Wire Sizes

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Alwayslearningelec

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What problems would this pose.

1P-20A breaker feeding (1) LED lights. Using a larger wire size than say #12 or #10 wouldn't pose a problem( say #8) would it?

I know you would really never just do this. I'm trying to grasp the concept of using larger wire size( higher current carrying capacity) than the breaker.
 
This probably isn’t the intent of the question.... but a somewhat related question I have to the people in the field. Generally, between manufacturers what’s the biggest wire you can connect to a 20/1 breaker? I looked one up quickly, is #8 accurate ? I feel like I’ve upsized to #6s sometimes due to voltage drop before, I don’t check maximum sizes for smaller breakers alot, maybe I should pay more attention ....
 
Charged said:
This probably isn’t the intent of the question.... but a somewhat related question I have to the people in the field. Generally, between manufacturers what’s the biggest wire you can connect to a 20/1 breaker? I looked one up quickly, is #8 accurate ? I feel like I’ve upsized to #6s sometimes due to voltage drop before, I don’t check maximum sizes for smaller breakers alot, maybe I should pay more attention ....
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If the breaker is only listed for #8 and you want #2 you can splice the #8 to the number #2 in the panel just before you terminate in the breaker.
 
It wouldn't pose any electrical problem. In fact, the larger the wire, the better as far as the electrons are concerned. It might be a logistical problem if the larger wire has to fit in a conduit or a small box. As Buck said above, you can always splice on a smaller wire to terminate in the breaker. You can run it with 500mcm is you want.
 
Voltage drop, more than 3 current carrying conductors in a raceway, de-rating for elevated ambient tempratures, ground fault loop impedance in long runs, among others, are just a few reasons why a conductor may be larger than the OCPD.
 
Buck Parrish said:
If the breaker is only listed for #8 and you want #2 you can splice the #8 to the number #2 in the panel just before you terminate in the breaker.
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Thanks for reply. Is everything code legal with that? I know there is a note in chapter 9, for table 1 that lets you increase fill/decrease conduit size for the last 24” . (That reference may be wrong , no book in front of me) Is there something similar for wire ?
 
Can you do that with service conductors too? For example if the service conductors were larger than code minimum for whatever reason, maybe #600cu for 400A. Could you splice down to 500s if the 600s were too large ?
 
While true that upsizing conductors generally causes no issues and sometimes is desirable or necessary. But there also can be downsides, especially in larger circuits as larger conductors can elevate the available fault current that may have to be addressed.
 
texie said:
While true that upsizing conductors generally causes no issues and sometimes is desirable or necessary. But there also can be downsides, especially in larger circuits as larger conductors can elevate the available fault current that may have to be addressed.
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Never considered that. Most times we're trying to get the most out of the wiring ie voltage drop reduction, but I can see if AFC (Available Fault Current) is already marginal that voltage drop can be your friend for AFC. Have seen that one way to get the numbers within equipment specifications for AFC was to add extra wire length vs changing equipment with one that has higher kaic ratings, just didn't think of reason this works was effectively VD, but yes, both effected by conductor resistance. Thanks.
 
Not going to mention the cost...

Oops, I mentioned it. If you already have the #8 run for some older circuit, not an issue, in fact changing to #12 would cost you. But buying #8 when you could have used 12 or 10, in today’s bizarro world marketplace, will cost you a pretty penny.
 
For that single LED lamp even 14 AWG might be overkill for the needs of the lamp, but NEC kind of limits us to 14 AWG minimum for general use branch circuits.

Yes many miniature circuit breakers 30 amp and less only accept 8 AWG max, as mentioned you can reduce the conductor size someplace near the breaker if needed.

Some industrial breakers (30 amp or less) might accept larger conductors, still probably maxing out around maybe 2 AWG I'd guess.
 
tom baker said:
I have heard of eddy current, but dont understand. Can you explain?
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To much metal volume can create electric swirls in the conductor carrying the small load. Assuming the OP is using #8 stranded it likely not be an issue. As a divide or change in the current carrying metal will help to prevent the swirls. But if the OP was using a bus bar for the same load, he would likely get Eddy Currents.
The way I remembered it was simple. To big of a conductor used may cause swirls (a closed loop) called Eddy currents. That's my terminology as a field electrician. See here from an engineers perspective.
What are Eddy Currents? (magcraft.com)
 
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