breaker size

Merry Christmas
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frizbeedog said:
210.20 (A)?

Sorry about the dots. Should I start using metric? :grin:
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Among other locations (i.e. NEC2005 450.3).

I am still on the 2005 code so I can understand dots.
 
coulter said:
General design philosophy acording to carl (recognized as no more valid than anyone else's). Some exceptions apply.

Basic premise: Something broke or the fuse wouldn't have blown.

OPC doesn't protect the device. The device is protected by design. If the device goes bad and draws too much current, what is there to protect? - remember, "the device goes bad".

carl
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I'll agree with your basic premise that something broke, it doesn't mean the motor is bad and that trips the breaker the mount holding the motor could fail and the motor bind causing an overload if the breaker is rated for the wire the motor may now fail if the breaker is rated for the motor it will not fail.
 
bikeindy said:
I'll agree with your basic premise that something broke, it doesn't mean the motor is bad and that trips the breaker the mount holding the motor could fail and the motor bind causing an overload if the breaker is rated for the wire the motor may now fail if the breaker is rated for the motor it will not fail.
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I'll agree with that - for industrial. The more expensive the motor, the more protection one hangs on the motor to save as much as possible.

I'm still looking for some small motor or residential examples - still can't think of any.

carl
 
brian john said:
General design philosophy acording to carl (recognized as no more valid than anyone else's). Some exceptions apply.[/qoute]

I mean how can you not like this guy, I want to meet Carl.
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As with all of us telling the truth - plenty of reasons. But thank you (I think:cool: )

carl
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Thanks for all the feedback. Let me draw some conclusions. CB's are not just for conductor protection. They often protect equipment and determine the actual circuit rating. So my next question, is it possible to have a pc of equipment that is fastened in place and have a noncontinuous load of say 28 amps on a 30 amp CB? Give me some help I am trying to think of one.
 
lmchenry said:
So my next question, is it possible to have a pc of equipment that is fastened in place and have a noncontinuous load of say 28 amps on a 30 amp CB? Give me some help I am trying to think of one.
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Uh...Water heater. See 422.11 (E) nec 2008 for an example, one among many.

Overcurrent protection will be as required in the specific articles listed in table 240.3

Your examples are too general to provide you with a definitive answer. You're going to have to dig into it some more to start to get a handle on it. There is no one fits all answer.
 
lmchenry said:
Thanks for all the feedback. Let me draw some conclusions. CB's are not just for conductor protection. They often protect equipment and determine the actual circuit rating. So my next question, is it possible to have a pc of equipment that is fastened in place and have a noncontinuous load of say 28 amps on a 30 amp CB? Give me some help I am trying to think of one.
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How about an electric range or "counter top cooking unit". Even if you're the Iron Chef and cooking all day long, the burners cycle on and off even on high.
 
coulter said:
Give me an example of a residential motor that could overload under normal operation, that the OCP would save - I'm sure there are cases, I just can't think of any.
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Garbage disposal?
 
lmchenry said:
as far as the range it is cord and plug connected and restricted by 210.23 a1
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No its not. That only aplies to circuits with TWO or more receptacles (read 210.23 carefully). And I said counter mounted cooknig unit -- this is the built in version of the top of a range. There would typically be a built in oven near it too, either sharing the circuit or on its own.

I think there is some precidence for a breaker protecting equipment too. See 422.11(E): Single Non?motor-Operated Appliance. If the branch circuit supplies a single non?motor-operated appliance, the rating of overcurrent protection shall:
(1) Not exceed that marked on the appliance.
(2) Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or
(3) Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.
 
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