# 600v fuse



## 99cents (Aug 20, 2012)

Depends on the class of fuse. If the class of fuse you're using is made in 250V, you have to change them out. If it's only available in 600V (like a J fuse), you're good to go.


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## neiljthornton (Jun 18, 2013)

That's great. Thanks


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## oliquir (Jan 13, 2011)

no problem, you could use a 600v fuse on 24vac system if you want!


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## 99cents (Aug 20, 2012)

oliquir said:


> no problem, you could use a 600v fuse on 24vac system if you want!


Wrong.


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## Jhellwig (Jun 18, 2014)

99cents said:


> Wrong.


Explain.


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## NC Plc (Mar 24, 2014)

I was under the impression that you could use fuses on circuits with less voltage than they are rated for to a point, but if you put the fuse in a circuit with too much of a lower voltage you can start to see issues depending on the type of fuse.

Like, a 600v on a 208v circuit is fine but a 600v on a 24 or 12v circuit is starting to get iffy because there is a lower limit on fuses it's just really, really low.

This is actually something I am interested in because I have applications in cabinets where some of the fuses are hard to find.


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## AK_sparky (Aug 13, 2013)

voltage drop across a fuse is going to be the same at a certain current flow regardless of supply voltage. In my mind it should matter if it is rated to a higher voltage.

I'm curious though if I assumed wrong.


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## 99cents (Aug 20, 2012)

As an example, "R" fuses come in 250V and 600V. A Bussmann FRN-R is 250V and an FRS-R is 600V. With Bussmann, "N" often means 250V and "S" 600V. You always choose the fuse closest to your voltage, obviously without exceeding the voltage rating of the fuse.


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## 99cents (Aug 20, 2012)

NC EET said:


> I was under the impression that you could use fuses on circuits with less voltage than they are rated for to a point, but if you put the fuse in a circuit with too much of a lower voltage you can start to see issues depending on the type of fuse.
> 
> Like, a 600v on a 208v circuit is fine but a 600v on a 24 or 12v circuit is starting to get iffy because there is a lower limit on fuses it's just really, really low.
> 
> This is actually something I am interested in because I have applications in cabinets where some of the fuses are hard to find.


A lot of things come into play - voltage, IR rating, time/current relationships. You need to look at the fuse curves.


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## neiljthornton (Jun 18, 2013)

Thanks to all that have answered.you have been very helpful.


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## Big John (May 23, 2010)

neiljthornton said:


> Hi guys. I have a 3 phase 600v disconnect,I want to use it for a 208v system,can I still use the 600v fuse.


Changing the voltage applied to the fuse only changes the amount of current the fuse can interrupt during a fault. As long as you do not exceed the AIR of the fuse at the rated voltage of the fuse, changing voltage does nothing else to affect operation. 

The time-current curves depend on current only and an amp at 250V is no different than an amp at 600 volts. 

But the fuse still needs to be sized appropriately for the application, and if you're just using some leftover fuses that came with the disconnect, I doubt that those are.


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## sparky970 (Mar 19, 2008)

99cents said:


> A lot of things come into play - voltage, IR rating, time/current relationships. You need to look at the fuse curves.


fuses will open on overcurrent, it this current different at other voltages?


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## 99cents (Aug 20, 2012)

Okay, now this one has me confused.  I spent ten years with Bussmann and we always said to use the fuse with the closest voltage rating. Now, if I read the fine print in the SPD, it says to use a 600V fuse on 208V. I sent a message to Applications Engineering to see what they say. I will let you know.


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## oliquir (Jan 13, 2011)

when a fuse is listed at 600v it is ok for 0 to 600vac applications . people choose 250v fuse on 240v application just because those fuses are a lot cheaper. 
http://www.littelfuse.com/technical-resources/faqs/fuse-ratings.aspx#1


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## AK_sparky (Aug 13, 2013)

oliquir said:


> when a fuse is listed at 600v it is ok for 0 to 600vac applications . people choose 250v fuse on 240v application just because those fuses are a lot cheaper.
> http://www.littelfuse.com/technical-resources/faqs/fuse-ratings.aspx#1


This was also my understanding.

The 600V fuse cost more because they are made with higher insulation rating and are able to handle the higher available fault currents seen in a 600V system (vs <250V) without exploding or melting.


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## Big John (May 23, 2010)

AK_sparky said:


> This was also my understanding.
> 
> The 600V fuse cost more because they are made with higher insulation rating and are able to handle the higher available fault currents seen in a 600V system (vs <250V) without exploding or melting.


 And you'll see this in the size difference between them. 250V class fuses are shorter than the 600V fuses of the same AIR for that reason.


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## 99cents (Aug 20, 2012)

Okay, I get the Pompous Ass of the Month Award. Here is the response from Bussmann:


_It can be more advantageous to size the fuse to 250V rather than 600V if you know you will not be applying more than 250V to the fuse - but it is not necessary. The advantages are a smaller size and likely a lower cost. You can use 600V rated fuses at or below their voltage rating without any performance impact.
_

Dammit, I made it to December without being wrong. There goes my year  .


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## Big John (May 23, 2010)

The only people who are never wrong are the ones who don't do anything.


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## rip (Jan 8, 2009)

no problem, you could use a 600v fuse:thumbsup:


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## Jhellwig (Jun 18, 2014)

99cents said:


> Okay, I get the Pompous Ass of the Month Award. Here is the response from Bussmann:
> 
> 
> _It can be more advantageous to size the fuse to 250V rather than 600V if you know you will not be applying more than 250V to the fuse - but it is not necessary. The advantages are a smaller size and likely a lower cost. You can use 600V rated fuses at or below their voltage rating without any performance impact.
> ...



It's ok. To make a mends you can write a 50 page essay on coordinating ocpd or put "I was wrong" in big bold letters in your signature.


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## 99cents (Aug 20, 2012)

Jhellwig said:


> It's ok. To make a mends you can write a 50 page essay on coordinating ocpd or put "I was wrong" in big bold letters in your signature.


I'll take the essay. These guys don't read anything past three sentences anyway  .


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