Is tipping the breaker bad for a vfd?

A bit of clarification, VFD's have a large capacitive reserve and also use the regenerative energy from the motor to effectively brake the motor to a stop if programmed to do so. If you shut off the power to a VFD, they may stay on for a minute or two with no load. But there are other factors such as a dropout power relay or contactor that prevents restart. People that direct wire the controls via 2 wire control, the VFD can restart in some situations. So most VFD's should not be effected if the power is killed under operation, just wouldn't want it to be a frequent occurrence.

The other issue is VFD's are not designed to be switched on/off frequently, and most VFD manufactures recommend at least 5 minutes before repowering the VFD. This allows the capacitors to discharge. Frequent on/off powering will lead to earlier capacitor failure and also the inrush protection circuit will fail prematurely. Using an E-Stop to break power to the VFD is not often recommended in an emergency, you loose braking ability, these days the more common method is an interlock system that disconnects the output section, but it varies depending on the function of the E-Stop and if their is an alternate emergency mechanical braking system that will instantly stop the system.

A 30A circuit for a 5Hp motor, is not adequate, although the running unloaded amperage is probably below a 30A input, at load it can/will be higher depending on the load. Circuits in houses are not designed to handle 100% load, it is more like 80% continuous. So you are pushing risk of the wire over heating and fire. The other factor that is often overlooked is that input wiring to the VFD is based on the VFD rating and not it's load rating or what it is driving. In this case you will need a 7.5-10Hp 3 phase input VFD derated for single phase (or an oversized generic Chinese VFD say 7.5HP), you are looking at some very high potential input current load. I am dealing with several installs with 5HP motors using 3 phase VFDs with the WJ-200-075LF, the input single phase current is around 70A and sometimes they recommend a breaker at 125% of the VFD input load. In this case we are going to try to run it on a 50A breaker service with #8 wire on the input, we are running a high efficiency 3 phase 5Hp motor. We will also add 50A fusing at the VFD cabinet.
 
Thanks for the help. As you can tell I know nothing about VFDs. I was guessing that 30 Amps would do 5 horse since 15 will do 2 at 110. According to my wet vac it will do 6, but I know that is marketing but I figure 2 for a real motor. I I didn't know I would need to oversize the VFD, that is annoying.

I'm starting to think that I should just remove the motor and install line shaft. I've got plenty of power in my tractor collection.

I know the compressor needs to be fixed. I've looked at it a few times but haven't really dug into it. Too many projects and I'm not how much effort a 15 year old oilless is worth.
 
Back
Top