how to parallel generators: A comprehensive guide

March 14, 2025
By BISON

Investing in a generator is a big deal. You must consider many variables, such as the total power requirements of your loads, the power output of the generator, the type of fuel, the flexibility of the fuel (dual-fuel generators), the portability of the generator, and more.

With all these factors in mind, you buy a nice generator and are happy with its performance. But a few years later, your power needs increase, and your existing generator can’t provide the required power.

What to do in this situation? Should you abandon your current generator and buy a new, more powerful, and expensive one? Or are there other options?

It turns out that there is a way that allows you to continue using your current generator without spending a lot of money on a larger generator. The concept behind it is to run two generators in parallel to get the combined power of both generators. If you are not familiar with this concept, read on as we explore how to parallel generators.

In this article, BISON will explain what parallel generators mean and how they work together as a system. We will also focus on the advantages and reliability of parallel generator systems to help you understand all the basics.

What is parallel operation of generators? Or parallel generators?

When we arrange two or more generators so that they supply power to the same load (common load), these generators are said to be connected in parallel. Paralleling is particularly useful in situations where power demand fluctuates, or uninterrupted power is essential. This creates a more robust power source that can scale up or down depending on demand.

Here are some of the key benefits of paralleling generators:

Enhanced power output

No need to invest in one large generator that can be expensive and difficult to maintain. Paralleling allows multiple smaller generators to combine their output to meet your power needs. For example, if you have two identical 2,000-watt generators connected in parallel. Theoretically, you can get 4,000 watts of power from them.

It is a scalable solution that ensures your power system can grow in sync with your needs. This is especially useful for large facilities, industrial sites, and critical operations that require large amounts of scalable power.

Cost

For industries looking to maximize their return on investment, paralleling offers a flexible, efficient, and economically viable solution.

Efficient fuel use: Fuel consumption is minimized by being able to run only the generator needed for the current load. If you have a large generator, its efficiency will be less than 30% when the load is reduced. However, with a smaller generator, the percentage of generator capacity utilization will be higher even at light loads. Therefore, the overall efficiency will be over 80%.
Reduced maintenance costs: Small generators tend to have lower maintenance costs. Also, since both generators share the load, neither generator is stressed and wear and tear is reduced.
Scalability: Purchasing a small generator (preferably the same as your own) will save you a lot of money if your power needs grow. A larger generator will cost more.

Size

Size is also another factor. While residential users may not benefit from it, RV owners and people who use generators while camping will benefit from a small generator (even if they carry two).

Redundancy

If you have two generators in parallel, even if the first generator fails, you will not completely lose power because the other generator is still working. This is especially important in environments such as hospitals, data centers, and emergency systems where power outages are not allowed.

Standards for parallel generators

If you are thinking about connecting and running two generators in parallel, it is more complicated than just hooking them up and expecting them to work.

First, not all generators support parallel operation. So don’t blindly assume that one generator will be compatible with other generators. Support for parallel operation will be mentioned on the generator (or in the official documentation).

Next, we have the electrical characteristics of the two generators. Here, the three important aspects of the generator are frequency, voltage, and polarity (phase).

Voltage matching: All generators must have the same voltage output. For example, both generators should be set to 230V, 400V, or whatever voltage your system requires. Mismatched voltages can damage equipment and create unstable power.
Frequency matching: The generators must run at the same frequency (such as 50 Hz or 60 Hz). Frequency differences can create electrical interference that can harm the system.
Phase matching: The phase angles of the generators must be precisely aligned to ensure smooth power transfer and prevent power surges.

But reality is not perfect, and no two machines produce the same results. Even if you buy two identical generators (from the same manufacturer, model, batch, etc.), their outputs will vary slightly. For output voltage, the difference should be less than five percent. The difference between phase angles should not exceed 5°.

Typically, paralleling is easier when you group identical generators of the same make, model, and capacity together. These generators often come with built-in synchronizing technology to simplify the process. However, modern generators with advanced control panels can also parallel generators of different models or sizes. In this case, more complex synchronizing and load-sharing systems are required to ensure that power is properly distributed between the units.

In some cases, generators using different fuel types (such as diesel, natural gas, or hybrid models) can also be paralleled. This configuration can improve fuel efficiency and operational flexibility but generally requires advanced control systems for stable operation.

How to parallel generators

Once you have verified that the generators are compatible, the next step is to parallel the generators. In this section, we will walk you through the process of paralleling generators to create a reliable power system.

Set up the correct wiring and connections

All wiring should be in accordance with electrical codes and safety standards. If you do not have experience with electrical systems, it is best to consult a professional to perform this step. Be careful to follow these guidelines:

Parallel bus system: Connect the generators to a parallel bus, which acts as a common link to evenly distribute power. This bus ensures that power from multiple generators can be efficiently combined.
Transfer switches: Install transfer switches to safely connect and disconnect the generators from the system or primary load. These switches protect the system from power overloads and unexpected backfeed.
Proper grounding: Ensure that each generator is properly grounded to prevent electric shock and reduce the risk of equipment damage.

Synchronization process

Synchronization is the process of adjusting the electrical characteristics of the generators so that they can operate as a unit. This is a critical step that must be performed carefully to avoid damage. Key aspects of synchronization include:

Voltage synchronization: Ensure that the voltage output of all generators is the same. You can check the voltage of the generators using a meter or electric meter and by adjusting the voltage control setting on each generator. Automatic voltage regulators (AVRs) are standard on modern generators and stabilize the output voltage and make synchronization easier.
Frequency synchronization: The frequency of all generators must be precisely matched. This is achieved by adjusting the engine speed of each generator. A tachometer is usually used to ensure accuracy.
Phase synchronization: Phase synchronization ensures that all generators are aligned so that their waveforms match. An automatic synchronization system or manual synchro checker is usually used to align the phases before connecting the generators to the parallel bus.
Automatic synchronization system: Modern generators are often equipped with automatic synchronization systems that automatically monitor and adjust voltage, frequency, and phase alignment. These systems make paralleling safer and easier, especially when using multiple generators or units of different sizes.

