Subpanel question 100A/NEC 2017

[ED26]

Hello, Currently have 200A main disconnect outside home (this is considered the MAIN PANEL).

From there 4/0 SER AL feeds panel (SUB PANEL) in utility room Siemens 200A, 40 Space.

Would like to run 100A from 200A utility room subale panel to att garage.

Per the NEC 2017; can I run SER AL 1-1-1-3 at the 75C rating due to the terminals rated on panel being 75C, or does it have to be rated at 60C allowable ampacity which would force 1/0 SER AL.

The electrician I had come quote, said I can use SER AL 2-2-2-4 for the 100A subpanel att. gar., but from my understanding this is only good if it feeds the entire 'Dwelling'. I had a second electrician come look, and he said SER 2 AL is fine for 100A sub in att. gar.

 

[pattenp]

The 1-1-1-3 Al SER is what you need for 100A. 2-2-2-4 Al SER is only good up to 90A as a branch feeder. You can use the 75C rating only if the SER is not run within insulation for more that 10% of it length or a max of 10ft in insulation. Your electrician is mistaken, the #2 Al at 100A is only when used as the main service supplying the entire load to a dwelling.

 

[Norcal]

The tables allowing 2AWG AL to be used for 100A is long gone it is now determined by load calculations but both electricians need some schooling on wire sizes because they are both wrong.

 

[ED26]

The 1-1-1-3 Al SER is what you need for 100A. 2-2-2-4 Al SER is only good up to 90A as a branch feeder. You can use the 75C rating only if the SER is not run within insulation for more that 10% of it length or a max of 10ft in insulation. Your electrician is mistaken, the #2 Al at 100A is only when used as the main service supplying the entire load to a dwelling.

Thank you - good reason I did not hire this 'licensed' electrician or the other 'licensed' electrician who said 2 SER AL is fine. Not sure what is going with the trades nowadays...

The cable will run 50' in crawl, 8' up wall that has kraft face R13 insulation, 25' in gar. att (will sit on top attic truss above kraft R-19 faced insulation / not touching or within insulation), and down 5' wall that has kraft insulation to panel. So total of 88' cable, and of that 88' - 13' will be touching insulation, that is 15% but not continuous insulation contact, I am estimating the lengths now, but I am close to the 10% or 10' rule..

 

[AntonLargiader]

Apparently there are inspectors who still accept 2-2-2-4 for 100A. We had that in a thread here maybe a year ago and while some of the forum members were all bent out of shape about it, it was simply the case and if your electricians know that the guy inspecting their work accepts that, then maybe that's what's going on.

 

[pattenp]

In contact with insulation is not a problem, it just can't be encased/buried within insulation. So your 88' can't have more than 8.8' of it running inside of insulation. The 10' limit comes into play once you're over 100' of run.

 

[ED26]

In contact with insulation is not a problem, it just can't be encased/buried within insulation. So your 88' can't have more than 8.8' of it running inside of insulation. The 10' limit comes into play once you're over 100' of run.

Thank you for your help.

It will not be encase or buried within insulation. Just in contact R13 once it goes up the stud cavity on first wall, then in contact with R13 when down other wall into the Subpanel.

I'll run 2-2-2-4 SER AL and protect with 90AMP (75C) breaker or if I can find locally 1-1-1-3 SER AL protect with 100AMP (75C).

 

[wyliesdiesels]

Apparently there are inspectors who still accept 2-2-2-4 for 100A. We had that in a thread here maybe a year ago and while some of the forum members were all bent out of shape about it, it was simply the case and if your electricians know that the guy inspecting their work accepts that, then maybe that's what's going on.

Inspectors can be wrong as well.

Just because the inspector accepts it or passes it, doesnt mean it follows code which is 90a max for #2 al. Dont know why this is so hard to follow and beat to death all the time. The ampacity table is at our disposal. Its literally right there in the code book

Theres another current thread on here where an inspector passed a bonded 4-wire subpanel. WHOOPS. But with your logic, since the inspector passed it, its ok.

 

[dcg9381]

The 1-1-1-3 Al SER is what you need for 100A. 2-2-2-4 Al SER is only good up to 90A as a branch feeder. You can use the 75C rating only if the SER is not run within insulation for more that 10% of it length or a max of 10ft in insulation. Your electrician is mistaken, the #2 Al at 100A is only when used as the main service supplying the entire load to a dwelling.

I agree with this. Just ran 2-2-2-4 to a shop. 90A is the limit when considering rises in the temperature within conduit.

I'd probably not make the jump in wiring size to get another 10A though.. But your application may be different.

 

[alfredeneuman]

The tables allowing 2AWG AL to be used for 100A is long gone it is now determined by load calculations

If you do the load calculations (@83%), it works out to be the same sizes as on the old table though.

 

[mike93lx]

I agree with this. Just ran 2-2-2-4 to a shop. 90A is the limit when considering rises in the temperature within conduit.

I'd probably not make the jump in wiring size to get another 10A though.. But your application may be different.

conduit has nothing to do with the 90a rating