I recently read a piece from Schneider that claimed that new UL rules on SCCR testing us going to require a VFD to have line reactors to get a 65kA rating. In fact, this is what their literature says.
I contacted the regional VFD guy for Schneider and he confirmed this.
Any one else hear anything at all?
Apparently it has to do with the way the new testing will be done.
They have been beating this drum for a couple of months now, based on a paper they published last year. There must have been some national sales meeting recently where all of their specialists were given their marching orders for the coming year, telling them to raise doubts in the minds of customers. The paper they link people to is really involved and complicated, then they make this statement:
... some VFD manufacturers specify that if the transformer power rating is 10 times (or some other ratio) larger than the VFD power rating, then a line reactor must be used. VFD manufacturers may require a line reactor if there is low line impedance defined as less than 1% line reactance. While these methods can be applied to Schneider Electric VFDs also, we believe the information that we are providing is much clearer and easier for customers and installers to use.
This "
easier for customers to use" statement comes near the end of 6 previous pages of formulas and conditions they recommend that people look into. The 10x the kVA rating issue is just a rule of thumb that has been around for decades, long before SCCR ratings were required (which by the way, only applies to VFDs that do NOT have DC bus chokes, it's 20x if they do). But that has nothing to do with attaining the SCCR rating or not. Also in that paper, they imply that a new UL standard for VFD SCCR testing, UL 61000-5-1, is forthcoming. There is no such thing, in fact that is the IEC standard for EMC compliant installation of power conversion equipment, which would include VFDs, but it has nothing to do with SCCR ratings at all.
What I have heard is coming (in 2017 or 2018) is that those IEC EMC requirements are going to tighten up, possibly requiring that VFDs include either line reactors or DC chokes in order to qualify, rather than what we do now which is to offer "EMC filter kit" add-on options as a "parallel" solution, meaning it is connected in parallel with the VFD to immediately absorb any EMI that the drive reflects into the incoming line. The new rules are essentially going to require a "series" solution to electromagnetic emission compliance so as to remove the "skill of the installer" issue with regard to EMC. For companies who are selling mainly in IEC countries where EMC is a huge issue, that means redesigning their VFDs. I don't really know all the details on the IEC changes, it doesn't really affect me. But it may be that Schneider is starting to prep the US market to be ready for a wholesale change in their product design because of this, but don't want to say it's for EMC issues because most people in North America don't care. We do care about SCCR however, so if they make it sound as though that's the reason, it might make it more palatable. Just a hunch though, based on their "Freudian slip" of dropping that IEC EMC spec number as if it is a UL SCCR standard.
The UL testing standard for VFDs is covered under UL508C, which was just updated in May of 2013; there is no published discussion of changing that standard to anything new that I am aware of. In those changes in 2013, the only thing they changed regarding SC ratings had to do with drives (usually small) that use Type E Combination Motor Controllers (CMCs as they refer to them, those little IEC motor protectors) as the sole Branch Circuit Protective Device. They added more stringent testing of those combinations, and disallowed the use of fuses to overcome the problems of using versions of CMCs that had lower SC ratings than the available fault current to try to attain a higher rating. What I heard was happening is that some Asian (Chinese) VFD bottom feeder mfrs were attaining an SCCR rating using their equally cheap junk Type E CMCs, but using fuses in series to pass. So they had a Type E CMC rated at 5kA, followed by a current limiting fuse rated at 200kA, feeding a VFD rated at 5kA, and the bottom feeders were claiming testing at 65kA SCCR to make their products market ready. So UL had to add specs eliminating that possibility. Given that many of the small Schneider ATV 30 series drives are made in China now, it was going to affect them as well.
Side note / tangent: there IS in fact a completely separate change coming to the VFD world in January that will affect anyone in the US wanting to export machinery outside of this country. Starting in January (15th I think), you will need special permission from the Federal Government (DOD I think) to export a machine with a VFD on it that allows the user to program the motor output frequency to be higher than 590Hz. Even if you are not USING it at that frequency, the VFD has to comply with not being able to be REPROGRAMMED to run at above 590Hz. The reason is, those higher frequencies are necessary for certain types of weapon production processing, so they are forcing VFD mfrs around the world to install code that prevents the drives from being re-purposed. For most mfrs it will just involve a firmware change, and if the VFD is used domestically, nobody cares. But if a machine OEM wants to export a machine and it has a VFD on it, they will need a certificate from the Feds stating that the VFD has been hobbled into compliance with that firmware. It's not just the US by the way, it's global, but enforcement is left to each individual country.
