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Joined: Jul 2002
Posts: 8,450 Likes: 4
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Just wondering, is there a standard progression in the sizes of fuses/CB's in the US.
How would you protect each size/type of cable available to you?.
Would this vary between a Domestic or Commer-
cial or Industrial Installation?.
How are fuses that protect Motors, sized?.
Your help would be most appreciated.
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Joined: Mar 2001
Posts: 2,056
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The NEC lists standard fuse & circuit breaker sizes (Article 240.6).
I'm sure someone here can download the article.
Generally, fuses that protect motors can be sized up to 300% for Nontime-delay and 175% for Time-delay. (Table 430.52)
There are exceptions to these rules.
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Joined: Jul 2002
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Thanks, Redsy. ![[Linked Image]](https://www.electrical-contractor.net/ubb/smile.gif)
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Joined: Aug 2001
Posts: 7,520
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240.6 Standard Ampere Ratings
(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted. I seem to recall a thread a few months ago discussing the reason for the peculiar 601A rating, although I can't remember the explanation. [This message has been edited by pauluk (edited 02-05-2003).]
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Joined: Apr 2002
Posts: 7,413 Likes: 10
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Trumpy:
I see Paul UK beat me to posting the table.
Residential is mostly circuit breakers nowadays. You may see fuses at the central AC condenser IF the mfg spec's FUSES, if not it's a HACR rated CB. There are still some edison (plug) fuses in old homes, and some cartridge fuse main service discos around.
Commercial and industrial lighting and GP circuits are also CB's. Fuses for motors and equipment. Fuses are a preferred OCP where a high AIC rating is required, as the high AIC rated CB's are very pricey.
OCP (overcurrent protection) for cables is based on the NEC; Tables 310-16 to 310-86 of the '99 NEC. If you would like a copy of the tables, e-mail me your address, and I will mail you them.
Hope the above helps
John
John
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Joined: Jul 2002
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Paul, Thanks for posting them fuse sizes, I never really thought that so many sizes of fuses, were available. I also realise that CB's make up this list too. Hotline, Thanks for the back-up info, too, most appreciated!.
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Posts: 362
Joined: April 2003
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