Wire size to breaker size

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magicman76

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I have a tendency to size the conductors to the size of the breakers. Is there anywhere in the NEC that makes me do it this way or can I size the wire to the load of the circuit and then go up the next breaker size. I do this for street lighting and cameras along the highways. The reason I tend to size to the breaker size is for future expansion. Thanks in advance guys
 
Start with a review of Section 240.4 of the NEC and move on from there to the specific circuit type section (feeder, branch circuit, etc.) and/or equipment type for specific requirements.
 
magicman76 said:
I have a tendency to size the conductors to the size of the breakers. Is there anywhere in the NEC that makes me do it this way or can I size the wire to the load of the circuit and then go up the next breaker size. I do this for street lighting and cameras along the highways. The reason I tend to size to the breaker size is for future expansion. Thanks in advance guys
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You have me fascinated as usually the conductors used for these applications are very large compared to the actual load on them due to voltage drop considerations.

We might use 3 AWG copper to feed circuit of site lighting due to voltage drop but the actual load may be 15 to 25 amps.

We would never use a 100 amp breaker to supply it based on the use of the 3 AWG.
 
Like Iwire, I've also used rather large conductors for powering site & parking lot lights due to voltage drop. Largest I've put on a 20-a circuit is #0.

You may also violate the listing of the load if you upsize the breaker.

If an item has a nameplate that says "Max OCD 20amps" and you run 10s or 8s to it for voltage drop purposes, you still only use a 20a breaker maximum.

For example, the lighting in this auditorium was all run in #8, but they're all 20a circuits.

DSC03537a.jpg
 
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I guess what my question really is do you size your conductors to the breaker size or the load? I understand that you might have a bigger AWG then what your breaker is capable of handling due to voltage drop but can it be done the other way around.
 
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magicman76 said:
I guess what my question really is do you size your conductors to the breaker size or the load? I understand that you might have a bigger AWG then what your breaker is capable of handling due to voltage drop but can it be done the other way.
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Are you asking if it's OK to install a larger breaker just because you have larger wires installed for voltage drop?
 
480sparky said:
210.20 has your answer.

I'm still not clear on your original quesion, though.
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Thanks, I guess my question is can I run a #10 AWG (35A) to a 50 amp breaker or would it have to be a #8 (50A). In other words lets say there is an existing 50 amp breaker and my load is 28 amps can I size my wire to the load or to the breaker size?
 
magicman76 said:
Thanks, I guess my question is can I run a #10 AWG (35A) to a 50 amp breaker or would it have to be a #8 (50A). In other words lets say there is an existing 50 amp breaker and my load is 30 amps can I size my wire to the load or to the breaker size?
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Your wire size would be based on the load, then the breaker would be sized to both the load and the wire size.
With a few exceptions, #10 is limited to a 30a OCD. 240.4(D).
 
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