Question ampacity

Status
Not open for further replies.
C

codequestion

Banned
Location
MD, USA
I have 100 amp circuit breaker and feeder cables are from the circuit breaker sized #2 AL which is 90 amps. Do feeders have to be sized #1 AL (100 amps) or #2 AL (90 amps) is ok?

Sent from my SM-G935U using Tapatalk
 
You need to use a larger conductor since 90 amps (#2) is a standard size in 240.6 and you cannot use the next size up rule.
 
codequestion said:
Correct it says to ise for 120/240V however ehat table to use if voltage is 120/208v?

Sent from my SM-G935U using Tapatalk
Click to expand...


Read 310.15(B) It tells you the long answer to your question. And not being mean, but the way you asked your question in pieces is a PERFECT example of why the short answer doesn't work. Ampacity calculation is based on numerous factors. All the answers you should need to at least give it a try are in 310.15(B) Then it is merely getting it right or making a mistake.
 
Strathead said:
I answered him too. And you fell in to his trap. Every time he gets an answer he modifies the criteria. For example next "Oh, what if it is fed overhead?"
Click to expand...
Understand ampacity deoends on lot of factors. The problem is I am recalling from my memory possibly at night time or afternoon but the engineering plans are in office. I do research before I post but am not able to find correct answers complex code and posting when i am in office may take while to get answers. This way I have some of the answers and do research when I am in office. Please be specific.

Sent from my SM-G935U using Tapatalk
 
codequestion said:
Understand ampacity deoends on lot of factors. The problem is I am recalling from my memory possibly at night time or afternoon but the engineering plans are in office. I do research before I post but am not able to find correct answers complex code and posting when i am in office may take while to get answers. This way I have some of the answers and do research when I am in office. Please be specific.

Sent from my SM-G935U using Tapatalk
Click to expand...

I was sort of teasing.
 
T310.15(B)(16) is the base that nearly always applies, (B)(7) is an allowance for a special condition, you can always still use (B)(7) even if you meet the allowance conditions.
 
qcroanoke said:
If it's SE cable I believe at one time it was good for 100 amps. That's why I ask if it's existing
Click to expand...

The 120/240 volt limitation has been in place as long as I can remember. With a 120/208 system the grounded conductor is considered a current carrying conductor so you have 3 conductors producing heat. With a 120/240 volt system you only have the equivalent of 2 conductors producing heat.
 
Status
Not open for further replies.
Top