480 VAC VFD Power - Do I need an Enclosure & Disconnect? 6

[PaulKraemer]

Hi,

I work for an equipment manufacturer. For a machine we are building, I have a VFD for an Exhaust Blower that requires 480 VAC 3-phase 6 amps. The VFD is designed so that it can be mounted on a wall without having to be inside an electrical enclosure. Typically, the exhaust blower is located inside a building. In these cases, I provide a small electrical enclosure with a disconnect switch that I mount on the framework that supports the blower. I mount the VFD externally on the side of the enclosure. Incoming power is run into the enclosure and landed at the disconnect. After the disconnect, power passes through fuses and goes out of the enclosure to the VFD. Aside from the 480 VAC fuses and the disconnect inside the enclosure, I also have one additional fuse, a relay, and a few terminal blocks to support some 24 VDC I/O related to the Exhaust Blower controls. Being the enclosure is so close to the blower, I do not use an additional disconnect between the VFD and the Blower Motor.

On this new project, the exhaust blower will be located outside. Rather than having to obtain a weather-proof enclosure, my customer has told me they will have a climate controlled room within 10-15 feet of the blower location in which I can put my VFD and any other components related to the Exhaust Blower. In addition to my Exhaust Blower controls, this room will contain other controls that support unrelated equipment. Being this room might typically be locked and because it is 10-15 away from the Exhaust Blower, I am planning to provide a disconnect at the blower location to make/break the VFD output power to the Blower Motor.

With the knowledge that this equipment will be in the United States (New Jersey), I have looked through NFPA 79 (Electrical Standard for Industrial Machinery), and I am still not sure how to answer the following questions:

[ol 1]
[li]Am I required to have a disconnect switch for the incoming power circuit (480 VAC)? Or is it allowable to simply land the incoming power circuit at finger safe fuse holders, relying on the fuses as the means by which someone would remove power from the VFD?[/li]
[li]Do the 480 VAC fuses (and the disconnect if I need one) have to be in an enclosure? Or is it allowable to mount these and my 24 VDC components (fuse, relay, and terminal blocks) on an open, wall-mounted panel?[/li]
[/ol]

Any advice will be greatly appreciated.

Thanks and best regards,
Paul

 

[John2025]

IMHO, it needs fuses or CB somewhere and a lockable disconnect within sight. There are some rules about lockable disconnecting means out of sight that I don't remember, but I wouldn't consider it myself. And everything in an enclosure with conduit ( EMT, liquidtite, etc.) Nothing exposed.

 

[dpc]

In the final installation, there must be a local disconnect within sight of the motor "controller", in this case the AFD. In the US (NEC) there is no exception to this. But this disconnect does not have to be integral to the AFD. It could be a standard fused safety switch on the wall next to it. Outside the US, I have no idea.

Cheers,

Dave

 

[GroovyGuy]

hi paul,
in reply to your query above;

Q1) Am I required to have a disconnect switch for the incoming power circuit (480 VAC)? Or is it allowable to simply land the incoming power circuit at finger safe fuse holders, relying on the fuses as the means by which someone would remove power from the VFD?
A1) It depends upon the installation site. (ie many industrial sites do not require a means of disconnect local to the motor. This is typical of most industrial sites that have a trained electrical staff on hand at all times).
Finger-safe fuseholders are not considered as an approved 'means of disconnect'.

Q2) Do the 480 VAC fuses (and the disconnect if I need one) have to be in an enclosure? Or is it allowable to mount these and my 24 VDC components (fuse, relay, and terminal blocks) on an open, wall-mounted panel?
A2) The fuses definitely need to be mounted inside an enclosure.
If you require a disconnect-switch and fuses; I wouldn't hesitate to install the drive inside a disconnect-type of enclosure. This gives you sufficient space to mount the fuses (or CB), interface relays, Customer TBs, CPT (for the enclosure exhaust fan).
Regards,
GG



"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[dpc]

A1) It depends upon the installation site. (ie many industrial sites do not require a means of disconnect local to the motor.

In this case, we are talking about (I think) a disconnecting means at the controller, not the motor. I agree that there are exceptions that allow the local disconnect at the motor to be omitted, but those exceptions do not apply to the required disconnect at the motor controller, in this case the AFD.

 

[itsmoked]

for the enclosure exhaust fan)

With just a VFD in the enclosure I frequently use the VFD's fan as the only fan.

I mount the VFD near the top and make an opening the size of the fan outlet. All VFDs are finger safe where the fan outlet is so this isn't a problem. I include a like sized opening at the bottom of the enclosure screened as necessary. This way 'a fan' which will die eventually doesn't immediately kill the VFD. VFD fans are usually monitored by the VFD and if they fail they shut down the VFD protecting it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

A lockable disconnect ahead of the VFD may be accepted by some inspectors in place of a disconnect "within sight" of the motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[John2025]

You also want the disconnect to be lockable so your customer can comply with lockout/tagout.

 

[jraef]

1. Am I required to have a disconnect switch for the incoming power circuit (480 VAC)? Or is it allowable to simply land the incoming power circuit at finger safe fuse holders, relying on the fuses as the means by which someone would remove power from the VFD?

Yes, you are required to have a disconnect for incoming power. How would someone safely pull the fuses? No fuse holder is suitable for disconnecting power under load (and it does not matter that you don't INTEND on pulling fuses under load, it's assumed that it might possibly happen.)

2. Do the 480 VAC fuses (and the disconnect if I need one) have to be in an enclosure? Or is it allowable to mount these and my 24 VDC components (fuse, relay, and terminal blocks) on an open, wall-mounted panel?

Absolutely must be enclosed, exposed live terminals over 50V are a severe safety hazard.

Not asked, but a possibility (already mentioned):
The disconnect AT THE MOTOR might actually be the thing you can eliminate. If it is an "industrial facility under engineering supervision with established safety protocols and procedures", a lockable disconnect can be out of sight in another area, with the proper signage.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[PaulKraemer]

Hi John2025, dpc, GroovyGuy, Keith, Bill, and jraef -

Thank you all for your very helpful responses. Everyone seems to agree that I most definitely need a lockable disconnect at my VFD location and that my components here should be in an enclosure. This is how I will proceed.

More than one of you have suggested that as long as the disconnect at my VFD is lockable, I may not require an additional disconnect at the motor/blower location. This seems to be dependent on the facility and who might be inspecting it.

Jraef mentioned that this might be the case if it is an "industrial facility under engineering supervision with established safety protocols and procedures" with proper signage. I believe that the facility at which my equipment will be installed will most likely meet this description. I will leave this decision up to my customer. Just for my own understanding, however, I am curious to know which part of which code explains the circumstances under which this would be acceptable. (The facility where this will be installed will be in New Jersey, USA).

I really appreciate all your help.

Thanks again,
Paul

 

[jraef]

430.102(B)(2), exception (b)
The controller disconnect can serve as the motor circuit disconnect as long as it is within sight... with this exception;

In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment

.

It's basically the exception that allows the disconnect handle on an MCC bucket to be considered a valid LO/TO point in a lot of cases (if allowed by the site engineering team).


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[PaulKraemer]

Thank you Jraef - that is a very big help.

Best regards,
Paul