Raceways, wireways and JBs oh my...? & derating

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lightmedic

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Dumont, NJ, USA
The background is that we are closing on a home shortly in NJ that needs some love. Given that we have future remodeling plans, I would like to fix the current issues while facilitating future work ease, cleanliness. Having worked for a residential electrician in the Chicago area and fundamentally operating with the go big or go home mentality, I had the notion of running a 6x6 trough down the middle of the house and piping from there. And then derating... As this would be sure to have a prohibitive number of CCCs to avoid serious deratings and thus $$$ in Cu:

Having scrolled the archives and NEC, it is clear that all of the derating applies only to raceways, not JBs. Aside from the prior post about a JB every 24" (which I find expensive and "wrong" even if "acceptable" to code) or derating the heck out of wires in the name of making it pretty, are there any options?

Questions that have been percolating:

0) All of these questions are also assuming that there is nothing preventing wireways from residential use... Can't think of why it would be, but you never know.

1) Options

2) Where is the line between raceway, wireway and JBs? Article 100 p70-29 of 2008.
2a) For the Wireway/JB line, my brain wants to draw the line either between a solid box and a wireway with fastener attached ends OR a wireway with fastener attached ends and a wireway assembled with a splice. THis does not address a differential wire raceways...

3) What is the reasoning/engineering behind the derating to the degree they do when in a 4x4, 6x6 wireway and not a JB? Sure in a pipe, but if you are filled at or below 20% even there, why the degree of derating? Why are multiple branch circuits somehow worse than a couple pieces of feeder? The total available current is no different...

4) Why the 45% from table 310.15(B)(2)(a) vs no derating under 30 CCCs from 376.22(B)? They appear to be contradictory, what am I missing?

5) Can one modify a wireway/trough with, say, an outlet, that somehow magically transforms the wireway to a junction box.

6) What/where is the code pertaining to "required spacing" re: "installed without maintaining spacing for a continuous length" of 310.15(B)(2)(a)?
6a) What is available to maintain said spacing?

7) And for the theater and entertainment folks, other than the higher temp insulation ratings, how is utilizing a wireway for branch circuit distribution that exits via a pipe different than Connector strips 520.2 & 520.42 with the branches exiting in extra hard service duty rated cordset?

Thanks folks.
Dan
 
I strongly urge you not to reinvent the wheel.

Hire a contractor who knows home wiring. Just like a residential electrician would be out of place on a stage you will be out of place wiring a home.

There is no reason to be talking about wireways or article 520 at all in regards to home wiring.
 
Design

Design

A few years ago I saw a plastic trough/wireway that was designed for residential use. I can't remember the company nor a good Google search for it. I think it was expected to be filled with NM cable and did not require derating.

If you place the feed in the center of the run and do some design you may able to work out a good solution. In metal wireways you can have up to 30 Current Carry Conductors at any given cross section without derating.

If you run a few conduits to points in the wireway the CCC count can be kept below 30. And you can put 9 CCC #12 THHN in a conduit without having to change 20A CBs.
 
lightmedic said:
The background is that we are closing on a home shortly in NJ that needs some love. Given that we have future remodeling plans, I would like to fix the current issues while facilitating future work ease, cleanliness. Having worked for a residential electrician in the Chicago area and fundamentally operating with the go big or go home mentality, I had the notion of running a 6x6 trough down the middle of the house and piping from there. And then derating... As this would be sure to have a prohibitive number of CCCs to avoid serious deratings and thus $$$ in Cu:

Having scrolled the archives and NEC, it is clear that all of the derating applies only to raceways, not JBs. Aside from the prior post about a JB every 24" (which I find expensive and "wrong" even if "acceptable" to code) or derating the heck out of wires in the name of making it pretty, are there any options?

Questions that have been percolating:

0) All of these questions are also assuming that there is nothing preventing wireways from residential use... Can't think of why it would be, but you never know.

1) Options

2) Where is the line between raceway, wireway and JBs? Article 100 p70-29 of 2008.
2a) For the Wireway/JB line, my brain wants to draw the line either between a solid box and a wireway with fastener attached ends OR a wireway with fastener attached ends and a wireway assembled with a splice. THis does not address a differential wire raceways...

3) What is the reasoning/engineering behind the derating to the degree they do when in a 4x4, 6x6 wireway and not a JB? Sure in a pipe, but if you are filled at or below 20% even there, why the degree of derating? Why are multiple branch circuits somehow worse than a couple pieces of feeder? The total available current is no different...

4) Why the 45% from table 310.15(B)(2)(a) vs no derating under 30 CCCs from 376.22(B)? They appear to be contradictory, what am I missing?

5) Can one modify a wireway/trough with, say, an outlet, that somehow magically transforms the wireway to a junction box.

