A few years ago, UL rescinded the listing of new VFDs under UL-508C and replaced it with UL-61800-5-1, which changed the way short circuit testing of the VFDs is done and what it takes to pass. Under the old standard, the VFD did not have to consider the possibility of a line-to-load failure because the possibility was s extremely rare that under that old standard, UL felt it was not a significant risk. But the new standard has adopted the IEC testing requirements, which do require testing further possibility. That is why new drives are not required to have additional short circuit testing, generally resulting in the inclusion of high speed fusing. Drives that were previously listed under the old UL-508C can remain listed, but as they age out, their replacements will have to pass listing under the new standard. This standard was released back in 2012 and manufactures were given 10 years to affect the changes. That time was up in 2022 and now all drives released since then are going to have to conform.
The reason I bring this to everyone’s attention is twofold: understanding what is coming or has changed, and to point out that any drives still showing that they “don’t need anything” are at best, of a design over 10 years old and likely headed for obsolescence. So that should be taken into consideration when selecting a drive for a new installation.
Bottom line: any device in a circuit needs short circuit protection and per NEC rules, that must be in accordance with the manufacturer’s listing and instructions. But if a drive says it does not need fuses or is not specifically listed with a specific circuit breaker ahead of it, it is either not listed at all, or not long for this wor
A few years ago, UL rescinded the listing of new VFDs under UL-508C and replaced it with UL-61800-5-1, which changed the way short circuit testing of the VFDs is done and what it takes to pass. Under the old standard, the VFD did not have to consider the possibility of a line-to-load failure because the possibility was so extremely rare that under that old standard, UL felt it was not a significant risk. But the new standard has adopted the IEC testing requirements, which do require testing further possibility. That is why new drives are not required to have additional short circuit testing, generally resulting in the inclusion of high speed fusing. Drives that were previously listed under the old UL-508C can remain listed, but as they age out, their replacements will have to pass listing under the new standard. This standard was released back in 2012 and manufactures were given 10 years to affect the changes. That time was up in 2022 and now all drives released since then are going to have to conform.
The reason I bring this to everyone’s attention is twofold: understanding what is coming or has changed, and to point out that any drives still showing that they “don’t need anything” are at best, of a design over 10 years old and likely headed for obsolescence. So that should be taken into consideration when selecting a drive for a new installation.
Bottom line: any device in a circuit needs short circuit protection and per NEC rules, that must be in accordance with the manufacturer’s listing and instructions. But if a drive says it does not need fuses or is not specifically listed with a specific circuit breaker ahead of it, it is either not listed at all, or not long for this world.
read drive manual, not always true. If you do it tells you what type fuses are acceptable. They usually not RK5 either.
At same time should the front end rectifier of the drive fail, it is still toast, and for drives less than 10 maybe up to 25 hp they aren't worth repairing and you need to replace whole drive anyway. The type of fuse used may lessen how spectacular that failure is though.
As far as what was termed bad front end rectifiers failing in the over 500 drives we had I never had a 2 to 250 HP drive rectifier go bad. Ones that have five terminals, three for input and two for DC output. Started out with parajust drives back in the 1980's then Fin Corrs ( both out of business ) then Allen Bradley and finally Danfoss & ABB. Never had to change out any rectifiers. They all had an aluminum mounting plate that bolted to aluminum plate to dissipate heat. We had approximately 60 ABB 5:HP drives in a five story underground boarding garage for air circulation and at least 5 burnt out within two years and disappointed that the only replacement board was the touch screen that were used in majority of drives. Back in the 1980's the 2 & 3 HP Parajust drives had replacement boards and company would repair them. They used six little boards to generate the three phase output.
