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Power Transmission Distributors Association is...

the leading association for the power transmission/motion control industrial distribution channel, bringing together distributors and manufacturers.

Resources | Product Training | PT/MC Tech Tips | Controls & Sensors

Tech Tip: Controls & Sensors

Enhance your employees’ product and industry knowledge with PTDA’s Tech Tips. This library of online tips, hints and techniques may be used to educate new and current employees on power transmission/motion control (PT/MC) products, technologies and concepts and serve as reference and reminder for more experienced staff. Tech Tips are based on the expertise of PTDA member companies, content from Motion Control Made Simple or PTDA’s Power Transmission Handbook®, the definitive resource and training tool on PT/MC products.


Visit the full library  of Tech Tips for additional products.

Do VFDs have a service factor?

The answer is no. VFDs have a very specific maximum continuous output ampere rating limit without a safety factor allowance for additional continuous output amps. Note that VFDs do have a published 60 second overload rating as a percentage of the VFD's continuous output ampere rating. Variable torque or normal duty VFDs can supply 110 (or 120) percent of continuous output ampere rating for 60 seconds. Constant torque or heavy duty VFDs can supply 150 percent of continuous output ampere rating for 60 seconds as well. Beyond 60 seconds, the VFD will trip (most likely with a VFD Over temperature or Motor Overload code). An attempt by the motor to draw more than these percentage levels will result in the VFD clamping output current by reducing the amplitude and frequency of the power supplied by the motor.  Most VFDs can supply 200 percent current for one or two seconds. A quick attempt to draw a higher level of current will cause the VFD to trip (most likely with an Overcurrent code) cutting off current to the motor.


What six factors affect the proper sizing of VFD?

1. Temperature of the installation site. All VFDs can operate in a 40° C ambient. Some are rate for a 50° C ambient.
2. The ability of the VFD enclosure to dissipate heat. 
3. Total continuous loading on the VFD as a percentage of its rated ampere load capability.
4. Load type: constant torque, variable torque, constant horsepower or impact
5. Single or three-phase input power feed
6. Setting of VFD output power switching frequency. Refer to VFD selection literature for specific guidelines. 

The information provided in Tech Tips is not meant to be all-encompassing, but rather to draw attention to and provide information about the particular subjects covered. All suggestions and recommendations contained in Tech Tips are based upon information that is believed to be accurate to the best of the experience and knowledge of PTDA’s contributing members, but are made without guarantee or representation as to results. PTDA and Tech Tip contributors expressly disclaim any warranties or guaranties, express or implied, as to the accuracy or completeness of any information published in Tech Tips, and disclaims and makes no warranty that the information in Tech Tips will fulfill any of your particular purposes or needs. PTDA and Tech Tip contributors disclaim liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on Tech Tips.