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#187496 06/28/09 11:29 PM
Joined: May 2004
Posts: 24
T
thiggy Offline OP
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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?

Joined: Jul 2004
Posts: 9,687
Likes: 10
G
Member
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
Joined: Jul 2002
Posts: 8,412
Likes: 3
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Yeah,
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.

Joined: Dec 2000
Posts: 4,289
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You answered your own question.

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

Joined: May 2004
Posts: 24
T
thiggy Offline OP
Member
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.)

Joined: Jul 2001
Posts: 599
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JBD Offline
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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.

Joined: Jul 2004
Posts: 9,687
Likes: 10
G
Member
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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