Need help with NEC wire sizing question

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Daniel malack

Daniel malack

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Location
Amissville, Virginia USA
Name plate also should give minimum over current protection. If you fuse it at 30 you will have a lot of service calls. For blown fuses. I always install the max breaker, and to save money minimum circuit amps!! Savvy

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Boiler Man

Member
Location
Springfield, VA, USA
Daniel, I'm not asking how to do it. Obviously you follow the nameplate. I was trying to figure out WHY it is done the way that it is so I could better understand.

Rob, thank you for the knowledge. I appreciate it.
 
infinity

infinity

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Staff member
Location
New Jersey
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Journeyman Electrician
Daniel malack said:
Name plate also should give minimum over current protection. If you fuse it at 30 you will have a lot of service calls. For blown fuses. I always install the max breaker, and to save money minimum circuit amps!! Savvy

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You missed the point the 30 amp fuse scenario was hypothetical. :)

I will add that there is no requirement to use the MaxOCPD it's merely a design choice. You could use the minimum if you so choose but at some point you might end up with nuisance tripping as you've mentioned.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Daniel malack said:
Name plate also should give minimum over current protection.
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It is implied in the minimum circuit ampacity rating.

FWIW, in motor circuits, the circuit breaker or fuses are often called the overcurrent protection device but in fact, it (or they) serve as short-circuit, ground-fault protection device(s).
 
infinity

infinity

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Location
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Boiler Man said:
Daniel, I'm not asking how to do it. Obviously you follow the nameplate. I was trying to figure out WHY it is done the way that it is so I could better understand.

Rob, thank you for the knowledge. I appreciate it.
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You're welcome. :cool:
Sorry if the 30 amp fuse thing was confusing I was just trying to illustrate how the overloads at the motor would protect the conductors.
 
Daniel malack

Daniel malack

Senior Member
Location
Amissville, Virginia USA
Sorry! Always go by name plate ratings. Years ago the electrician had to do the calculations. Now it is done for us. (Name plate) rating tells us everything we need to know. If it says max breaker 50 put in a 50. If it says minimum circuit amps at 30 install a #12 BECAUSE OF THE * NEXT TO #10 AMPACITY . If you want to install a #6 go ahead. Like I said it makes sense to me. SAVVY!

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infinity

infinity

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Location
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Daniel malack said:
Sorry! Always go by name plate ratings. Years ago the electrician had to do the calculations. Now it is done for us. (Name plate) rating tells us everything we need to know. If it says max breaker 50 put in a 50. If it says minimum circuit amps at 30 install a #12 BECAUSE OF THE * NEXT TO #10 AMPACITY . If you want to install a #6 go ahead. Like I said it makes sense to me. SAVVY!

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You cannot use #12 conductors for a MCA of 30 amps.
 
infinity

infinity

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Daniel malack said:
Explain the * Beside the # 14, 12, and 10 awg. Ampacity chart.

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That means that you do not have to follow the ampacities in 240.4(D) for #14, #12 and #10 conductors. #12 NM cable is only permitted at it's 60° C ampacity which is 20 amps. MC cable and conduit and wire is permitted at the 75° C ampacity which is 25 amps. You cannot use #12 at 30 amps.
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
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Consulting Electrical Engineer - Photovoltaic Systems
Daniel malack said:
Infinity s post was wrong, maybe I'm not familiar with how to post things. Just answering the last post I received.

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You didn't receive the post, the post was put up on a forum. When you reply without quoting we don't know what you are replying to, since other posts could have been put up between the one you are responding to and your response. Also, just saying "wrong!" isn't very informative.
 
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