UL Question for VFD panel

Customer has built a panel w/ two vfds. All that is in the box is the two vfds.

Each VFD is fed from a Breaker outside of the box.

Assuming the wire and breaker size is correct feeding the line side of the VFD do I need any additional protection inside the box?

I copied this from the UL website...

"Protect VFDs in accordance with Markings
Variable frequency drives may or may not be provided with a motor overload function and branch circuit protection."

What question should I ask the Drives group at Schneider Automation?

I'm not an expert of the rules but i know you can have a separate panel feeder going directly to another unprotected panel when it is on the same level(or room... not sure) with a short wiring.
But in your case, if you have 2 differents switch going to the same panel it's to my opinion a bad pratice for a safety reason...You could shut 1 down and believe you're safe to work while their still have dangerous power inside the panel...You should have got 2 different drive panel but at least make sure to have signs on the door and inside saying their is more than 1 live power source to the panel.

If you have a common power feeder for both drives...you aren't protecting the drive but just the cable if both can run toghether. Again i don't know if it is a rule or just a good practice but you should have a separate protection for each. In the case only one can run at the time, you could have the main protection small enough to protect the drive...

I like to use high speed semiconductor fuses that it is suppose to blow before all the electronic inside the drive blow but it is more expensive...

I would be more concerned that you can not isolate the 'Box' with one isolator.
the Idea of two seperate CB supplies - I assume from a SWB remotely.
is not good.
As far as motor overload - the operation of the invertor itswelf allows for very accurate current / load status monitoring.
However with larger motors thermistor protection is recommended,

UL - sorry not qualified to assess this.

not bad two answers at the same time with the same concerms

Ok, what if there is just 1 VFD in a Hoffman or Rittal Enclosure mounted on the wall. Does it have to have a door disconnect, CB inside, Motor Overload protection added, etc. to meet UL508A requirements?

A built in VFD overload is fine
For everything else you should probably hire a Certified UL panel builder to do it for you. You will make sure every rules is followed...

the question was raised because the two ul panel builders that quoted the job have a different opinion on the matter.

From a more practical viewpoint "Customer has built a panel" means it's their problem not yours.

As an OEM, it is MY responsibility to make sure I provide UL'd equipment when a customer requires it. What a customer does in their own facility is their responsibility.

The UL requirements are NOT the same as NEC requirements. Your question are more related to the NEC, which DOES tell you what is needed as far as motor protection. Most modern VFDs provide adequate short circuit and overload protection, but you're still required by code to have a means of disconnect, which needs to be within sight of the controller.

As I said - cant help you with UL.
Door interlocking or CB supply there is a matter with what specifications
you want to set.
Electrically (here) The panel needs a lockable isolator.
The access to the panel should be by some key method that prevents easy openning.
there is an option of locking the door with the isolator.
Hoffman or Rittal enclosures are suitable

what is the size of the drive?

ganutenator said:

Ok, what if there is just 1 VFD in a Hoffman or Rittal Enclosure mounted on the wall. Does it have to have a door disconnect, CB inside, Motor Overload protection added, etc. to meet UL508A requirements?

Click to expand...

This answer is easy. 1 VFD in a box and UL 508 does not apply (they can't put a sticker on it):

1.3 This equipment consists of assemblies of two or more power circuit components, such as motor
controllers, overload relays, fused disconnect switches, and circuit breakers, or control circuit
components, such as pushbuttons, pilot lights, selector switches, timers, and control relays, or a
combination of power and control circuit components, with associated wiring, and terminals . These
components are mounted on, or contained within, an enclosure, or are mounted on a sub-panel

Click to expand...

Note, bold & underline are my additions...

I second other people's concerns. There are notes that can cover external disconects (60.1) and multiple disconnects (55.4) but I don't believe there is anything that covers multiple external disconnects. If you really want to know have your certified builder ask UL for a clarification or have them ask their inspector (if they have a good relationship with them).

Of course, if you put the other stuff in the box (disconnect, short circuit protection, etc) then you have at least two items and you could review the design and build to see if it can be listed.

Is it for mechanical and/or higher Degrees of protection (IP??/NEMA??)?
Or, what is the point if they have installed on the wall without the box?
Are they -even so- cabled directly to VFDs without terminals?
Cooling ventilation?

ganutenator said:

the question was raised because the two ul panel builders that quoted the job have a different opinion on the matter.

Click to expand...

fine so it's now in your hand, no longer a UL issue
Do you wanna pay for something that works safe and well or save money just because there is no specific rules or a way to pass on the side. Probably the quote with less stuff is cheaper but you'll got what you'll pay for...

I don't know all the details of youre application but if there is 2 drive in 1 box UL 508a must be applied...Even if just 1, you probably need terminals, control fuses and relay in that box ???

To choose between bids, you should have the same product quality level or you're not choosing bidder but quality...

By the way: Is the IEEE rule checked ok for drive inline noise filtering?
Site harmonic noise level need to be evaluated for large VFD installation or it may bring issues...
Same thing for the load side, is load choke needed because of wire lenght, type or motor age ? Saving motors can worth the price of a good choke...