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Discuss Fuse switch sizing for a vsd in the Industrial Electrician Talk area at ElectriciansForums.net

Lc1

Regular EF Member
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, has anyone else came across this before?

Thanks
 

Spoon

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Don't they usually tell you what size fuse to use in the manual?
 

Lc1

Regular EF Member
I believe so but we are at an early stage and someone else will be buying the equipment. We are just finding a supply and saying preliminary sizing based on an 18.5kw vsd.
 

westward10

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Off the top of my head 40A is probably too small.
 

Lc1

Regular EF Member
Ok thanks, the next one I have found is a gM63M rating 80 Amps. Not sure if this will be oversized ?

Thanks
 

Murdoch

Electrician's Arms
Isn’t the cable size slightly more important at this stage?
 

Lc1

Regular EF Member
Yes we have sized that at approximately 10mm. And we have identified that the existing fuse switch type CM-UT 100A-415v can be reused, Wewould like to provide an estimated protection size, motor rated fuse gM so we have something to work with.

Thanks
 

Spoon

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... but we are at an early stage and someone else will be buying the equipment
Not being funny mate, but its hard to design something when you don't have all the info.
Best you can do is suggest a fuse size and state what vsd model you used to get the info.
 

Lc1

Regular EF Member
That’s my issue it’s just generic at this stage. So I can say motor rated fuse gM63 80A. This seems overized to me though but can’t find a smaller one
 

westward10

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40A may well be okay but may not. As others have stated you need hard spec from the vsd.
 

davesparks

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Yes we have sized that at approximately 10mm. And we have identified that the existing fuse switch type CM-UT 100A-415v can be reused, Wewould like to provide an estimated protection size, motor rated fuse gM so we have something to work with.

Thanks
Surely you need to know the rating of the fuse before you calculate the cable size, not after?
 

snowhead

Respected Member
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Trainee Access
A motor rated fuse is the last thing you want protecting a VSD.
The VSD protects the motor, the fuses in the supply protect the VSD which is an electronic device.
You need fast acting fuses as determined by the VSD manufacturer.
I've just retired and thrown all my VSD manuals out but here's a link to an ABB VSD and the fusing required.
Note, for a 18kw (25hp) they quote JJS50 fuse.
PDF page 32 actual page 22
https://library.e.abb.com/public/cb07980e2fd375bc8525733f004422cc/3AUA489002B5311_ACH400_00_UM_REVE.pdf
 

MDJ

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Single phase or three phase? Have I missed the answer somewhere?
 

Rocboni

Regular EF Member
ideally Semiconductor fuses req for VSD drives. Is this not taken care of in the control panel?
 

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