Re: VFD superceeds Motor Starter?

From my experience the most reliable protection for guarding the operator is
a local horsepower rated switch connected upstream of the VFD which will
isolate all ungrounded conductors of the motor load from the energy source
in case of VFD malfunction and as an aid troubleshooting. Then a guy can
open the door on the switch and verify that all the blades are out of the jaws
before you test for for voltage. VFD's are great accessories but they are
absolutely not disconnect switches.
cheers
Denis


-- In CAD_CAM_EDM_DRO@yahoogroups.com, "scyvt" <scy@...> wrote:

>
> Electromechanical motor starters, as have been in general use for at
> least 70 years, offer motor protection from overvoltage, undervoltage,
> and overcurrent. From an operator safety standpoint, perhaps the most
> important feature is no-voltage protection; that is, if there is an
> interruption of power, the machine will not automatically start up
> when power is restored.
>
> Modern electronic VFD's offer all the above functions, plus of course
> variable speed and a raft more. But are they considered as reliable as
> the time-tested electromechanical motor starters as far as guarding
> operator safety? In other words, can I use a VFD alone where a motor
> starter was used before?
>
> TIA
>
> Steve
>