We Buy Your Generator
- Finance Available, on all new generators.
Whether you’re interested in prime or standby power, if your new diesel generator can’t meet your specific requirements then it simply won’t be doing anyone any good because it can put unnecessary stress on the unit and even damage some of the devices connected to it. Unfortunately, figuring out exactly what size of generator you require is often very difficult and involves a number of factors and considerations.
Making a choice amongst single phase, three-phase, KW, KVA, welder, standby or motor starting generators can be absolutely mind-boggling. To prevent such confusion, we’ve decided to write this blog; to help you get a better idea of how the sizing process works and give you some key things to keep in mind. This is not a substitute for a certified electrician, however, which we always suggest talking to before buying, but it should provide you with enough information to get a solid understanding of some of the key things that are involved when choosing a generator.With the latest advancements in the field of electrical engineering, generators are now available in a wide range of sizes. Generators with power supply capacities of 5 KW to 50 KW are readily available in the personal and home use markets, while industrial generators are anywhere from 50 KW to over 3 Megawatts.
Handy and portable gensets are available for homes, RVs and small offices, but larger businesses, data centres, buildings, plants, and industrial applications need to use the much larger sized industrial generators to meet their higher power requirements.Many people believe smaller generators can be used for standby electric power, because they are not running all the time. Not only is this a myth, it can be very detrimental to your generator. Unfortunately, generator under-sizing is one of the most common mistakes committed by buyers.
Not only does it involve the risks of damaging your new asset; it can also damage other assets connected to it, create hazardous situations and even limit the overall productivity of the business/person relying on it. If nothing else, the key thing to remember here is that more is always better than less.While there is no substitute for having a certified electrician perform an inspection and calculate everything for you, the guidelines below do offer some great starting points and should at least get you started in the right direction:
Know Your Requirements:
Purchasing a generator without understanding your specific power needs can lead to inefficiencies, overspending, or even failure to meet essential power demands. Before investing in a generator, it’s crucial to thoroughly assess your power requirements. Here’s how you can do it effectively:
Itemise Your Power Needs: Begin by compiling a comprehensive list of the electrical devices, tools, appliances, and equipment that you intend to power with the generator. Consider both essential items and those with occasional or intermittent usage.
Determine Starting and Running Wattage: Each electrical device has both starting (surge) wattage and running (continuous) wattage requirements. These values indicate the initial power surge required to start the device and the sustained power needed to keep it running. You can typically find this information on the identification plate or in the owner’s manual of each device.
Calculate Total Power Requirements: Once you have gathered the starting and running wattages for all the items on your list, calculate the total power requirements in either kilovolt-amperes (kVA) or kilowatts (kW). This total represents the minimum power output your generator should be capable of delivering to meet your needs.
Finding Starting and Running Wattage:
Ensuring accuracy in calculating power requirements necessitates obtaining precise starting and running wattage values for each device. While this information is often readily available in the device’s documentation, it’s crucial to locate it accurately. Check the identification plate or refer to the owner’s manual included with each device to find the required wattage values.
Ampere to Watt Conversion:
In some cases, the power requirements of tools may be provided in amperes rather than watts. Converting amperes to watts allows for consistent measurement and comparison of power needs across devices. You can use the following calculation to convert amperes to watts:
Watts
=
Volts
×
Amperes
Watts=Volts×Amperes
For further assistance in properly sizing a generator to meet your exact requirements, our expert team at Bellwood Rewinds is here to help. Feel free to reach out to us at 01429 264097 to speak with one of our knowledgeable representatives. Alternatively, you can submit your inquiry via our online contact form, and we’ll get back to you promptly.
Ensuring that your generator is appropriately sized for your specific power needs is essential for maximising efficiency, performance, and reliability. By taking the time to understand your requirements and seek expert guidance when needed, you can make a well-informed decision that meets your power generation needs effectively.
Choosing the correct generator size isn’t just about avoiding power cuts — it’s about efficiency, performance, and long-term cost savings. An undersized generator will be forced to run at full capacity constantly, increasing wear and shortening its lifespan. On the other hand, an oversized unit may seem safe, but it can waste fuel, increase emissions, and cost more upfront than necessary. By accurately matching your power requirements to the generator’s capacity, you maximise fuel efficiency and reduce maintenance costs over time. Always consider both your start-up and running loads to get the right balance between reliability and affordability.
