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fireryan

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Is it permisible to put 8awg on a 50 amp bkr. I know in the code it says #12 on a 20 amp bkr and # 14 on a 15amp bkr. Is there anything on #6 and #8's. It seems you always put a 8 on a 40amp bkr even though it is good for 55amps when using thhn.
 
Is 240.4(D) the information your looking for? It's verbage on Small Conductors. The verbage only takes in up to #10.
 
Couple of things...

fireryan said:
Is it permisible to put 8awg on a 50 amp bkr.
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If it's NM ~ no.
It would limited to 40A [60? col.]
See 334.80


fireryan said:
It seems you always put a 8 on a 40amp bkr even though it is good for 55amps when using thhn.
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Not really...a #8 CU THHN is actually only good for 50A [75? col.]
See 110.14(C)
 
fireryan said:
It seems you always put a 8 on a 40amp bkr even though it is good for 55amps when using thhn.
Click to expand...

You build according to the weakest link in your circuit/feeder. . You have 3 links.
1] conductor insulation rating
2] termination [lugs] temp
3] cable rating

Celtic already covered an example of a cable [NM] rating that would drop you to 40A [T310.16 : 60? column]

celtic said:
If it's NM ~ no.
It would limited to 40A [60? col.]
See 334.80
Click to expand...

Sure your THHN conductor insulation is good for T310.16 : 90? column

But good luck on finding breaker lugs rated at 90?. . The normal 75? lugs are only good for 50a for 8gauge.

PS
Even if you get a breaker with 90? lugs, the lugs on the load equipment would also have to be rated at 90? or you're still stuck at 50a.
 
Also if you're using SE cable under the 2005 you can use the 75 degree rating. Under the 2008 you're limited to the 60 degree rating.
 
Agreed but just wondering where the 60A came from. If the FLA of an A/C unit was 50A, we could use an OCPD of 90A and still use #8THHN's........correct?
 
A/A Fuel GTX said:
Agreed but just wondering where the 60A came from. If the FLA of an A/C unit was 50A, we could use an OCPD of 90A and still use #8THHN's........correct?
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I was just trying to make the point that the OCP does not necessarily have to match the wire sizes as given in 310.16. I didn't do any calculations. The motor load could be 45 amps or 40 amps etc.
 
I see. I generally run conductors sized to the minimum circuit ampacity and the OCPD to the maximum fuse size.....
 
A/A Fuel GTX said:
... and the OCPD to the maximum fuse size.....
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CAREFUL here ... fuses and circuit breakers are different. If it says fuses, it means, usually, FUSES. If it matters there will probalby be a specification on the fuses.
 
GeorgeB said:
CAREFUL here ... fuses and circuit breakers are different. If it says fuses, it means, usually, FUSES. If it matters there will probalby be a specification on the fuses.
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I have not seen an a/c unit that says fuses only in many many years. Of course I don't do commercial work so I am talking resi stuff here.
 
Dennis Alwon said:
I have not seen an a/c unit that says fuses only in many many years. Of course I don't do commercial work so I am talking resi stuff here.
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I check AC nameplates on every single final inspection [and service/breaker panel replacement] both rez and commercial. . I have only seen the max breaker and max fuse listed as different values one time in almost 4 years. . I've also noticed that listing separate maxs is becoming less common. . I see alot of "max OCPD" wording.
 
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