# Classroom prewire pics



## 3rdgenwireman (Dec 12, 2010)

De-rating?


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## Nuzzie (Jan 11, 2012)

3rdgenwireman said:


> De-rating?


Not really needed. You could treat it as being completely surrounded in insulation, and for the load each of these will be seeing, it's completely fine.


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## niteshift (Nov 21, 2007)

May be allowed cause its a prefab type of install?
Approved means for securing romex (looks like romex) in the attic pic is the velcro? Like said earlier, derating does not apply there? 
That is alot easier/quicker then staples and standoffs.:thumbup:


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## 480sparky (Sep 20, 2007)

Nuzzie said:


> Not really needed. You could treat it as being completely surrounded in insulation, and for the load each of these will be seeing, it's completely fine.


The load intended has no bearing on derating. You could have a 4w night light on each circuit, and you would still need to derate.

310.15(B)(3)(a).


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## Nuzzie (Jan 11, 2012)

niteshift said:


> May be allowed cause its a prefab type of install?
> Approved means for securing romex (looks like romex) in the attic pic is the velcro? Like said earlier, derating does not apply there?
> That is alot easier/quicker then staples and standoffs.:thumbup:


We just call it TPS here, heh. We used velcro (yes it's approved, and it's all wrapped over itself a fair bit, not dangling by a tiny bit holding it up) because using the catenary wire, if you want to add or remove a cable at a later date it's easier than cable ties (though no doubt that nice stacking would get ****ed in the ass)


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## 360max (Jun 10, 2011)

that's bundling and you must derate

edit: just realized you are from New Zealand, different country different rules.


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## Nuzzie (Jan 11, 2012)

480sparky said:


> The load intended has no bearing on derating. You could have a 4w night light on each circuit, and you would still need to derate.
> 
> 310.15(B)(3)(a).


Fair enough. I feel I kind of explained myself poorly. Derating that cable for completely being surrounded by thermal insulation would take it's max load to 14A, and these cables will be seeing two computers, 2 monitors. That's it, lucky to get to half of that, and obviously these are not or going to be surrounded by insulation. They will be protected at the switchboard with appropriately sized RCBO's (15A I believe, 10mA trip)

Unfortunately I cannot refer to your NEC code

If I am mistaken in any way, I would love to be corrected.


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## MDShunk (Jan 7, 2007)

Damn that looks like a lot of work. That same install, in the US, would just have those cables laid on top of the bottom chord of the roof trusses.


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## Cletis (Aug 20, 2010)

480sparky said:


> The load intended has no bearing on derating. You could have a 4w night light on each circuit, and you would still need to derate.
> 
> 310.15(B)(3)(a).


The load has no bearing?? Huh :blink:


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## 480sparky (Sep 20, 2007)

Cletis said:


> The load has no bearing?? Huh :blink:


Where in that code reference does it mention the load?

A: It doesn't.


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## HARRY304E (Sep 15, 2010)

Cletis said:


> The load has no bearing?? Huh :blink:


And.??:blink:


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## Nuzzie (Jan 11, 2012)

Cletis said:


> The load has no bearing?? Huh :blink:


Intended load =\= load, all the time. 

Just because there is a small intended load doesn't mean that you shouldn't resize the circuit breaker to account for the decrease is current carrying capability of the cable.


If there is more to it, I am all ears. Not even an apprentice yet so would like to be gaining as much knowledge as I can.

Edit: In regard to the above, wouldn't you still be taking the load into consideration. If you've got something that under normal situations would be fine on 2.5mm^2, however due to needing to derate the cable because of the circumstance you might find that 2.5mm^2 is no longer adequate and you need to size a larger cable for it.


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## BLM (Jan 26, 2012)

Looks good when I run power cir. I alway put it on a 16amp combo and lighting on a 1 mm I use a 6amp combo and use 10amp on my 1.5 mm keep up the good work bro.


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## niteshift (Nov 21, 2007)

Nuzzie said:


> We just call it TPS here, heh. We used velcro (yes it's approved, and it's all wrapped over itself a fair bit, not dangling by a tiny bit holding it up) because using the catenary wire, if you want to add or remove a cable at a later date it's easier than cable ties (though no doubt that nice stacking would get ****ed in the ass)


 Yes it looks neat and all, but we're just saying those methods wouldn't fly here.

By the way you said this is students, marking crosshairs on the top plates. Just tell them to make holes in center of boards. 

Reason middle hole didn't get used " top boards meet there has the nails in the way". 
Our holedrills/holehogs use bits known as nail eaters, they won't eat very many before replacement/resharpening.:laughing:

Velcro for low voltage yes. Just not 120/240.
Cable ties here, only where approved, some places are real strict about cable ties on conductors... I know we all use em, last time I looked they were not approved as a fastening means for wiring. 

Actually, once was gonna be turned down on inspection during a basement remodel because I used cable ties to support the romex in the free space between the block and backside of the 2x4's, useing nails for standoffs. While not agreeing with him, I did it the way he specified. No cable ties, can use tiewire though, like for rebar, did it, got the green sticker and all was good. Never used tiewire to fasten romex after that. Cable ties were good enough for all the other inspectors in that co. and 7 other jurisdictions.


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## BLM (Jan 26, 2012)

Here in Australia I only use Velcro on data and cable ties on the 240v. 
I would really like to come over and see how you guys do things.


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## LightsOn81 (Jan 6, 2012)

Americans we are good fast not always so neat and friggin arrogant :eek


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## BuzzKill (Oct 27, 2008)

Aren't those Arlington spacers? I wouldn't think derating is necessary at all.


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## Cletis (Aug 20, 2010)

*?*



480sparky said:


> Where in that code reference does it mention the load?
> 
> A: It doesn't.


I don't know. I haven't bought a code book yet. But, it has a huge bearing in the bundling and derating of cables.


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## niteshift (Nov 21, 2007)

BLM said:


> Here in Australia I only use Velcro on data and cable ties on the 240v.
> I would really like to come over and see how you guys do things.


Yeah I would love to come down there.


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