Code compliance.

Status
Not open for further replies.

electric_instructor

Senior Member
Question?
Your wiring an addition onto a HUGE home. However this is only a "trophy" room. BUT, it includes a "plywood" backed wall, which is intended to support an "elephants head" trophy!

You install a 12 circuit subfed panel, and the "feeder" to it. Then the "general contractor pressures you, and the inspector allows the "closing "of the wall.

You MUST allow for the "future" in order to feed the "branch circuits", from the panel.

SO, - you design a 2" EMT chase from the top of the panel, reaching beyond the upper wall plate, so that the wall can be closed. Sound familiar?

Thing is this! The panel "top" is 6' above the floor, and the wall plate is 8' 2" above the floor.

You have 11, 120 volt circuits fed using 12/2 NM cable, and it is feeding into an attic, where the temperature is expected to reach at least 125 degrees F.

What is the actual "maximum allowable ampacity" of the installed conductors?

:shock:
 

iwire

Moderator
Staff member
Location
Massachusetts
Given your description you could not simply snake the NM down the 2" EMT you will need to place a box at the top of the EMT which will need to remain accessible.

As far as how many conductors can you install?

As many as will fit once you apply the derating rules.

With 15, 20 and 30 amp circuits you can generally install 9 current carrying conductors in one raceway before you have to start up sizing the conductors.

A few 1" EMTs would have been a more practical choice.
 

memyselfandI

Senior Member
I'll try to answer what you asked and I hope I got this right.
11 amps is what I came up with using Table 310.15(B)(2)(a).
16 amps is what I came up with using Table B310.11.
It is unfortunate that these people are in such a hurry to make themselves look good at the expense of making you look bad. It amazes me that when an electrician walks on the job he or she is all ready behind and the first thing that is brought up is when can they close the walls. We always have the most work to do but are never allowed the courtesy to do our job. I always tell the contractor that he can cover anything he wants to but that I am not finished and the inspector will make you tear it down. You should be allowed to do your job as specified in the contract. This instance requires you to have to go in the attic to complete your job costing more time and money and not receiving compensation for the unnecessary work. IMO.
 

iwire

Moderator
Staff member
Location
Massachusetts
memyselfandI said:
I'll try to answer what you asked and I hope I got this right.
11 amps is what I came up with using Table 310.15(B)(2)(a).
16 amps is what I came up with using Table B310.11.

How about sharing how you came up with 11 and 16 amps?

memyselfandI said:
It is unfortunate that these people are in such a hurry to make themselves look good at the expense of making you look bad.

This is an electrical forum, the opening poster asked a question.

I gave my answer based on my understanding of the NEC.

If that is or is not the answer you or the OP wanted is of no consequence.

By the way, your profile is empty are you an engineer?

If not you can forget about B310.11

B.310.15(B)(1) Formula Application Information.
This annex provides application information for ampacities calculated under engineering supervision.
 

memyselfandI

Senior Member
Well I guess Mr. iwire told me. I can see that at the times we both posted our reply we get up pretty early and some of us tend to be a little cranky. As to how I came up with those answers, how do you think I came up with them? Was the anwers correct or incorrect? What did you come up with? The question was posted, I answered it to the best of my ability as you did. I was merely referring to the pressure the individual was getting from the GC to close up. Sharing some electrical info to a fellow electrician. As for B310.11, you are correct and I appreciate you pointing that out to me. 8)
 
MemyselfandI
I like you name.

The poster also mentioned the attic ambient temperature of 125 F. Did you take that into account. See 310.10 and both of the FPNs that follow. I know the FPNs are not mandatory, they are there to give direction as to the language in 310.10.

Also, you get more bees with honey :wink:

I do not think anyone was trying to make the OP look bad, that is a perception people tend to have when they feel paranoid.
 

iwire

Moderator
Staff member
Location
Massachusetts
memyselfandI said:
As to how I came up with those answers, how do you think I came up with them?

If I knew I would not have asked.

You see we are a friendly bunch here and we help each other out by explaining how we got our results. :p
 

stew

Senior Member
the way I would make this calculation is to use the 90 deg table staring at 30 amps derating by 50 % for 11 conductors to get to 15 and then using the temp tables further derate by .76 which calculates to an ampacity of 11.4 amps. Now what size breaker do I use?. Better to use a couple 1 1/4 inch chases in my mind. then with 30 amp start you get 80% drate to 24 and then a temp derate at .76 to get to 18 amps and a 15 amp breaker. the only way I can see to get the required 20 amp rating is to use # 10 nm. I think I am using the correct calculations no?
 

RUWired

Senior Member
Location
Pa.
Stew,11 12/2 circuits = 22 conductors.Derate is 45%.Then .76.Don's answer is correct.(11a).There are a lot of ways out,including taking down the finished surface,which is what i would do.
Rick
 

jes25

Senior Member
Location
Midwest
Jim W in Tampa said:
You are not allowed to use this 2 inch emt for running that romex into a panel.Is that what your wanting to do ?

Why not? Reference please. Assuming you derate.
 

jwelectric

Senior Member
Location
North Carolina
jes25 said:
Jim W in Tampa said:
You are not allowed to use this 2 inch emt for running that romex into a panel.Is that what your wanting to do ?

Why not? Reference please. Assuming you derate.

321.5(C) Cables. Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure.

Exception: Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length, provided all of the following conditions are met:


A pipe of any kind or size installed with a flush mounted panel is a violation.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
It is not an approved way to enter a panel with romex.How will you fasten the romex if we did allow this ?10 years ago many of us used this method for all the HR going into a panel.Not any more
 
Status
Not open for further replies.
Top