Mrfixit
Member
- Location
- Jacksonville, FL
Is a Main breaker needed for a sub panel that is fed from another floor?
Correct, the feeder panel has a 100 amp breaker dedicated to the sub panel I am installing. Thanks
The new panel is a 100 amp Square D w/ bolt in breakers. I ran 2" EMT between them with 2 AWG THHN for the feeds and #8 ground.
Could this be a problem with 250.122(B) or are your terminations only rated for 60? C?
I don't see where the #8 will be a problem. Do you suggest I increase it to a #6? There are 4 other circuits in the feeder panel wired this same way. Not that they are right, I'm just trying to follow code as I see it.
You don't even need the egc with emt but #2 at 75C is required for 100 amp. If you install an EGC then it only needs to be #8 unless we are talking aluminum and not copper.
a #3 wire is rated at 100a 75C cu. Why is a #2 required?
It is not required- bad choice of words-- It is rated 115 so it is good for 100 amp breaker so I don't see it as an upsize
My thinking is it is the ONLY example of upsizing... If you COULD use a smaller wire, than you are using a bigger wire right? What else would be upsizing?
That is the problem with 250.122(B). Do we read the 60C or 75C column. Either size is appropriate so I don't see the issue but who knows...
For instance if I have a load of 55 amps I can use #6 nm on a 60 amp circuit breaker however if I want to allow for a true 60 amp circuit I would have to use #4 NM. So is that upsizing-- remember I can use a DP 70 but they cost a bit more than a DP60.
Is the idea that for a 100a ampacity you could have used a #3 ungrounded wire? and #8 EGC. But you increased it to a #2, The increase is about a 17% increase in area so you have to use a EGC wire with at least a 17% increase in area also? Forcing you to increase to a #6 EGC?
Am I getting the gest correct?
I think if you increased from the minimum required (#3 cu) than you have to increase the EGC from it's minimum required (#8 cu)
What do you guys think?
I think you are a little off on the increase from #3 to #2.
#2 has a cir. mil area of 66360
#3 has a cir. mil area of 52620
66360/52620=1.26
according to my calculations