Vector Drive Fuse Selection

I think this calls for a 30A circuit with #10 wire, would go with THHN....You may have misread the manual....

The fuse is just for the case the drive internal circuitry fails. Until then, motor current, (including overcurrents and shorts) is checked and controlled at a rate of few thousand times per second from inside the box you just bought. Fuse is oversized at 60A for single phase input and 40A for 3 phase input (your drive can take both), to handle the input side inrush current at plugging-in and at brown-outs. There is nothing to worry about, except for the higher cabling cost. But you still have to program VFD parameters correctly for your application and motor. S.M.

It is my understanding that you can program in a soft start, limiting motor start inrush current...

Of course you can make starting as soft as you want, I'm talking about the inrush current of charging the "empty" DC rail bulk capacitors inside the drive, when we first connect to mains, and it's a quite high current value (not very predictable since connection happens at a random point of AC cycle) but fortunately has very short duration. Usually VFDs incorporate circuitry (NTC etc) to limit it to a safe level but... S.M.

Hi and thanks for the quick replies,

I have read that there are LARGE caps in these drives and therefore the need for a higher amperage fuse to allow for inrush current to the drive. The problem I see is going to be the main circuit breaker for the control cabinet. The cabinet is going to have the vector drive, computer, servo drives and possibly a small plc. I made a rough guesstimate as to the current draw for the added devices will be about 20 amps. So was thinking about a 50 amp main breaker, which I think with a fused 60 amp inrush current for the drive and the additional 20 amp load from control components will trip the breaker in a heartbeat. So do I up the main breaker to 80 or 90 amps which I feel is way to high or go with a 60 amp main breaker and install contactors, one to power up the vector drive first then the second one to bring in the rest of the electronics control after a time delay, which will add to the cost of the control cabinet. I haven't purchased the control cabinet as of yet, and trying to figure out it's size so I'm trying to figure out how much room for what I'm putting into it.. Don't want to buy a mouse cage and during the assembly find that I have a bear going into the cage and not a mouse... LOL

Thanks Again

Since this is a single phase input, the input current is estimated at 22A at full load. If this is your application, then you need to cable for this current and then fuse to protect the cable. Strictly speaking, the fuse should be fast blow but hardly anyone uses these normally.

The inrush circuit (it looks like an LS / LG drive?) will limit charging current so this shouldn't be a consideration. Why not just switch on a a 20A breaker and see if it holds OK? Incidentally, the fuse / CB is to protect the cable not the drive, so your selection is this way around.

The input current will also depend on your load so if this isn't up to rating, neither will your input current be. If you want lower currents still, add an input AC reactor or DC link reactor (if possible).

The standard you refer to is not really relevant, most domestic supplies have high impedance so this will also reduce the current in practice (also may distort the voltage a little).

Should be no problem I'd have thought, normally. Let us know how you get on.

Assuming here that you are in the US.

The NEC requires that the conductors be sized for a MINIMUM of 125% of the rated input current of the drive (430.22 I think), so that puts you at 27.5A, hence the 10ga minimum wire size mentioned earlier. 10ga wire must be protected by a MAXIMUM 30A OCPD, Over Current Protective Device, ie fuse or breaker. You can go larger though should you want to. If you go with a 40A OCPD, that cannot legally protect 10ga wire, you will have to run 8ga wire to the drive input,. So you must then make sure the terminals of the drive can accept that size conductor.

This by the way would be totally separate from your Main breaker for a control panel, this must be the BRANCH protective device, because despite the VFD it is still a motor controller circuit.

Realize that DuraPulse, although sold by AutomationDestruct in the US, is a Korean drive so the manuals are translated from Korean for the Korean market. We have different rules here. You have to follow our rules as laid out in the NEC. Forget the "inrush" issue on VFDs, it is only for charging the caps and on a small drive like that, lasts for only a few cycles, way too fast for a fuse or breaker to clear. The drive also will have an internal current limiting resistor on the DC bus to keep the charging current low. The only reason they say 40A is because they have to list a MAXIMUM size at which the VFD will not actually catch on fire. They are too cheap and lazy to go into details that may vary from country to country, so they only show what is minimally necessary.