Resistive load banks for testing generators and power systems · Rating, voltage and load-step resolution, load tolerance, cooling airflow and interlocks, element construction, portable versus outdoor units, power against voltage squared, and testing against wet stacking
A load bank is a test device that applies a controlled electrical load to a power source — a generator set, UPS, battery or transformer — and dissipates the power as heat through resistor elements cooled by fans, so the source can be commissioned, maintained or proven at a known load. Ask three things first: what source, voltage, frequency and kW the bank must load, what step resolution, tolerance and metering the tests need, and whether it will be portable, trailer-mounted or permanently installed, indoors or outdoors.
Resistive (and resistive-reactive where compared) AC load banks for generator, UPS and power-system testing: portable, trailer-mounted and permanently installed units with their load controls. DC battery load banks, electronic programmable loads for laboratories, generator sets themselves (see emergency generator) and dummy loads for RF transmitters are outside this page except where compared.
01
ASCO's data sheet for the Model 2500 (formerly Avtron LPC100) describes an indoor portable resistive load bank of 100 kW with 12.5 kW load-step resolution, three-phase ratings of 240/480 V or 300/600 V at 50/60 Hz, industrial resistor wire elements wound on a mica base and continuously rated at the specified voltage, an overall load tolerance of −0/+5% so that advertised kW is delivered at rated voltage, digital metering of V, A, Hz and kW with data logging, toggle-switch load selection, a 120 V 12 A control supply and a transport case with a 10 ft load cable set. [1]
Its Model 3220 data sheet describes an outdoor static or movable resistive load bank of up to 2,150 kW at 380–480 V (50 or 60 Hz) with 1 kW step resolution, load tolerance within 2.5% of total capacity, stainless-sheathed nickel-chrome elements in magnesium oxide rated up to 800 °C but running below 500 °C, short-term tests allowed up to 10% above rated voltage, and load control from simple switches to a supervisory system; it notes that tests at lower voltage reduce the rating because power is proportional to voltage squared. [2]
Editorial calculation: a bank rated at 480 V run on a 400 V source delivers about (400/480)² ≈ 69% of its rated kW, so a 1,000 kW bank would load the source to about 690 kW; size the bank for the actual test voltage. [2]
Give the supplier the source type (generator, UPS, transformer), voltage, phases, frequency and kW (and power factor if reactive load is needed), required step resolution and tolerance, metering and data logging, control method (local, remote, automatic sequences), portable or permanent installation, indoor or outdoor environment and ambient temperature, cable connection method and length, noise limits, enclosure rating and finish, and quantities.
02
The Model 2500 uses eight fans giving about 2,112 CFM of cooling air, with exhaust temperature sensors interlocked so that load steps are disabled if fans fail, branch fusing for short-circuit protection and a 12 A fused control circuit; the Model 3220 uses two axial fans giving 15 m³/s (31,783 CFM) with vertical discharge and a typical 76 dBA at 3 m, interlocks load contactors with the fans, protects each element group and contactor with an HRC fuse for high fault currents, adds phase-rotation detection on movable units, thermal detectors, an emergency stop, IP54 electrical enclosures and IP1X screens, and is rated for 35 °C ambient (50 °C optional) with an average air temperature rise of 113 °C. [1] [2]
Trystar, a power equipment maker, explains that rarely used or lightly loaded diesel generators suffer wet stacking — unburned fuel and soot in the exhaust — which raises emissions, reduces available power, shortens life and increases maintenance, and that load banks are used to exercise generators so fuel burns completely; it reports that NFPA 110 removed the option of testing below 30% of nameplate for 30 minutes in 2005 and suggests at least 75% load to burn off existing deposits, under professional supervision. [3]
Editorial note: confirm the exercise and testing requirements that apply to your installation from the edition of NFPA 110 or local code adopted by your authority, and size the load bank and test plan to meet them.
03
Simplex, a US load bank maker, explains that a resistive load simulates lighting and heating and the unity power factor component of motor and transformer loads, while inductive load banks add iron-core reactive elements. In its words the inductive load is "typically" rated at 75% of the corresponding resistive load, so that together they give a 0.8 power factor: "for each 100KW of resistive load, 75KVAR of inductive load is provided." With a resistive/inductive load bank, it says, full power system testing is possible, including the effect of reactive currents on generator and voltage regulator performance. [4]
The ASCO data sheets this page already cites describe resistive load banks [1] [2]. Trystar describes load banks used to exercise lightly loaded diesel generators so fuel burns completely, suggesting at least 75% load to burn off deposits [3]. If the test must also show how the generator and regulator handle a lagging power factor, ask for a resistive-reactive unit and its kVAR rating, as Simplex describes [4].
