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Overload Relays in VFD Circuit

11/23/2015 4:36 AM

Is O/L relay comes inbuilt in VFD or we have to connect externally to trip the motor under overload condition.

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#1

Re: overload relays in VFD circuit

11/23/2015 4:38 AM

A glance through the VFD manual will answer that question, as will a telephone call to the VFD manufacturer. As the name of the manufacturer and the type of the VFD is not known to the forum, the original poster is well advised to try either or both of the above two actions as the quickest route to a valid answer to the question.

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#2

Re: overload relays in VFD circuit

11/23/2015 7:29 AM

Is usually built-in, and if you are controlling two motors at the same time, you must install 2 separate overload relays. But like they said, call the manufacturer.

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#4
In reply to #2

Re: overload relays in VFD circuit

11/23/2015 2:08 PM

Yes, individual motor protection is needed. In some jurisdictions, there may be other choices than overload relays, such as thermal switches inside each motor.

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#3

Re: overload relays in VFD circuit

11/23/2015 10:47 AM

If you are in North America and the VFD is UL/CSA listed, then yes, it has the OL built in, because that is a requirement of attaining those listings, as long as the VFD was manufactured after 2005. But if the drive is not listed by one or both of those agencies, or is older than 2005, then it is not guaranteed and a phone call to the mfr is the best way to ascertain this. Wording in manuals can be confusing and may require a deeper understanding of subtle differences in terminology. Companies that failed to include motor OL protection in their design (because it requires extra testing expense) will often use marketing tricks to make it SOUND as if they cover it.

But as mentioned, even if it is included, it will only be valid for one motor per drive.

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