Useful Information During Installation and Commissioning of VSDs

Can I use an RCD with my VSD?

Overview

You can use an RCD, but a Type B RCD may be required. UKCA- and CE-marked VSDs are typically fitted with EMC filters to comply with EMC directives. These filters include capacitors connected to earth, which can create leakage currents that may cause an RCD to trip, depending on the installation and other equipment on the circuit.

Useful Knowledge

• Most VSDs allow the EMC earth connection to be disconnected, or are supplied with it disconnected.
• Type B RCDs are significantly more expensive than standard types, which leads many installers to remove the EMC earth connection.
• Removing the EMC earth connection does not affect the basic electrical safety of the unit, but it may affect EMC compliance.

Recommendation

Check whether the EMC earth connection can be removed on your VSD if required. If it cannot be removed, a Type B RCD should be used.

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Is my VSD fitted with internal fuses?

Overview

VSDs are not normally fitted with internal fuses. They are designed for global use, where protection requirements vary. The product manual will specify the recommended protection devices for each region, including fuse type and rating.

Useful Knowledge

• Fuses may not always be recommended; circuit breakers, including MCBs for smaller units, are often used.
• Protection requirements vary between manufacturers, so existing installations should not be assumed to be suitable.

Recommendation

Always refer to the manufacturer’s manual to determine the correct protection for the mains input. The required fuse type, current rating, and voltage rating will be specified.

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Is my control cabinet big enough?

Overview

VSDs contain sensitive electronic and power components that must not overheat. Each unit is designed to operate correctly when the installation guidelines are followed.

Useful Knowledge

• Most VSDs, except the smallest ratings, use internal fans for cooling, which are essential for correct operation.
• Air is typically drawn in from the bottom and exhausted from the top, so panel ventilation must align with this airflow.

Recommendation

Check the required clearances for the VSD. Minimum distances at the top, bottom, and sides must be maintained to prevent overheating.

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How hot can my VSD get?

Overview

Each VSD has a rated ambient temperature, which is linked to its current and overload capability. There is also a maximum ambient temperature, which typically requires the drive to be derated.

Useful Knowledge

• The rated ambient temperature is typically 40°C, but it can be as high as 50°C.
• Operating below the rated ambient temperature, but above freezing, can extend the lifespan of the unit.
• High-IP enclosures can trap heat, so care must be taken to prevent the temperature from exceeding the rated ambient.

Recommendation

Consider the full range of environmental conditions the VSD may experience. Where possible, install the VSD in a location that allows it to operate below its rated ambient temperature. In cold environments, anti-condensation heaters may be required.

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Is my VSD suitable for dirty environments?

Overview

The VSD IP rating indicates its level of protection against dust and contaminants. IP20 units offer minimal protection and must be installed in a suitable enclosure.

Useful Knowledge

• Conductive dust inside a VSD will lead to failure over time.
• Non-conductive dust can cause overheating and reduce fan performance.

Recommendation

Keep the VSD clean. In dusty environments, install the VSD in a suitable enclosure or in a cleaner area where possible. Positive-pressure ventilation can help, provided good maintenance practices are followed.

Long Read - VSD Environment Protection Guide

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Can I use the VSD keypad as my operator controls?

Overview

Using the keypad on an IP20 VSD requires the cabinet door to be opened. This is not good practice; the required controls should be located on the front of the control panel or directly on the machine.

Useful Knowledge

• VSDs with fixed keypads often have a remote keypad option that can be mounted on the control cabinet.
• VSDs with removable keypads will normally have a remote mounting kit available.

Recommendation

If you want to use the VSD keypad, use a remote keypad or keypad mounting kit. Opening the control cabinet door to operate the unit is not recommended and should be avoided.

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Can I use momentary switches on my VSD?

Overview

Momentary switches can be used on all VSDs, but this is not the default configuration. To use momentary switches, also known as 3-wire control, parameters within the VSD will need to be changed.

Useful Knowledge

• Start/Run switches must have a normally open contact, and the Stop switch must have a normally closed contact. Direction is typically selected using a two-position switch.
• Wiring for 3-wire operation varies from manufacturer to manufacturer, so the connections should not be assumed.

Recommendation

Where available, use our IDS Easy Start Guide to provide the details required for commissioning the VSD in 3-wire control. All VSDs can operate in 3-wire control, but the wiring and parameter changes will need to be identified before commissioning.

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What is the control voltage of a VSD?

Overview

Unlike a soft starter, a VSD does not require an additional control supply. The only supply connection required is the mains input.

Useful Knowledge

• If the VSD control needs to remain powered for communication purposes, a 24 V supply may be required.
• Not all VSDs have an external 24 V input. In many cases, an option card is required to provide this functionality.

Recommendation

If an external 24 V supply is required, do not assume the 24 V terminals on the VSD can be used. In most cases, these are outputs rather than inputs. An option card is usually required unless the VSD specifically states that it has a 24 V auxiliary input.

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What type of overload do I need to select?

Overview

In some cases, VSDs are listed with two kW ratings, for example 5.5 kW / 7.5 kW. This indicates that the VSD is dual-rated, and the rating depends on an internal setting.