6) What/where is the code pertaining to "required spacing" re: "installed without maintaining spacing for a continuous length" of 310.15(B)(2)(a)?
6a) What is available to maintain said spacing?

7) And for the theater and entertainment folks, other than the higher temp insulation ratings, how is utilizing a wireway for branch circuit distribution that exits via a pipe different than Connector strips 520.2 & 520.42 with the branches exiting in extra hard service duty rated cordset?

Thanks folks.
Dan
Click to expand...

We have not developed the "perfect" conductor, all conductors have some resistance. When current flows through a resistance heat is given up. Several small conductors carrying a high current for the size will create more heat then a larger feeder that is sized for the sum of all those smaller conductors.

NEC is not perfect with the process either, but rather uses a process that has some compromise to make calculations somewhat simpler overall and consistent over several different applications, plus it wants to be a little on the conservative side for safety reasons.

Load diversity in a dwelling is often not all that great, and you very well could put a lot of conductors in one raceway, wireway, bundle, or whatever and never generate any heat significant enough to cause much problem. Put same number of conductors in close proximity in a commercial or industrial setting where loads are more continuous and you will have more heat in those applications. NEC does not really give us permission to determine what that diversity is going to be and make compensation for it though. You ever been in a commercial or industrial panelboard and noticed warm to almost hot breakers, or even feel warmth on raceways? You seldom see that in a dwelling because there is not the same load diversity. If you do notice something warm or even almost hot, (in the absence of something that is failing) about the only thing in a dwelling that gets like that is heating or cooling equipment circuits, and more so cooling then heating, because it is about the only load in a dwelling that will run continuously for very long.
 
Really?

Really?

iwire said:
I strongly urge you not to reinvent the wheel.

Hire a contractor who knows home wiring. Just like a residential electrician would be out of place on a stage you will be out of place wiring a home.

There is no reason to be talking about wireways or article 520 at all in regards to home wiring.
Click to expand...

:happyno:
Beg to differ and guess we skipped the third line? When I referenced my electrical work in Chicago I was doing so to indicate my leanings towards EMT and away from NM. As it turns out, I am quite qualified in both stage and residential wiring. More than enough to explain electricity to the "Master Electrician" whose license I was working "under".

My reference to 520 was to highlight a code spec difference between two essentially identical products (long metal wire chase with lots of CCCs), one of which explicitly does not attend to the derating. Connector strips can easily have (20+) circuits with two or more outlets individually home run back to the junction box, thus (80+ CCCs), all of which have crazy harmonics associated with SSR dimming requiring individual neutrals. Granted they are rarely on when time averaged over a day, but when they are on, it can be 80% of them at various levels (making it worse with the harmonics...) Part of why we entertainment folk run 3phase six wire - with up to 1.7 times the unballanced neutral current, we can need that extra copper. I have previously had a wonderful conversation with an inspector who reviewed sound stage drawings on the side, yet had no background to understand the configuration. He was quite happy for the education, as was I for the education he provided on a detail question I had posed.

Unless you happen to be "the one", we all have different knowledge and experiences from which we draw our respective expertise. Pardon my assumption if we were here to ask and share rather than chastise and berate, especially when attempting to expand one's knowledge by requesting other perspectives and expertise. Pleased to be checking the caviler "I'm a professional". Better discovered than professed (albeit by inference) and does nothing but raise red flags, induce fear, and send my less than athletic physique running the other direction - quickly.
 
kwired said:
We have not developed the "perfect" conductor, all conductors have some resistance. When current flows through a resistance heat is given up. Several small conductors carrying a high current for the size will create more heat then a larger feeder that is sized for the sum of all those smaller conductors.

NEC is not perfect with the process either, but rather uses a process that has some compromise to make calculations somewhat simpler overall and consistent over several different applications, plus it wants to be a little on the conservative side for safety reasons.

Load diversity in a dwelling is often not all that great, and you very well could put a lot of conductors in one raceway, wireway, bundle, or whatever and never generate any heat significant enough to cause much problem. Put same number of conductors in close proximity in a commercial or industrial setting where loads are more continuous and you will have more heat in those applications. NEC does not really give us permission to determine what that diversity is going to be and make compensation for it though. You ever been in a commercial or industrial panelboard and noticed warm to almost hot breakers, or even feel warmth on raceways? You seldom see that in a dwelling because there is not the same load diversity. If you do notice something warm or even almost hot, (in the absence of something that is failing) about the only thing in a dwelling that gets like that is heating or cooling equipment circuits, and more so cooling then heating, because it is about the only load in a dwelling that will run continuously for very long.
Click to expand...


The engineer in me is much happier with a supporting concept! Thank you!
Still don't like the code restrictions, but know I understand the origins of what I dislike. Again, Thank you!
 
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