- Location
- New Jersey
- Occupation
- Journeyman Electrician
1) is correct
2) is correct
3) #8=50 amps there is no next size up so #8 is the answer.
what is the answer to these questions?
- Thread starter solar man
- Start date
2) is correct
3) #8=50 amps there is no next size up so #8 is the answer.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Right answers but logic on #2 and #3 is a bit off.
Since 40A is the 75C ampacity of 8awg and 40A is also a standard breaker you don't get to use the next size up no matter what that size might be. Similarly for the #10, with the additional detail that 240.4(B) generally does not allow the next size up rule for 10awg and smaller.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I think thst you meant #8 @ 75° C has an ampacity of 50 amps not 40.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I think you meant 240.4(D)?
There's no special interaction between 240.4(B) and 240.4(D), since the standard ampacities of #10, #12, and #14, at both 60C and 75C, are standard breaker sizes. And 240.4(B) can certainly be used when there is significant derating. E.g. (10) 14/2 NM cable crammed together in a hole through a framing member which is insulated. Very likely that's 20 CCC, so 0.5 ampacity adjustment, so an ampacity of 12.5A. Still fine to protect at 15A if they are supplying circuits other than multiple receptacles and with a calculated load of 12.5A or less.
But if any of the test questions were asking about 15A-30A breakers, then 240.4(D) would be something you need to follow.
Cheers, Wayne
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
That was regarding question #2 in the OP which said to use 60C
Yes. Sorry, that was a confusing typo.
Yes agree, but my point was we can simply state that if you're thinking of using 10awg copper (and not 240.4(G) and taps don't apply) on a 40A breaker you just stop, because you can't.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
@solar man The next size up rule is used only when the load is not over the conductor ampacity. Since none of the questions gives a calculated load then I would go straight from the table.
Eample of next size up. Say you use a #6 NM cable that is rated at 60C. The max the conductor is allowed is 55 amps. Since 55 amps is not a standard size breaker you can use a 60 amp breaker only if the calculated load isn't greater than 55 amps. Does that help
Eample of next size up. Say you use a #6 NM cable that is rated at 60C. The max the conductor is allowed is 55 amps. Since 55 amps is not a standard size breaker you can use a 60 amp breaker only if the calculated load isn't greater than 55 amps. Does that help
solar man
Member
- Location
- california
- Occupation
- self emplyed
Yeah I understand that it applies to next size up of the OCPD - this is I guess reverse next size up condition...