The dynaMITE page lists a UL file number, E151624, PLC control with an 8-inch touchscreen and MODBUS over TCP/IP, and states that fuses are current limiting type, 200KAIC, 600V, "enabling safe use on large generating or UPS system" [5]. Ask any supplier for the interrupting rating of the branch fuses against the fault current at your generator or UPS terminals.
Editorial calculation: 100 kW with 75 kVAR gives an apparent power of √(100² + 75²) = 125 kVA and a power factor of 100 ÷ 125 = 0.8; 1920°F is about 1,049 °C, 1080°F about 582 °C and 120°F about 49 °C. [4]
| Item | Simplex (as published) | Already cited (ASCO) |
|---|---|---|
| Portable resistive rating | dynaMITE Series 300-400kw at 240V and 480V, 3-phase | Model 2500: 100 kW |
| Load step resolution | 5KW (options 1-5-10-25KW) | 12.5 kW (2500); 1 kW (3220) |
| Branch circuits | Not more than 50 KW each; current limiting fuses, 200KAIC, 600V | Branch fusing |
| Element alloy and temperature | FeCrAl; 1920°F max. continuous rating; 1080°F operating; cools to ambient in 10 seconds | Resistor wire on mica base |
| Cooling interlock | Intake temperature switch set at 120°F | Exhaust temperature sensors interlocked |
| Enclosure for fixed units | NEMA-1 indoors; NEMA-3R outdoors | IP54 electrical enclosures (3220) |
| Reactive option | 75KVAR inductive per 100KW resistive for 0.8 power factor | — |
Values are from Simplex's load bank fundamentals and dynaMITE pages; Simplex's brochure PDF was not reviewed.
04
The companies in the manufacturer list below show this product on their own websites. Confirm the legal seller, factory and scope for your order.
05
This is a functional reference built from the sources cited; it is not one maker's design.
| Part | Role | Fix in the order |
|---|---|---|
| Resistor elements | Turn power into heat. [1] [2] | Type, rating, voltage. |
| Load contactors and steps | Switch load in increments. [1] [2] | Step resolution. |
| Fans | Cool the elements. [1] [2] | Airflow, discharge direction. |
| Interlocks and sensors | Prevent load without cooling. [1] [2] | Fan, temperature, phase rotation. |
| Fuses | Protect element groups. [1] [2] | Type, rating. |
| Controls and metering | Apply and record load. [1] | Local, remote, logging. |
| Enclosure | Protects equipment and people. [2] | IP rating, frame, finish. |
06
A load bank quotation needs values for your power sources and tests. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Rating (kW) | 100 kW portable; 300-400 kW portable; up to 2,150 kW outdoor in one range. [1] [5] [2] | Rating at your voltage. |
| Voltage | 240/480, 300/600; 380–480 V. [1] [2] | Voltages and frequency. |
| Step resolution | 12.5 kW; 5 kW; 1 kW. [1] [5] [2] | Steps available. |
| Tolerance | −0/+5%; ±2.5%. [1] [2] | Guaranteed tolerance. |
| Cooling | 2,112 CFM; 15 m³/s. [1] [2] | Airflow and clearance. |
| Ambient | 35 °C standard, 50 °C option in one range. [2] | Ambient rating. |
| Noise | 76 dBA at 3 m in one range. [2] | Noise at your boundary. |
| Enclosure | IP54 electrical enclosures in one range. [2] | IP and installation. |
| Power factor | Resistive = unity; with 75 kVAR per 100 kW inductive, 0.8. [4] | Resistive or resistive-reactive; kVAR. |
07
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Source: [generator; UPS; kW; voltage; frequency] Load: [resistive or reactive; steps; tolerance] Control: [local; remote; logging] Installation: [portable; trailer; permanent; indoor or outdoor] Site: [ambient; noise; cable route] Supply: [quantity; warranty; service]
These companies list load bank on their own websites.
Its website lists “Resistive Load Banks”.
Product scope checked 2026-10-12
Its website has a product page for load bank.
Product scope checked 2026-10-12
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
To exercise it at a known load so fuel burns completely, preventing wet stacking that raises emissions and reduces power and life. [3]
Its power falls with the square of voltage, so the kW applied drops; size the bank for the test voltage. [2]
Fan and temperature interlocks disable the load steps when cooling is not proven. [1] [2]
Simplex explains that a resistive load bank tests at unity power factor, while adding an inductive load rated at 75 kVAR per 100 kW resistive gives a 0.8 lagging power factor so the generator and voltage regulator can be tested with reactive current. [4]
Sources checked 2026-10-12. The ASCO data sheets describe one maker's load banks and the Trystar article another maker's view of generator testing; code requirements for your installation must come from the adopted standard, and ratings from the supplier offered.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
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