VFD and GFI
VFD and GFI
(OP)
I've had a little bit of experience with VFDs - enough to know about the characteristic leakage current to the ground circuit. If fed a single phase input, is there anyway to get a GFI style protection?
To further state the issue: using VFDs in residential applications with either 115 or 230 volt single phase input driving a 3 phase motor for pump use. Since water is involved, I'm fairly certain that GFI are required per NFPA 70. But VFDs trip standard GFIs, so it seems a catch-22.
To further state the issue: using VFDs in residential applications with either 115 or 230 volt single phase input driving a 3 phase motor for pump use. Since water is involved, I'm fairly certain that GFI are required per NFPA 70. But VFDs trip standard GFIs, so it seems a catch-22.





RE: VFD and GFI
If you really want to have such protection, you need to used the equipment protective GFCI which essentially are less sensitive, trips at 30mA or more , compared to 4-6mA sensitivity for personnnel GFCIs required in bathrooms or kitchen.
RE: VFD and GFI
http://www.bender.org/lifeguardgfci.html
"Venditori de oleum-vipera non vigere excordis populi"
RE: VFD and GFI
The GFCIs are for a personal protection. VFD is not considered in areas of GFCI protectors or protection. Ground fault relays or monitors, which are different from GFCI, take over. Visit
http://www.startco.ca/se701m.pdf
etc. for ground-fault monitor
RE: VFD and GFI
Thanks for the links and info.
RE: VFD and GFI
RE: VFD and GFI
Some VFD's have earth protection built into the electronics anyways so this might give you the protection that you require. Trouble is that some shut the motor down but you still can have potential at the output.
Check the drive manual and contact the drive supplier if possible.
Rugged
RE: VFD and GFI
I suggest your VFD be integrated to the pond and pump; the receptacle that provides the input power has the GFCI. The cord shall be unplugged for servicing the pond. I assume the protection is for humans since the fishes are at the water potential.
RE: VFD and GFI
There's no way you could reliably do GF tripping upstream of the VFD, you'd get too much nuisance tripping, you'd never be able to discriminate VFD leakage current from fish-electrocuting current.
As ruggedscot has pointed out, you could buy a VFD with built-in GFI.
jbartos -- I'm scratching my head on the iso tx suggestion. How would that provide GF protection?
RE: VFD and GFI
Then I noticed the VFD manual specifically says to use an adjustable GFCI and set to 200mA and not less than 0.1 second. This might be a cheaper solution as the Bender LifeGuard GFCI units are pricy.
RE: VFD and GFI
A GFI with more than 30 mA tripping current will probably not save the life of the person thet gets zapped. The 200 mA recommendation is murder waiting to happen.
Have a look at this link for more information;
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html
RE: VFD and GFI
300mA GFI are for system protection, they are designed to protect an installation from ground faults, not for human life preservation.
Rugged
RE: VFD and GFI
The human body seldom/never lets as much as 300 mA through - it would require a very low resistance - so the 300 mA GFI never trips. The lethal current (somewhere between 30 and 300 mA) continues to flow and kills the poor person.
One could say that the tripping condition is not met. So, 300 mA GFIs are accidents waiting to happen. They are dangerous.
RE: VFD and GFI
Rugged
RE: VFD and GFI
RE: VFD and GFI
If there is any risk then that risk should be removed but this is not a perfect world so we need protection. 10mA GFI's can be fitted at outlet but really the sparkie working should be well versed with all types of GFI's.
Rugged
RE: VFD and GFI
RE: VFD and GFI
Sorry that fuse keeps blowing lets change it to a 6 inch nail....
that is the same logic. Clearly if it is changed to a 300mA GFI then the guy changing it doesnt know his job, or is being forced to do so by someone else, maybe he hates getting disturbed from his coffee and donuts.
There is no excuse for this one, better education is required. I had one a few years back guys fitting GFI 3 poles in as main breakers thinking that they were the main protction isolator. It was only when I hooked one up with a dead short on the output that they saw that it wasnt an overcurrent device. Blew the ass out of it but it probably helped educate them. Some people really need such things explained to them in a simple and constructive manner so that they dont go making ill informed decisions.
Rugged
RE: VFD and GFI
RE: VFD and GFI
However, I am under the impression that European GFI devices operate at a much higher level -- maybe 30mA? -- even for personnel protection. Can anyone confirm the IEC (or whatever is applicable) requirements for GFI in European installations?
RE: VFD and GFI
this isnt GFI'd as they think the leakage through 55 to ground would be 'safe'.
Rugged
RE: VFD and GFI
RE: VFD and GFI
RE: VFD and GFI
chip of the old block you see
Rugged