Load balancing

Once synchronization is complete and the generators are running in parallel, the next step is to manage load sharing. Proper load balancing ensures that each generator contributes proportionally to the total power output and prevents overloading of a single unit.

Equal load sharing

Ensures that the total electrical load is distributed between the generators in proportion to their capacity. For example, in a system with two identical 50 kW generators, each generator should handle 50% of the load. In systems where the generators have different capacities, advanced load sharing controllers can distribute the load accordingly.

Monitoring and adjustment

Load sharing should be constantly monitored using the generator control panel or a centralized monitoring system. Any imbalances should be adjusted using the generator’s governor (controls speed) or voltage regulator (controls output voltage). Modern controllers typically handle these adjustments automatically.

Testing the parallel setup

Testing is the final step in any parallel generator setup. Testing ensures that the system is operating efficiently and safely. Follow these steps to test your setup:

Perform a visual inspection: Before testing, confirm that all wiring, connections, grounding, and components are properly installed and meet safety standards.
Perform a no-load test: Start one generator at a time and synchronize them without applying load. Check that voltage, frequency, and phase are properly aligned.
Apply load gradually: After synchronization is confirmed, begin to gradually apply load. Monitor the performance of each generator and ensure that the load sharing is balanced.
Monitor performance: Use the generator control panel or monitoring system to check for abnormal voltage, frequency, or load distribution. Adjust settings as needed.
Safety procedures: Always follow safety protocols during testing. Have appropriate protective equipment and procedures in place to handle any unexpected problems.

If you are using a parallel cable kit, here are some instructions for paralleling your generators

If you have two inverter generators that support parallel operation, you are in luck. These generators will have a sign on the front panel that says “parallel ready” or something similar. They are easiest to run in parallel.

Whenever possible, you need to purchase a generator paralleling kit from the same manufacturer as your generator. This is a special connector kit that helps connect two generators in parallel. The parallel connector has an output socket on the panel that has the output of the two generators combined. Then refer to the generator’s owner’s manual and the instructions for the paralleling kit. Usually they are simply plugged in and they work.

Troubleshooting tips for generator paralleling

While paralleling generators offers significant benefits, there are also some challenges. For the system to operate seamlessly, all components must operate in perfect harmony. Below, we explain some of the most common challenges of paralleling generators and how they can affect your power system.

Voltage mismatch

The generators in a parallel system must have the same output voltage. Any mismatch can result in uneven load distribution, overheating of generator components, or, in severe cases, damage to electrical equipment connected to the system.

Solution:

Make sure all generators are properly calibrated to produce the same voltage before synchronizing. Use an automatic voltage regulator (AVR) to maintain a stable voltage output during operation.

Frequency mismatch

For the generators to work together, their output frequency (usually 50 Hz or 60 Hz) must be the same. Frequency mismatches can cause mechanical stress, surges, and erratic operation.

Solution:

Adjust the engine speed of each generator to ensure the frequency is the same. Modern generators with automatic synchronizing systems automatically monitor and adjust the frequency, reducing the risk of this type of problem.

Uneven load sharing

In a parallel system, generators must share the electrical load in proportion to their capacities. Overloaded generators may experience overheating, fuel inefficiency, and mechanical wear. On the other hand, underutilized generators may waste fuel and not operate efficiently.

Solution:

Use load sharing controllers to evenly distribute the load between generators. These devices continuously monitor the load conditions and adjust each generator’s output accordingly.

Harmonic distortion

Harmonic distortion refers to the disruption of the electrical waveform of the power system, usually caused by generators operating at different specifications or conditions. It can also occur when nonlinear loads, such as electronic devices or variable speed drives, are connected to the system. Harmonic distortion reduces the overall efficiency of the system and can damage sensitive electronic equipment. It can also create noise in the circuits and produce fluctuating power output.

Solution:

Install harmonic filters in the power system to minimize distortion. Also, ensure that the generators have compatible specifications to reduce harmonic interference.

Generator compatibility issues

Paralleling becomes more challenging when combining generators of different sizes, models, or manufacturers. Generators with incompatible specifications may operate inefficiently or fail to synchronize properly, reducing the performance and reliability of the entire system.

Solution:

Ensure that the generators in the system are identical or equipped with advanced control systems. Modern generators are often designed to handle compatibility issues, allowing seamless paralleling of units of different capacities.

Communication failures in control systems

Control systems are critical for monitoring and managing paralleled generators. If the communication system fails (for example, between controllers or sensors), the generators may not operate in unison. Communication errors can lead to poor synchronization, uneven load sharing, and inefficient operation.

Solution:

Perform regular maintenance on the control system to ensure that all equipment is operating properly, and communication channels remain open. A backup communication system can also help reduce the risk of failures.

Conclusion

While paralleling generators offers significant benefits, such as increased power capacity, reliability, and flexibility, it requires high-quality equipment and proper setup. Issues such as voltage, frequency mismatch, or load imbalance can affect the overall performance of the generator system and, if not resolved, can result in costly repairs or downtime.

As a leading professional generator manufacturer in China, we offer a wide range of high-quality generators and accessories designed for efficient paralleling and unmatched performance. Whether you need a generator for industrial use, critical backup power, or remote operation, our products deliver reliability and durability. For complex setups, consulting the BISON professional team can help avoid these challenges and ensure your generator system operates seamlessly.