Many businesses underestimate how easily sizing mistakes can happen. One common pitfall is failing to account for start-up currents — some equipment, like compressors or pumps, draw two or three times their running load when starting. Another mistake is ignoring future expansion; your site might grow, and your power needs can grow with it. Guesswork or using outdated load estimates can lead to a generator that’s either underpowered or unnecessarily large. It’s also a mistake to overlook local regulations on standby systems. A professional site survey and accurate load calculation will help you avoid these costly errors and ensure your investment truly meets your needs.
One often overlooked aspect of generator sizing is load management—strategically controlling which equipment runs at specific times. Not all devices need to be powered simultaneously. By staggering startup or running loads, you can reduce the total power requirement and potentially opt for a smaller, more fuel-efficient generator. For example, lighting, HVAC systems, and heavy machinery can be prioritised or cycled to avoid overwhelming the generator. This is especially helpful for businesses that operate in phases or cycles. Bellwood Rewinds can help you evaluate whether load management could reduce your generator size requirements, saving on upfront costs and long-term fuel consumption. We can also recommend generator controllers and load shedding systems that automatically regulate usage based on your needs. With proper planning, you won’t just choose the right size generator—you’ll get a smarter, more cost-effective power setup that meets both current and future demands.
When choosing a generator, it’s important to understand the sizing strategies behind portable versus standby units. Portable generators are generally smaller and suited for powering a select number of appliances, tools, or temporary setups. They’re ideal for short-term use at home, on-site work, or events. These require accurate load estimation to avoid overloads. Standby generators, on the other hand, are permanently installed and automatically activate during outages, often supporting entire buildings or operations. They must be sized not only for total load but also for peak surge capacity and potential future growth. At Bellwood Rewinds, we help customers evaluate the trade-offs between mobility and capacity, ensuring you choose the right type and size for your scenario. Whether you’re protecting your home from blackouts or powering a factory floor, getting the right generator class and size is essential for safety, performance, and peace of mind.
While online calculators and rough estimates can be helpful starting points, working with an expert ensures you get a solution tailored to your actual site conditions. A professional will assess every aspect of your operation, including peak loads, future expansion plans, and the types of equipment you use. They’ll also consider local compliance requirements and installation constraints that could affect your final choice. At Bellwood Rewinds, our experienced team helps businesses of all sizes select the right generator the first time. With our advice, you’ll avoid unexpected costs, minimise downtime, and ensure your generator delivers maximum performance when you need it most.
As we move through 2026, making the right decision about generator sizing has never been more important, whether you’re planning for emergency backup power at home, supporting commercial operations, or powering outdoor events and construction sites. With advances in generator technology and an expanding market of trusted manufacturers, understanding both your power requirements and the strengths of different generator brands can help you choose the most reliable and cost-effective solution for your specific application.
When sizing a generator, the fundamental principle remains the same: accurately determine the total load you need to support, including any starting surge currents from motors or heavy equipment, and allow a safety margin so that your unit isn’t running at its limit. Your total load should always be expressed in kVA, the standard rating used across UK generator specifications, and it should factor in running and peak loads to ensure stable performance without overloading the system. This approach helps prevent trips, inefficiency, and premature wear while ensuring your generator delivers the output your site requires.
In 2026, the generator market continues to be shaped by manufacturers with strong engineering legacies and reliable product ranges. Pramac remains a widely respected choice for both portable and standby generator applications, combining European build quality with models ranging from compact units to larger industrial sets. Its reputation for robust alternators and intuitive control systems makes it suitable for domestic backup as well as commercial and outdoor project use, and the broad range of available outputs makes matching a unit to a site’s needs far easier.
Alongside Pramac, brands such as Cummins, Honda, Yanmar and Perkins continue to play major roles in the UK market. Cummins generators are known for their heavy-duty performance and are often chosen for commercial, industrial and prime power applications where long hours of continuous duty are required. Honda generators remain a popular option across the portable category thanks to their reliability, fuel efficiency and low-noise operation, particularly where mobility and ease of use matter.
Yanmar and Perkins both have long-established reputations in diesel engine manufacturing, and their generator sets are frequently selected for high-demand or long-run environments such as agriculture, construction sites and industrial power support. Their engines are well regarded for durability, torque and the ability to perform reliably under varied and often challenging conditions.
At Bellwood Rewinds, we encourage customers to consider not only the kVA rating but also how a generator will perform in real-world conditions. Fuel type, serviceability, noise levels and efficiency all vary between brands and models, and these differences can have a noticeable impact on ongoing operating costs and daily usability. Our team can help assess these factors based on your intended application and recommend a generator that delivers performance, reliability and long-term value.
Incorporating knowledge of leading manufacturers and a clear understanding of your load profile will ensure that, throughout 2026 and beyond, your generator choice provides dependable, efficient and practical power for whatever you need it to support.