard use (up to 16 hr/day, max 100°F) and from 1 year to 1 month for severe use (over 16 hr/day, 100–150°F), with charge volumes of 0.25 to 3.00 cubic inches by NEMA frame 140–500. The Nautilus adds a wet-side subsystem that air-cooled load banks do not have: a motorized proportioning valve, flow transducer, inlet and outlet thermocouples, a pressure sensor, and immersion elements in contact with the water supply. This wet loop requires periodic inspection for scale and pitting on element sheaths and internal tubing — corrosion and mineral buildup are the dominant aging mechanisms on the water side and have no equivalent in air-cooled units. A unit that was not properly drained before storage or transport will weigh approximately 1,600 lb rather than 900 lb dry; verify drain status before moving.

Thermal and emissions profile

No on-site combustion, no direct emissions and no hot-air discharge. The full 250 kW is rejected into the water loop, which is why the unit can be run indoors in a live data hall: the heat is handed to the cooling plant rather than to the room. Confirm the loop has 250 kW of spare rejection capacity before loading it.

Common failure points

• Immersion resistive elements — Reduced kW output or phase imbalance; more than 5% below rated output
• Immersion element sheaths — Progressive output degradation; visible scale, pitting, or corrosion on stainless steel or Incoloy sheaths
• Motorized proportioning valve — Inadequate flow control; outlet temperature exceeds 180°F limit; low-flow alarm
• Flow transducer — Low-flow alarm with normal supply pressure; inaccurate GPM reading
• Inlet/outlet thermocouples — Open-thermocouple alarm; false over-temperature indication
• Triac control circuit — Loss of continuously variable output; unit steps only in 25 kW or 50 kW increments
• PLC / HMI — Black or dark screen; communication errors; RTE-500 SRAM checksum error; RTE-002 log failure
• Metering fuses MF 1-3 and voltage transducer connections — Displayed voltage zero, imbalanced, or incorrect; current zero or off; kW reading low, negative, or off
• Electrical connections — Intermittent faults; elevated resistance at terminals; potential arc damage

Inspection checklist

• Verify nameplate voltage, frequency, and phase configuration match the intended supply (480 VAC, 3-phase, 3-wire, 60 Hz standard; confirm 187.5 kW / 416 V derate if applicable)
• Weigh the unit or confirm drain status: ~900 lb dry vs ~1,600 lb full of water; an undrained unit was not properly decommissioned
• Measure phase-to-phase resistance A-B, B-C, C-A across all element circuits; Simplex states all three readings must be balanced; unbalanced readings indicate open elements
• Load the unit to nameplate and verify output within 5% of 250 kW; apply Simplex's voltage-correction formula before judging: kW output = kW rated × (V input ÷ V rated)²; at 460 V on a 480 V unit the expected output is 91.8% of nameplate — not a defect
• At nominal 125 GPM supply, verify outlet temperature rise is approximately 12.5°F and outlet temperature does not exceed 180°F; use Simplex's formula kW = GPM × ΔT°F × 0.16 to cross-check
• Inspect both 2-inch quick-disconnect water fittings for seal condition, corrosion, and damage
• Inspect immersion element sheaths (stainless steel or Incoloy) for scale accumulation, pitting, and surface corrosion — the primary aging mode on water-cooled units
• Verify the motorized proportioning valve operates through its full range and responds to controller commands
• Verify the flow transducer produces a reading consistent with the measured supply flow; confirm it is not clogged or corroded
• Check both inlet and outlet thermocouples: confirm connections are tight at PLC terminals and thermocouple wire is unbroken; a loose thermocouple produces a false high-temperature alarm
• Confirm the pressure sensor is connected and reads a plausible value; confirm high-pressure alarm set point with Simplex (no threshold is published)
• Check all electrical connections for tightness; Simplex specifies inspection every 50 hours or 6 months, and over-the-road transport requires shorter intervals — a trailered used unit is the higher-risk case
• Check metering fuses MF 1-3 and voltage transducer connections; blown fuses cause zero, imbalanced, or incorrect voltage and kW readings that can be misread as element failure
• Verify cam-type power lugs on all three phases and the ground conductor are undamaged and fully seated
• Confirm PLC Power LED and Run LED are both green; test HMI touchscreen across all panels; shine a flashlight on a dark or dim screen to distinguish backlight failure from a dead HMI
• Confirm the 120 V, 15 A control power cord and outlet connection are intact and the cord jacket is undamaged
• Confirm the Type 1 enclosure panels are fully closed, sealed, and free of field modifications; Type 1 is an indoor rating and any breach affects the enclosure classification
• Verify the UL/CUL listing label is intact and legible

Procurement channels

Simplex sells the Nautilus-250 direct through its own sales channel; contact Simplex at 1-800-637-8603 or via simplexdirect.com for new-unit quotations. No list pricing is published on the manufacturer's website. Simplex operates a factory-certified used-equipment channel (SimplexUsedEquipment.pdf, available at simplexdirect.com) that lists the Nautilus 250 alongside other refurbished units; pricing requires a call rather than being shown on the document. Simplex also runs a rental fleet with the Nautilus-250R available for short-term and long-term rental; no rental rate is published on the rental page or the 250R datasheet. Buyers should obtain at least one quote from the Simplex factory-certified channel before committing to dealer stock, as the manufacturer competes directly in the used market for this model.

Regional notes

The Simplex factory is in Springfield, IL; all shipments are F.O.B. Springfield, Illinois and the buyer pays freight. The Extended Two Year Field Service warranty is available only for installations in the 48 contiguous U.S. states and does not cover start-up services. The standard 60 Hz, 480 VAC configuration targets North American markets. A 416 V derated output is documented on the factory used-equipment list, and the Nautilus-250R rental datasheet is copyright 2021, both indicating the unit has a North American installed base. No 50 Hz variant is documented in any published Simplex source; confirm availability of international voltage or frequency configurations directly with Simplex before specifying for non-North American installations.