Useful Knowledge

• In this example, 5.5 kW is the constant-torque, high-load rating, typically with 150% overload capability.
• 7.5 kW is the variable-torque, normal-duty rating, typically with 110% overload capability, suitable for fans and pumps.
• Most dual-rated units default to the higher overload setting, which should be changed for fan and pump applications.

Recommendation

Determine whether an overload parameter is available on your VSD. If present, it will usually be highlighted in the main parameter set. Ensure the selected overload matches the application.

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What is a parameter, and are parameters important?

Overview

Parameters are critical to the operation of a VSD. Every VSD has parameters that can be accessed using the keypad, and each parameter controls a specific aspect of operation.

Useful Knowledge

• VSDs are supplied with default parameter values that can be adjusted to suit the motor and application.
• Default values vary between manufacturers and product ranges, so essential parameters should always be reviewed.
• Parameters may also be configured using a PC or app, depending on the VSD.

Recommendation

The most important parameters are the motor parameters, which must match the motor nameplate. Incorrect values can lead to unexpected behaviour or tripping. Additional parameters are often available for specific applications and should be used to optimise performance.

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I have the control diagram from my previous VSD – can I copy this?

Overview

A wiring diagram can be very helpful, but it is only useful if the overall operation is known and understood. The purpose of each input must be identified so that this information can be applied to any replacement VSD.

Useful Knowledge

• On all VSDs, the function of inputs and outputs is determined by parameter settings.
• By default, most VSDs operate using at least one digital input for start/stop and one analogue input for speed control.
• When replacing a VSD with the same model, the same wiring diagram can often be used; however, parameter changes may still be required to achieve the same operation.

Recommendation

Identify the function of each input and output required, along with the expected operation of the load. Terminal references on your existing wiring diagram should not be assumed unless the VSD is a direct replacement.

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What motor information does the VSD need?

Overview

The motor nameplate provides the most important information for the VSD. The key value is the motor rated current, which is used by the VSD to ensure the motor is not overloaded.

Useful Knowledge

• Incorrect motor parameters can lead to excessive current being drawn by the motor.
• The motor terminal links must be configured to match the VSD voltage. Incorrect configuration can result in poor torque performance. Delta is lower voltage; Star is higher voltage.

Recommendation

Check which motor parameters are required by the VSD, as this varies between models. If sensorless vector control is required, more motor parameters may be needed compared with standard V/F operation.

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What is the difference between local and remote control?

Overview

Most VSDs use the terms Local and Remote control. Local control refers to operation via the VSD keypad, while Remote control refers to operation via an external source connected to the VSD control terminals, such as a PLC, switches, pushbuttons, or potentiometers.

Useful Knowledge

• Some VSDs power up in Local control, while others power up in Remote. Once selected, the control mode is usually retained.
• Switching between Local and Remote varies by model, for example by dedicated key, selector switch, long press, or parameter setting.
• Some VSDs allow the speed reference and run command to come from different sources.
• A remote-mounted keypad is still considered Local control, as it interfaces directly with the VSD.

Recommendation

Using Local control during commissioning is recommended, as it helps separate control issues from power issues. For normal operation, use remote controls such as a keypad, panel-mounted controls, BMS, or PLC.

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How do I connect my Emergency Stop?

Overview

No VSD manufacturer will specify exactly how to implement an Emergency Stop, as this depends on the application. The installer must understand the machine operation and determine the safest approach.

Useful Knowledge

• Emergency stops are often implemented by removing power to the VSD; however, this results in a coast stop unless a brake is applied.
• Some VSDs provide alternative deceleration ramps that can be used for emergency stopping. These require configuration to achieve the desired stopping performance.

Recommendation

Consult the engineer responsible for safety to determine the correct emergency-stop strategy. Removing power is common, but it may not be suitable for machines with accessible moving parts.

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The motor is going in the wrong direction?

Overview

The VSD will typically operate the motor in the forward direction by default, but this may not match your application requirements.

Useful Knowledge

• Do not assume a new VSD will rotate the motor in the same direction as a previous installation. Always check rotation at low speed during commissioning.
• Some VSDs allow the direction of rotation to be changed via parameters.

Recommendation

Do not set the VSD to reverse simply to match your required direction. Change the motor direction by swapping two of the motor cables on the VSD output. Match the VSD forward direction to the application forward direction.

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Do I need sensorless vector control?

Overview

Sensorless vector control is a feature available in most VSDs that enables higher torque at low speeds. It may be required depending on the application and factors such as static friction, incline, pressure, material viscosity, and gearing.

Useful Knowledge

• Most VSDs are supplied with standard V/F control, which is effective for centrifugal loads such as fans and pumps.
• Sensorless vector control requires an auto-tune. For best results, this should be performed with the motor uncoupled, on a bare shaft. A stationary auto-tune can be used, but it is less effective.
• In V/F control, low-speed torque can be improved by increasing the boost setting in the VSD.

Recommendation

If the motor is mechanically coupled to the load, start by using V/F control to determine whether it is sufficient.

If the load struggles to start, sensorless vector control can be used if increasing the boost setting does not resolve the issue.

When using sensorless vector control, it is essential that all motor parameters are set correctly. For optimal performance, the auto-tune should be carried out with the load decoupled, on a bare shaft. This is why it is recommended to confirm whether V/F control is adequate before decoupling the load.

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