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#187496 - 06/28/09 11:29 PM Which Cartridge Fuse?  
thiggy  Offline
Joined: May 2004
Posts: 24
B'ham Al
I have an old family farm house with a 125 amp Square D breaker box. The service disconnect is a 100 amp Square D cartridge fuse. I have never had the main blow, but I decided that I better have a spare pair of fuses on hand just in case, as in this rural area it would be difficult to locate one in a hurry. I drove to the nearest city and located fuses at Lowes, but I am not sure which one of the two types they had should be used for my application. The heavy-duty time-delay one said it is "for motor and main panel protection. (FRN-R)" It indicated that "for lighting or electric heating circuits use general purpose fuses.(NON)" I use window AC units for cooling, and 1500 watt portable heaters for infrequent use in winter heating. Water heaters are also electric. (This is generally just a week-end house.) Which type of fuse would be the most appropriate for my use?

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#187497 - 06/29/09 01:41 AM Re: Which Cartridge Fuse? [Re: thiggy]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,116
I would go with the FRN.
That will tolerate a short time spike in current.
The biggest opportunity for a spike in current is when you have a power glitch and the service would see locked rotor from every motor that was running at that time.

Greg Fretwell

#187499 - 06/29/09 04:28 AM Re: Which Cartridge Fuse? [Re: gfretwell]  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,222
SI,New Zealand
I agree with Greg.
You really need something with a bit of time delay on it for a main fuse.
After all, the fuse/CB that is electrically closest to the fault (ie, a sub-circuit fuse/CB) should operate first, in any electrical system.
Anything less is poor design.

Let's face it, these days if you're not young, you're old - Red Green grin

#187503 - 06/29/09 12:19 PM Re: Which Cartridge Fuse? [Re: Trumpy]  
electure  Offline

Joined: Dec 2000
Posts: 4,261
Fullerton, CA USA
You answered your own question.

The heavy-duty time-delay one said it is "for motor and main panel protection. (FRN-R)"

#187509 - 06/29/09 01:09 PM Re: Which Cartridge Fuse? [Re: Trumpy]  
thiggy  Offline
Joined: May 2004
Posts: 24
B'ham Al
Thanks for the responses. I shall go with the time delay fuse. (I actually bought two of both types with the intention of returning one pair after I determined which type I should use.)

#187517 - 06/29/09 08:24 PM Re: Which Cartridge Fuse? [Re: thiggy]  
JBD  Offline
Joined: Jul 2001
Posts: 599
There is almost no reason to ever install an NON fuse. For all intents NONs are old technology, and are almost always sold based on price only.

#187526 - 06/29/09 11:36 PM Re: Which Cartridge Fuse? [Re: JBD]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,116
We used NONs to protect electronics and there was even a faster blowing fuse that we used for the input to switcher power supplies way back when they were a big cabinet full very expensive parts.

Greg Fretwell

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