# What causes an overvoltage fault in a VFD unit? How can it be prevented from happening again?

**URL:** <https://forumautomation.com/t/what-causes-an-overvoltage-fault-in-a-vfd-unit-how-can-it-be-prevented-from-happening-again/13944>\
**Category:** Electrical\
**Tags:** vfd\
**Created:** [March 17, 2026, 7:01am UTC](https://forumautomation.com/t/what-causes-an-overvoltage-fault-in-a-vfd-unit-how-can-it-be-prevented-from-happening-again/13944 "2026-03-17T07:01:44Z")\
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**Page:** 1

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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [March 17, 2026, 7:01am UTC](https://forumautomation.com/t/what-causes-an-overvoltage-fault-in-a-vfd-unit-how-can-it-be-prevented-from-happening-again/13944/1 "2026-03-17T07:01:44Z")

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# Overvoltage Fault in VFD (Variable Frequency Drive)

## Causes of Overvoltage Fault

## Regenerative Energy

During motor deceleration, energy flows back to the **[Variable Frequency Drive (VFD).](https://forumelectrical.com/working-principle-of-variable-frequency-drive-vfd/)**

This increases DC bus voltage → trips on overvoltage.

## Fast Deceleration Time

Sudden stopping → high energy return → voltage spike.

## High Input Supply Voltage

Supply voltage higher than rated → DC bus exceeds limit.

## Faulty Braking Resistor / Unit

Braking system fails → excess energy not dissipated.

## Load Inertia (Heavy Loads)

High inertia loads (fans, conveyors) generate more regenerative energy.

## Voltage Spikes / Surges

**[Lightning](https://forumelectrical.com/lightning-arrester-testing-procedure/)** or switching surges increase input voltage.

 ![image](https://cdn.forumautomation.com/original/2X/b/bf0f5110dd8a8be74a1e57427514c175e1cc9f59.jpeg)

# How to prevent Overvoltage Fault?

## 1). Increase Deceleration Time

Slower stopping reduces regenerative energy.

## 2). Install Braking Resistor

Dissipates excess energy as heat.

## 3). Use Dynamic Braking Unit

Controls DC bus voltage effectively.

## 4). Use Regenerative VFD

Sends excess energy back to supply instead of tripping.

## 5). Check Input Supply Voltage

Ensure voltage is within limits.

## 6). Install Line Reactor / Surge Protection

Reduces spikes and harmonics.

## 7). Proper Load Selection

Avoid sudden stopping of high inertia loads.

**[Overvoltage](https://forumelectrical.com/what-are-the-steps-to-test-overvoltage-and-undervoltage-protection-relays/)** in a VFD occurs mainly due to regenerative energy during the motor deceleration, high input voltage (or) braking system failure.

It can be prevented by increasing deceleration time, using braking resistors or regenerative drives and ensuring proper supply voltage and surge protection.

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