sub panel in attic

[Dennis Alwon]

Here's an article with some info on ambient temperature and the temperature relationship with circuit breaker operation.

http://www.ab.com/en/epub/catalogs/12768/229240/471158/1213081/5725120/tab2.html

So in your opinion do you think the ambient temp in an attic is an issue?

 

[electricmanscott]

The only thing is the "protection of wires" you may have to put sheet rock in that one bay area. Where the wires would be accessible....IMO

If I have 10 wires that I know will be exposed to physical damage I cover them up. I'll use a small piece of plywood or sheet rock.
That's no different then wiring a garage that will some day be sheet rocked. The wires must be protected IMO.

I done a service call this week. The owner had a full basement. He had put an entire office down thier, tv room, kids toys around, etc... with out ever sheetrocking the walls.
That was my point...

The things I highlighted are two VERY different things. The NEC does not require all exposed romex to be covered.

This is how rumors get started.

 

[jetlag]

I think its legal but question it as saving money.

Yes I think so it will save long runs of at least 6 12-2 , 3 10-2 , 1 8-2 plus the labor to run them these are all cu , the 100 a alum ser is not expensive at all and I allready have 100 amp subs

 

[jetlag]

The only thing is the "protection of wires" you may have to put sheet rock in that one bay area. Where the wires would be accessible....IMO

good point

 

[Buck Parrish]

The things I highlighted are two VERY different things. The NEC does not require all exposed romex to be covered.

This is how rumors get started.

Your right I could have worded it differently. I think most of us do this or something similar any way.
Wires should follow and be stapled to joices or running boards instead of perpindicular. JMHO

 

[infinity]

So in your opinion do you think the ambient temp in an attic is an issue?

According to the NEC no, unless you want to throw some obscure listing requirement in the mix. Then Article 110 would come into play.

 

[goldstar]

I just got tagged for an attic 100 amp sub-panel that I installed about a year ago. The owner finally got around to calling for an inspection. I ran 100 amp SER cable and installed a 2-pole 90 in the main. The inspector told me I had to use the 60 degree column for # 2 aluminum and made me change the breaker to a 2-pole 80. Another $50.00 down the drain.

 

[electricmanscott]

I just got tagged for an attic 100 amp sub-panel that I installed about a year ago. The owner finally got around to calling for an inspection. I ran 100 amp SER cable and installed a 2-pole 90 in the main. The inspector told me I had to use the 60 degree column for # 2 aluminum and made me change the breaker to a 2-pole 80. Another $50.00 down the drain.

Shoulda did it right in the first place.

 

[goldstar]

Shoulda did it right in the first place.

I know. I wish I could go back 25 years in time and know what I know now !!!:roll:

 

[LEO2854]

I just got tagged for an attic 100 amp sub-panel that I installed about a year ago. The owner finally got around to calling for an inspection. I ran 100 amp SER cable and installed a 2-pole 90 in the main. The inspector told me I had to use the 60 degree column for # 2 aluminum and made me change the breaker to a 2-pole 80. Another $50.00 down the drain.

I wonder why you did not call for inspection after you finished the install?
why would you leave it up to the home owner?

 

[jetlag]

I just got tagged for an attic 100 amp sub-panel that I installed about a year ago. The owner finally got around to calling for an inspection. I ran 100 amp SER cable and installed a 2-pole 90 in the main. The inspector told me I had to use the 60 degree column for # 2 aluminum and made me change the breaker to a 2-pole 80. Another $50.00 down the drain.

If panel had been in basement or main house could the main have been 90 or 100 amp ? I assume the ahj dropped to 80 because of attic , was it because box in attic and not the ser in attic or both ?

 

[infinity]

If panel had been in basement or main house could the main have been 90 or 100 amp ? I assume the ahj dropped to 80 because of attic , was it because box in attic and not the ser in attic or both ?

It was becuase the feeder has to be sized according to the 60? C ampacity of #2 AL which is 75 amps in Table 310.16. The next standard size OCPD is 80 amps which is permitted to be used if the calculated load is 75 amps or less.

 

[goldstar]

I wonder why you did not call for inspection after you finished the install?
why would you leave it up to the home owner?

I usually don't call for the inspections. Most of the inspectors in my area inspect for more than one town (budget cuts). This particular inspector inspects on tuesdays and thursdays between 12:00 PM and 3:00 PM. The homeowner has to be home to let him in to inspect anyway. With jobs and prices being the way they are these days I'm certainly not going to wait around for 3 hours for an inspector to show up. The reason this went on for as long as it did was because the HO procrastinated so long that the town called him and told him the permit would expire and he would have to re-file and pay for a new permit. I guess that got him moving.

 

[goldstar]

It was becuase the feeder has to be sized according to the 60? C ampacity of #2 AL which is 75 amps in Table 310.16. The next standard size OCPD is 80 amps which is permitted to be used if the calculated load is 75 amps or less.

