Starter vs. VFD

[anbm]

We have a combination starter/HOA/fused disconnect switch in existing motor control center that serves an fan on roof.
Owner wants to add a VFD to serve same fan, my understanding VFD will act similar as starter. Should
we remove the starter in disconnect (in MCC) once VFD is installed or turn HOA into off position?

 

[Jraef]

We have a combination starter/HOA/fused disconnect switch in existing motor control center that serves an fan on roof.
Owner wants to add a VFD to serve same fan, my understanding VFD will act similar as starter. Should
we remove the starter in disconnect (in MCC) once VFD is installed or turn HOA into off position?

If it were me, I'd leave the starter there, but wire around it directly to the fused disconnect to use it as a feeder direct to the VFD. It's not good to have a contactor / starter opening and closing in the VFD circuit. If you have to have one, the line side is better than the load side, but it's better yet to not have it at all. But I'd leave the starter in there for when you want to service the VFD, so all you have to do is move the wires over.

 

[GearMan]

If it were me, I'd leave the starter there, but wire around it directly to the fused disconnect to use it as a feeder direct to the VFD. It's not good to have a contactor / starter opening and closing in the VFD circuit. If you have to have one, the line side is better than the load side, but it's better yet to not have it at all. But I'd leave the starter in there for when you want to service the VFD, so all you have to do is move the wires over.

I like the way you think!

 

[iaov]

I like the way you think also but am wondering why the VFD. Has something in the process changed that requires the motor to be throttled? Also the poster stated that this starter was in an existing MCC. Throwing a VFD in the same bucket with the starter may not be possible because there usually is not much room in an MCC bucket. If this MCC is just a cabinet with some room I?d leave the starter in place for the same reasons jref stated.

 

[GearMan]

I like the way you think also but am wondering why the VFD. Has something in the process changed that requires the motor to be throttled? Also the poster stated that this starter was in an existing MCC. Throwing a VFD in the same bucket with the starter may not be possible because there usually is not much room in an MCC bucket. If this MCC is just a cabinet with some room I?d leave the starter in place for the same reasons jref stated.

Remote VFD is how I took it.

 

[iaov]

Could be. To qoute HS Thompson "First we must study its habits"!

 

[Jraef]

Remote VFD is how I took it.

That's how I interpreted it as well. 99.9% of the time, it's a given that a VFD will not fit in an MCC bucket that housed the same size FVNR starter.

Anbm,
Something I may have missed from your initial question however was the "... VFD will act similar to a starter" aspect. The answer is yes, modern VFDs will in that they provide all of the motor protection and on-off control necessary, just as a starter does. But if your owner buys some old cheap piece of junk from fleabay, that may not be the case. Some older drives needed an external overload relay so be careful if he goes that way. it's a bad idea for other reasons as well and if he is considering it, post back and we'll five you ammo on why he shouldn't.

 

[Besoeker]

If it were me, I'd leave the starter there, but wire around it directly to the fused disconnect to use it as a feeder direct to the VFD. It's not good to have a contactor / starter opening and closing in the VFD circuit. If you have to have one, the line side is better than the load side, but it's better yet to not have it at all. But I'd leave the starter in there for when you want to service the VFD, so all you have to do is move the wires over.

We are routinely required to fit a contactor with VFDs. And usually on the load side.
It's a safety matter. If someone hits the emergency stop, then there is a requirement for a physical disconnect between the supply and motor.
It isn't a mandatory regulation to comply with legal requirements (AFAIK) but customers write it in to their specifications.
If you want the job, you provide, as far as is reasonably practicable, a spec compliant bid.
Technically, it's not a big issue. An early break contact shuts off the inverter and the contactor does not break current.
And, even if it did, any transient overvoltage would be quenched by the IGBT inverse diodes stuffing it into the DC bucket.

This, typically what we do.

Real drawing from a real project.