# 60 hp motor



## alcelectrician (Mar 29, 2012)

i have a 60 hp 480v motor for an ingersol rand air compressor that has a vfd controlling it. the service rep said to use fast acting fuses for the disconnect. if i go by the code it says for fast acting fuses, multiply the fla by 300% which would be (table 430.52)

77amps x 300%= 231 amps

now, i would think that i would be better off using 200amp fuses since the next size would be 300 and that goes well over my 231 amps. does this seem right to you guys, am i missing something?

and also, would i still have to use a 200amp circuit breaker that would be for my motor branch ciruit that is upstream from the disco? ulgys book page 41

thanks


----------



## ponyboy (Nov 18, 2012)

You can go over 300% but you shouldn't have to. I'd question why he doesn't request dual element fuses. If its got a VFD I'm sure it'll be on a ramp start


----------



## ponyboy (Nov 18, 2012)

another point is i dont let service reps tell me how to do my installs. i will follow all their specs to the letter but there's always these company techs that want things the way they want them but unless its part of the warranty paperwork or in the specs its getting done my way. just a thought


----------



## wildleg (Apr 12, 2009)

what type of fuses are you using ? a lot of fuse styles come 225, 250


----------



## JRaef (Mar 23, 2009)

ponyboy said:


> another point is i dont let service reps tell me how to do my installs. i will follow all their specs to the letter but there's always these company techs that want things the way they want them but unless its part of the warranty paperwork or in the specs its getting done my way. just a thought


Actually to that point, it really doesn't matter AT ALL what he tells you verbally, you have to install what the VFD manual tells you that the VFD requires ahead of it, that is part of their UL listing process. If you do NOT do what their manual says, you are accepting full responsibility for the drive. His verbal commands will evaporate at the first sign of trouble.

If their manual makes no mention of the OCPD requirements, then it is not likely UL listed, which brings up a whole different kettle of fish.

What's the mfr and model of the drive?

PS: That "high speed fuse" thing is kind of an old wives tale based on the mistaken belief that so called "high speed" semiconductor fuses will prevent damage to the power devices in the VFD. Not true, in spite of what the fuse mfrs want you to believe. I have NEVER seen a fuse clear on a drive and have the drive not be damaged. Never, in 30+ years of dealing with VFDs. the only thing they do is suck down a LOT more money after the failure because thy are the most expensive fuses out there..


----------



## Cow (Jan 16, 2008)

I go drive input FLA x 125% and round up to the next size. That's what size dual element fuses the drive will get. There are a million drives installed this way, his drive isn't magically different than any other....

Now if he wants to tell the customer they need a 400 amp fused disconnect with 250A fuses for a 60HP motor, then that's his deal. But I'm not going to make that recommendation.


----------



## alcelectrician (Mar 29, 2012)

im using H type fast acting fuses. and i also find it to be wierd that the ingersol rand tech wanted fast acting fuses, he was persistent about it. i dont have the model number yet, they are delivering it on tuesday. if i was to do the 250 amp fuses, should i just size the upstream breaker with the 125%, or does it need to be not less than that of the disconnect?


----------



## Jlarson (Jun 28, 2009)

Tell the compressor tech to go change oil and filters somewhere. 



JRaef said:


> If their manual makes no mention of the OCPD requirements, then it is not likely UL listed, which brings up a whole different kettle of fish.


Exactly, get the manual, find out real details.


----------

