Motor Fuse Type

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hoovermatt

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I'm connecting up a 10 HP 480 motor, direct drive on a blower so it has a high inertia start up. Because of the panel layout I wanted to use a disconnecting fuse holder. I used Class CC time delay 20 A 600 V fuses and they blow without even thinking about it. I'm wondering if a midget time delay is better a fit for what I need?

Thanks!
 
hoovermatt said:
I'm connecting up a 10 HP 480 motor, direct drive on a blower so it has a high inertia start up. Because of the panel layout I wanted to use a disconnecting fuse holder. I used Class CC time delay 20 A 600 V fuses and they blow without even thinking about it. I'm wondering if a midget time delay is better a fit for what I need?

Thanks!
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You can't use a midget fuse for a variety of reasons on a motor starter circuit. You MIGHT be able to use them if you are attempting to use the fuses as the sole method of protecting the motor (i.e. no OL relay), but if you do, then you cannot use those disconnecting fuse blocks. To use those on a motor circuit, the fuse holder must be UL98 listed, and if you use one that is, you will find that it is ONLY listed under UL98 if used with a Class CC fuse.

With a typical CC fuse, and assuming 14A FLC, you cannot use a 20A fuse unless it will accelerate in 2 seconds or less. The best you can do is a 30A fuse, which will allow you 8 seconds to accelerate. Any longer than that and you would be out of the type of fuse where you can use those little DIN rail disconnecting fuse holders, if that's what you meant.
 
Is there a good reason to use class CC fuses?

20 amp RK5 fuse works great for a 10 HP motor in most cases unless you would have really high available fault current - over 100kA but as short circuit and ground fault protection you do need additional overload protetion.

I have seen many many 15 amp RK5 on 10 HP that hold during starting - maybe could a little more of a problem if you have a high inertia load though.
 
kwired said:
Is there a good reason to use class CC fuses?

20 amp RK5 fuse works great for a 10 HP motor in most cases unless you would have really high available fault current - over 100kA but as short circuit and ground fault protection you do need additional overload protetion.

I have seen many many 15 amp RK5 on 10 HP that hold during starting - maybe could a little more of a problem if you have a high inertia load though.
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I had assumed it was because he wanted to use this type of disconnecting fuse holders. If 10HP would be only a 20A fuse, it would mean 600V RK5 or RK1 fuses, which would be 3x the size in the panel.
4682818.jpg
 
Jraef said:
I had assumed it was because he wanted to use this type of disconnecting fuse holders. If 10HP would be only a 20A fuse, it would mean 600V RK5 or RK1 fuses, which would be 3x the size in the panel.
View attachment 12040
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Size matters:lol:

But if fuse type used won't allow starting it still doesn't do you much good. Throw in a soft starter and you used up space that could have been used by physically larger fuse type, though maybe not quite the space RK5 fuseholders would take up.
 
Jraef said:
I had assumed it was because he wanted to use this type of disconnecting fuse holders. If 10HP would be only a 20A fuse, it would mean 600V RK5 or RK1 fuses, which would be 3x the size in the panel.
View attachment 12040
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Are those permmited to be used as a motor/motor controller disconnecting means when multipoles are needed?
 
kwired said:
Are those permmited to be used as a motor/motor controller disconnecting means when multipoles are needed?
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Some are, but those that are (UL98 as a "disconnect switch" with a HP rating) can only achieve that rating if the fuses are Class CC, not midget. It's a careful little dance, I've been burned listening to salesmen who didn't understand the subtleties. UL inspectors are savvy to it though.

For example Bussman has some that are, some that are not. Those that are will be more money than those that are not, as you might imagine. That image above I grabbed really quick from Littlefuse actually is probably not, I was just going for the style.

http://www.cooperindustries.com/con...cal-literature/BUS_Ele_App_Notes_3139_CCP.pdf
 
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