PowerFlex 750-Series: Weird Minimum Enclosure Volume requirements

[Tip DS]

Looking over the technical data for a PowerFlex 755 & noticed they specify a minimum enclosure volume for their drives:

(1)When using a circuit breaker or time-delay fuse with a drive installed in a ventilated enclosure, the enclosure volume must be greater than or equal to the minimum volume specified in this column.

(2)When using a Manual Self-Protected (Type E) Combination Motor Controller, the drive must be installed in a ventilated or non-ventilated enclosure with the minimum volume specified in this column.

Anybody know what this is all about? Why do they care about the enclosure size only when using fuse/circuit breakers AND only when that is done in a VENTILATED enclosure?? Is the first note completely inapplicable for an unventilated enclosure?! Why or why-not?

Do the minimum enclosure sizes multiply with the number of drives installed, or is it without regard to the number of drives installed?

Anything you guys can do to shed a little light on the reasoning behind these requirements would be greatly appreciated.

 

[tom baker]

Heat. All the 750 drives I installed were in ventilated cabinets. If you install a smaller cabinet and the drive fails that would be a warranty issue

 

[Tip DS]

Heat. All the 750 drives I installed were in ventilated cabinets. If you install a smaller cabinet and the drive fails that would be a warranty issue

Yeah, they do make some heat. The thing that REALLY throws me is the way they seem to tie the volume requirement to the type of OCPD and/or controller being employed. That, and the way the second note indicates the enclosure must be ventilated or non-ventilated. (And why do they even mention ventilation, if the drive is agnostic in that instance?? They didn't specify the enclosure must be steel or non-steel. LOL)

 

[petersonra]

I asked an ab product manager once and was told it had to do with some kind of issue with the heat in the cabinet might cause the breaker to trip when it should not. I asked why this did not apply to a fuse and never got anything other than a shrug over the phone.

I was also told once it had to do with heat causing arc flashes with iec style breakers.

I was never happy with either answer.

 

[Jraef]

Starting back in 2015, UL began a process of "aligning" their standards with IEC standards. The first big change came with VFD listings. UL508C, which is the general standard for electrical control components, was rescinded with regard to VFDs in 2022 and changed to UL-61800-5-1, which is now harmonized with IEC standard 68100-5-1. There are numerous changes that this required in the UL listing process, and VFD manufacturers were given until 2022 to make those changes. ONE of those changes was in fact an increase in the minimum enclosure volume requirements for any given amp rating of VFD. Under UL508C the only real requirements were clearances above and below in terms of not restricting air flow, but the new 68100 specs now call for minimum air volumes in the cabinets. This is not unique to A-B, but these rules have been in existence for a lot longer in Europe and Asia, so to us, we have not been seeing changes to European and Asian drive products; they were already like that. A-B is simply the last remaining (major) US designed VFD manufacturer. All of the rest are EU or Asian products that are modified for the US and/or brand labeled from one of those.

Another thing you are going to start seeing now is that ALL VFDs must have high speed fuse protection, regardless of whether they have circuit breakers already. So if you order a VFD with a Main CB in the cabinet, it will ALSO have some very expensive fuses in there. Most of the VFD mfrs are trying to use the least expensive fuses they can pass with, and over size them so that they would (in theory) only blow in the event of a dead short, but the cost, and size, is going to be there no matter what.

If a VFD was already previously listed WITHOUT the new 68100 requirements, they can still keep selling them like that, but there has ALSO been a major change going on for years about what's called RoHS (Reduction of Hazardous Substances), which required all manufacturers to cease the sale of anything with lead, cadmium and other dangerous metals, plus all plastics must be "recyclable", meaning no more FRP (Fiberglass Reinforced Plastic). That's why you have seen so many VFD manufacturers come out with new or redesigned products in the past 10 years. The RoHS issue completed in 2017 after a 10+ year grace period, which is why you have now seen VFDF manufacturers "sunset" their older designs. They can still sell them here in the US, but they CANNOT sell them anywhere else in the world, and it's too costly to not have that market open to you.