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To ensure you get the most from your variable speed drives, best practice has to begin before the drive itself is even chosen. By considering what you need from the drive, where you expect the drive to operate and what other devices you need the drive to work with, you can give yourself the best chance of long-lasting, hassle-free operation. 

What to consider

There are five main areas to consider when choosing and installing a new drive:

Mechanical - Is an enclosure needed for the environment in which the drive is installed?

Input power - What and how stable is the power source?

Motor wiring - What wiring should be considered to power the motor?

I/O - What wiring is installed and routed to control the application?

Fieldbus wiring - How are you going to control and monitor without interference?

Spacing and enclosures

Another thing to consider with spacing is what, if any, gases are present in the environment. Some manufacturing environments will have gases such as hydrogen sulfide or chlorine present. An indication of an aggressive atmosphere is corroded copper within the drive. If you have a drive that has corroded copper, it is recommended to choose a drive with a good IP/NEMA rating and conformal-coated circuit boards. We can help you pick a drive with these characteristics when needed.

Without proper space and therefore ventilation around the AC drive, it will be susceptible to heat damage which is one of the biggest causes of failure for drives. However, some environments will require side-by-side mounting, therefore it will be necessary to choose a VSD that allows this type of mounting.


Input power

It’s critical to understand the power source when selecting an AC drive and what type of power is available, whether single or three phase.

We recommend that you consider the following areas:

Voltage level -  Select the appropriate drive for the voltage and input phase
Transformer configuration - You may need to remove metal oxide varistors or filter caps if the transformer does not have a solid grounded secondary
Power quality - If power quality issues exist, you may need to use a VSD with a direct-current choke or built-in line reactor. Another option is the use of an external reactor or isolation transformer

It’s also important to comply with local and national electrical codes when wiring. As these cables also carry high voltage, it is necessary to keep them away from control wiring, other power wires and motor wiring to avoid inducing voltages in other cables.

Induced voltage

It’s possible for induced voltage from output motor cables that run together to charge equipment capacitors even when equipment is turned off and locked out. It’s incredibly important to remember the points below as failure to run output motor cables separately or use shielded cables or metal conduits could result in death or serious injury
Run output motor cables separately or use shielded cables or metal conduits
Comply with national and local electrical codes for cable sizes
Follow the motoring wiring requirements from the manufacturer

Motor wiring

Review the wire used between the drive and motor. If you are performing a retrofit, it may be necessary to replace the wiring, particularly if you are replacing a motor starter or contactor with a drive. The wire must be correctly sized and designed for the environment it is installed in, just like you would have specified a suitable drive and motor.  Will the wire be in a moist environment? Or is it possible that it will be crushed? All scenarios must be considered to select an adequate cable.

Cables designed especially for variable speed drives will have the necessary conductors for the motor - a ground and shield. Grounding is vital for higher frequency switching drives for safety as it provides a route back to the drive from the motor using single-point grounding. Single-point grounding keeps the high-frequency noise generated between the drive and motor to prevent it interfering with other equipment.

You may also need an output reactor and a dU/dT filter when fitting a drive onto an older motor. This will protect the motor from peak voltages that can happen at motor terminals due to reflected waves.

Control wiring

The control wiring is for digital and analog I/O, fieldbus, STO and encoders and its integrity is critical. It requires shielded cables and separation from power and motor wiring. Should your control wiring need to cross power or the motor, it is necessary to do so at a 90° angle. Ensure the wiring is designed for the signal it carries, current and voltage rating. Use the shield to protect against crosstalk. If you use a remote mounted control panel, remember this cable also needs to be routed away from the power and motor wiring.

Best practice checklist

Always make sure to follow manufacturer recommendations and guidelines for the best installation information and to maximise trouble-free operation. Our checklist below is a handy tool to go through each installation area and make sure best practice is covered depending on how and where a drive is installed. 

If you would like to ask any questions about how to get the most from your AC drive, or any other questions regarding VSDs, don’t hesitate to get in touch with our team at Northern Industrial.