Common Mistakes When Buying a Generator — and How to Avoid Them

If you are about to buy the first generator for your company, or if this is the first time you have purchased a generator yourself, don’t worry, help is at hand to make sure you get it right first time.

Generators aren’t cheap, and a purchase can quickly become an expensive mistake if the system is undersized, oversized, installed incorrectly, or poorly matched to your site’s requirements. Many businesses only discover issues when the generator fails under load or burns more fuel than expected.

To help you avoid costly errors, here are the most common mistakes organisations make when purchasing a diesel generator — and exactly how to avoid them.

1. Choosing the Wrong Power Output

The mistake:

Buying a generator based on guesswork or headline kVA figures without accurately calculating your load.

Why it causes problems:

• Undersized units can overload, damage equipment or fail to start large motors.
• Oversized units waste fuel, carbonise engine parts and add unnecessary cost.
• Efficiency depends on more than age or model — it hinges on correct load matching.

How to avoid it:

• Calculate your running and starting load (kW/kVA).
• Add a safety margin for motor start-up currents.
• Ask a critical-power engineer to validate your calculations.

Correct sizing is the single biggest factor affecting long-term reliability. It’s a false economy to go it alone.

2. Misunderstanding the Generator’s Purpose

The mistake:

Buying a generator without clearly defining what it will power and how often it will run and how long it needs to run for.

Consequences:

• Equipment may receive too little power or unstable supply.
• Excess capacity increases running costs.
• Sensitive electronics can be damaged if incorrectly matched.

How to avoid it:

• List all equipment the generator must support.
• Identify whether your usage is light commercial, industrial, or mixed.
• Check the generator’s kVA (or MVA for very large sets) is matched to both your peak and continuous load.

The clearer your purpose, the easier it is to choose a safe and efficient system.

3. Overlooking Physical Space and Installation Requirements

The mistake:

Not planning for the generator’s footprint, ventilation or access requirements.

Why it matters:

• Poor airflow leads to overheating and failure.
• Incorrect positioning can violate noise/environment rules.
• Tight spaces make servicing difficult and more expensive.
• Installation could be difficult or impossible if access to your site is inadequate. Roads, gates, doorways, shutters and parking can all impede installation.

How to avoid it:

• Confirm the generator’s dimensions and clearance.
• Ensure ventilation is adequate for cooling and exhaust.
• Consider whether a portable or fixed installation is more appropriate.
  Proper site planning prevents costly installation surprises later.

4. Confusing Standby and Prime Power Ratings

The mistake:

Using the wrong power rating for the wrong job. We think of power requirements in several ways, including standby power and prime power.

Standby power:

• Used during grid failure only.
• Ideal for emergency backup.

Prime power:

• Acts as your main power source.
• Designed for long, regular run times.

How to avoid it:

• Choose standby for occasional outages.
• Choose prime for remote sites or continuous operation.

Using standby units as prime power (or vice versa) dramatically shortens generator life.

5. Ignoring Fuel Efficiency and Running Costs

The mistake:

Assuming all diesel generators consume fuel at similar rates.

Why it matters:

• Fuel is often the biggest long-term cost.
• Inefficient models increase operational spend.
• Poor maintenance increases consumption even further.

How to avoid it:

• Check manufacturer data on fuel burn rates.
• Review the service history of used units.
• Don’t dismiss older models — a well-maintained set can outperform cheaper new ones.
  An efficient generator saves thousands of pounds over its lifetime.

6. Underestimating Noise Levels

The mistake:

Buying a generator without considering the noise impact on staff, neighbours or compliance requirements.

Consequences:

• Noise complaints
• Disruption to work environments
• Fines or forced operational changes in urban areas

How to avoid it:

• Choose canopied or containerised generators for built-up areas.
• Install acoustic barriers if needed.
• Position the generator to minimise vibration and sound travel.

Noise control protects people, equipment, and the generator itself.

7. Forgetting About Maintenance and Servicing

The mistake:

Assuming a generator will simply “run when needed.”

Why this causes failures:

• Fuel deteriorates
• Filters clog
• Coolant and oil levels drop
• Batteries degrade

How to avoid it:

• Schedule weekly/monthly self-checks.
• Carry out quarterly professional servicing.
• Keep detailed service records.

A well-maintained generator is cheaper to run and less likely to break down during an outage.

8. Not Getting Professional Advice Early Enough

The mistake:

Choosing a generator before consulting a critical-power specialist.

Why it matters:

Generators are only reliable when correctly sized, installed, configured and maintained. Errors made at the purchase stage often lead to failures months or years later.

WBPS: Helping You Avoid Costly Generator Mistakes

With over 40 years of experience in critical power, WBPS helps businesses choose, install and maintain diesel generators that meet their operational needs. We support you at every step — from load calculations and design to installation, servicing and long-term maintenance.

Speak to one of our engineers today for expert, impartial advice.