Fuse switch rating for vsd

[Indy]

Hi,
Following on from my question about reusing a fuse switch to supply a control panel containing a vsd. The rating of the drive is 18.5kw. We will need to use a motor rated fuse. We are planning on using a 10mm cable from the switch to the control panel. My query is would a gM32m 40A motor rated fuse be too small. I believe it seems small, but a gM63M 80 seems big,has anyone else came across this before?

Thanks

 

[waross]

You are not feeding a motor, you are feeding a VFD.
The starting current of a VFD is not the same as the starting current of a DOL motor.
Different rules in some jurisdictions.
It is generally safe to fuse a VFD at 1.25% of the rated input current of the VFD.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

99% of the time, the VFD mfr has provided you with their recommended fuse size AND TYPE in their installation manual. I highly recommend following that recommendation and in some jurisdictions it is a legal requirement anyway.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Indy]

Thanks for this. All we have at this stage is a motor rating of approximately 35A and this will be fed from the VSD. The vsd and motor system will be fed from a fuse switch. At this stage would it be safe to assume a 50A fuse rating for the fuse switch.

Thanks

 

[waross]

Forget the motor.
What is the input rating of the VFD?
That is what you must base your requirements on.
You are connecting a VSD.
The rules may be different. The rules are definitely different in North America.
The fuse and supply cable is based on the VFD specs, not the motor specs.
If this is a soft start, say so.
A soft start is NOT a Variable Speed Drive.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Indy]

Hi, all we have at this stage is that it will be an 18.5kw motor controlled by a vsd. We have an existing fuse switch that we are planning on reusing. At this stage we are estimating the rating of the vsd and the protection that is required for the drive system.
Thanks

 

[jraef]

So do you not have an installation / operation manual for your VFD? Post the name and model, my Google-Fu is strong today...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[ScottyUK]

A standard BS 88-2 distribution-class fuse will be fine. If the drive gets in enough trouble to blow a semiconductor fuse then it's already toast. You're protecting the installation wiring, not the load.

Motor-rated fuses in the Uk come in two flavours: one which has defined breaking capability over only part of the current range which must be used with a thermal overload relay ('aM' class), and the other type which are an over-sized fuse element in an smaller body size, intended for short-circuit protection. The latter are usually denoted by (e.g.) 32M20 which denotes a 32A fuse element in a 20A body size which is OK for backup protection to a combination starter but totally unacceptable as a distribution fuse. You don't need either of these for a VFD supply.

 

[GroovyGuy]

Hi there Indy,
What is the NP voltage & current rating of the VFD?

GG

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)