Blower Fan Fusing with Decentralized VFD

[Engineerist]

Hello Gents/Ladies,

First time post. I wanted to do a sanity check on an electrical layout that I will be building. I want to be sure that this is compliant with NEC standards.

-.5HP Induction Motor with single phase blower fan(Fan is always running and is wired separetely at 200-240VAC)
-Decentralized VFD with built in fusing and disconnect

In order to wire in the blower fan, I will be connecting to the VFD internal output fuse block at the L2 and L3, then inline fusing each conductor going to blow fan.

Is there another way to do this?

Do I need to fuse both conductors?

Is this compliant?

Thanks in advance!

 

[ptonsparky]

Hello Gents/Ladies,

First time post. I wanted to do a sanity check on an electrical layout that I will be building. I want to be sure that this is compliant with NEC standards.

-.5HP Induction Motor with single phase blower fan(Fan is always running and is wired separetely at 200-240VAC)
-Decentralized VFD with built in fusing and disconnect

In order to wire in the blower fan, I will be connecting to the VFD internal output fuse block at the L2 and L3, then inline fusing each conductor going to blow fan.

Is there another way to do this?

Do I need to fuse both conductors?

Is this compliant?

Thanks in advance!

Try explaining what you are planning again. I’ve missed it.

 

[Engineerist]

My mistake, I will clarify.

Induction motor has a built in cooling blower fan that needs to be powered separately. I am using a standalone VFD with its own internal disconnect and fusing.

The goal is to power the blower fan as a branch circuit from the VFD and stay compliant. The blower fan is powered by a single phase 200-240VAC.

My plan was to branch off L2, and L3 from the main fuse internal to the VFD. The branch circuit conductors would both have additional inline fusing and allow for powering the blow fan.

Questions were:

Is there a more effective method of achieving this?

Do both conductors need fusing?

Thanks in advance.

 

[petersonra]

My mistake, I will clarify.

Induction motor has a built in cooling blower fan that needs to be powered separately. I am using a standalone VFD with its own internal disconnect and fusing.

The goal is to power the blower fan as a branch circuit from the VFD and stay compliant. The blower fan is powered by a single phase 200-240VAC.

My plan was to branch off L2, and L3 from the main fuse internal to the VFD. The branch circuit conductors would both have additional inline fusing and allow for powering the blow fan.

Questions were:

Is there a more effective method of achieving this?

Do both conductors need fusing?

Thanks in advance.

I think you are saying you want to tap off the line side of the VFD to power the blower. This is generally NEC legal.

Presumably the VFD input is 240 3 phase. All ungrounded tap conductors would need OCPD.

I would be controlling the blower off a motor starter controlled by an output from the VFD that comes on when the VFD is running.

It seems odd to me that a 1/2 HP motor would need to have a blower added to it.

 

[Engineerist]

The application is low RPM and intermittent duty cycles that can lead to high dissipation of heat. Would a motor starter be an overkill for a 50W blower?

 

[Jraef]

I would use a small IEC style manual motor starter for the blower with an aux contact wired to the VFD enable circuit so that if the blower trips off, it shuts down the VFD. With just fuses, a blown fuse on the blower would not stop the VFD and you might smoke your motor.

 

[Engineerist]

The VFD does monitor motor thermistor input to prevent from overheating.

 

[paulengr]

Manual motor starter. Need both overload and short circuit protection sized to the motor. This also gives you a convenient disconnect and a shutoff signal to the VFD. Most VFDs also have their own temperature monitoring.

 

[Jraef]

The VFD does monitor motor thermistor input to prevent from overheating.

That's kind of like the light on your car dashboard that tells you that your engine has ALREADY over heated. By the time it comes on, you have already caused damage, which is why they call those "idiot lights"...

 

[petersonra]

The application is low RPM and intermittent duty cycles that can lead to high dissipation of heat. Would a motor starter be an overkill for a 50W blower?

they are pretty cheap.