The sad part of this is that the HO only has (2) 20 amp circuits in the sub-panel presently but wanted to have capacity for add'l circuits in the future. He never mentioned what the add'l loads might be but I know he has (2) daughters. That should explain about 40 amps worth right there.:roll:

 

[jetlag]

It was becuase the feeder has to be sized according to the 60? C ampacity of #2 AL which is 75 amps in Table 310.16. The next standard size OCPD is 80 amps which is permitted to be used if the calculated load is 75 amps or less.

I never thought about it much, but use2 aluminum 2-2-2-4 is the standard for 100a underground feeder , the 100a is a 90 deg rateing , everyone on here says cant rate with 90 deg because of terminals . Im sure big blue and orange didnt decide on the #2 size on their own, all they stock is 2-2-2-4 for 100a with 100 amp breaker to 100a inside panel and 4/0 4/0 1/0 4 use2 alum for 200a with 200a main .. Is every one sure about the terminals in a standard outside disconnect and an inside panel cant use the 90 a rating. If so every supply house and install i know of is all wrong , I just dont believe that , I think the post that argue the 90 deg terminal thing are missing something some where ,something is wrong somewhere. I have done to many mobile home underground feeder connections to count and never been flagged for the breaker or conductor size. I am not refering to the # 2 ser I know that is 60 c

 

[Dennis Alwon]

I never thought about it much, but use2 aluminum 2-2-2-4 is the standard for 100a underground feeder , the 100a is a 90 deg rateing , everyone on here says cant rate with 90 deg because of terminals . Im sure big blue and orange didnt decide on the #2 size on their own, all they stock is 2-2-2-4 for 100a with 100 amp breaker to 100a inside panel and 4/0 4/0 1/0 4 use2 alum for 200a with 200a main .. Is every one sure about the terminals in a standard outside disconnect and an inside panel cant use the 90 a rating. If so every supply house and install i know of is all wrong , I just dont believe that , I think the post that argue the 90 deg terminal thing are missing something some where ,something is wrong somewhere. I have done to many mobile home underground feeder connections to count and never been flagged for the breaker or conductor size. I am not refering to the # 2 ser I know that is 60 c

Jetlag, for a residence #2 aluminum is legal for 100 amps based on T.310.15(B)(6). This is why the big boxes carry it. I don't think they ever caught up to the fact that now as a feeder se xcable is rated 60c. The fact is that this does not affect USE cable which still has the 90C but must be used at 75C.

I am not sure what you don't understand about 90C termnals because there are very few terminals out there that are rated 90C- just check your equipment.

You mention mobile home UG feeders- USE #2 aluminum is perfectly okay for an UG feeder to the home at 100 amps. Maybe I am missing your point.

 

[don_resqcapt19]

This Square D document shows the trip points of their breakers when they are operated outside of the 25? to 40?C range.

 

[infinity]

I never thought about it much, but use2 aluminum 2-2-2-4 is the standard for 100a underground feeder , the 100a is a 90 deg rateing , everyone on here says cant rate with 90 deg because of terminals . Im sure big blue and orange didnt decide on the #2 size on their own, all they stock is 2-2-2-4 for 100a with 100 amp breaker to 100a inside panel and 4/0 4/0 1/0 4 use2 alum for 200a with 200a main .. Is every one sure about the terminals in a standard outside disconnect and an inside panel cant use the 90 a rating. If so every supply house and install i know of is all wrong , I just dont believe that , I think the post that argue the 90 deg terminal thing are missing something some where ,something is wrong somewhere. I have done to many mobile home underground feeder connections to count and never been flagged for the breaker or conductor size. I am not refering to the # 2 ser I know that is 60 c

IMO you're confusing two different requirements. This thread is about a sub panel which would require the use of SE cable at it's 60? C ampacity regardless of the temperature rating of it's terminations. If you were supplying the total load to a dwelling unit then the table that Dennis posted. T310.15(B)(6) would permit the same #2 Al SE cable to used at a higher ampacity.

310.15(B)(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.

338.10(B)(4) Installation Methods for Branch Circuits and Feeders.
(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334.
FPN: See 310.10 for temperature limitation of conductors.

334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).

 

[Dennis Alwon]

This Square D document shows the trip points of their breakers when they are operated outside of the 25? to 40?C range.

So basically as you get to the 40C range the ampacity of a 20 amp breaker is derated by just a few amps. Is that correct-- talking QO breaker here.

 

[don_resqcapt19]

So basically as you get to the 40C range the ampacity of a 20 amp breaker is derated by just a few amps. Is that correct-- talking QO breaker here.

At 40?C it trips at the handle rating. At 60?C it looks like it would trip at about 17 amps and at -10?C at about 27 amps.