12/2 UF wire in 1/2" PVC

[LarryFine]

with small sheet-metal screws.

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[Btbamfan4]

Beam clamps and zip ties are your friend next time.

I can zip tie uf wire to the beams? Good to know. Never ran across this situation before. Use to wiring houses with general crawls and slabs

 

[infinity]

Oh but I see your point. So technically it's not heat even though they say it is? So confusing

There are two separate issues one is fill based on the size of the conductor and the raceway the other is derating due to more than 3 CCC's in the raceway. They really have nothing to do with each other.

 

[Btbamfan4]

Because its underneath a trailer that has a steel bottom. nothing to staple to.

There are two separate issues one is fill based on the size of the conductor and the raceway the other is derating due to more than 3 CCC's in the raceway. They really have nothing to do with each other.

I still dont understand the 3 CCC you keep mentioning. are you saying the ground is a current carrying conductor?

 

[GoldDigger]

I still dont understand the 3 CCC you keep mentioning. are you saying the ground is a current carrying conductor?

He is not saying that you have 3 CCC, he is saying that derating starts at 4 CCC. And the EGC is not a CCC at all. The neutral in an MWBC typically is a CCC, but under specific circumstances (e.g. full boat) it is still not counted for derating purposes.

 

[jim dungar]

Oh but I see your point. So technically it's not heat even though they say it is? So confusing

It is heat related. The number impacts the way the way the conductors twist and turn around each other in the conduit. After 3 conductors it becomes likely that 1 conductor may always find itself stuck below the other conductors and therefore not be able to dissipate heat as well.

As far as using the widest part of the elliptical cable, as infinity said, it is about the cable being free to turn and twist as it is pulled through the conduit without being damaged.

Can you replace at least 1 TA with a cable clamp, so you have a bunch of glued together physical protection items rather than a conduit run?

 

[Btbamfan4]

I could. I have 2 junctions in the crawl at fs boxes If i put 4 in (2 on each box) that would make every end breathable. Would that work?

 

[infinity]

I could. I have 2 junctions in the crawl at fs boxes If i put 4 in (2 on each box) that would make every end breathable. Would that work?

What do you mean by breathable?

 

[Btbamfan4]

How fa

It is heat related. The number impacts the way the way the conductors twist and turn around each other in the conduit. After 3 conductors it becomes likely that 1 conductor may always find itself stuck below the other conductors and therefore not be able to dissipate heat as well.

As far as using the widest part of the elliptical cable, as infinity said, it is about the cable being free to turn and twist as it is pulled through the conduit without being damaged.

Can you replace at least 1 TA with a cable clamp, so you have a bunch of glued together physical protection items rather than a conduit run?

How far of a gap should I leave between each pipe and the fs box? Enough to get a strap within 8 inches?

 

[Btbamfan4]

What do you mean by breathable?

I thought the point of having a cable clamp was to help dissipate heat since it would be enclosed. I'm confused. I'm trying to reply to so many different post lol

 

[Dennis Alwon]

12/2 uf is 463X183 mils according to southwire. So it is .07 sq. in which means it should fit. I used to sleeve 2-12/2 nm in 1/2" but that was a bare

 

[winnie]

Code mixes everything up into a 'simplified' set of rules to follow. If you look for corner cases you will break the physics of things and just get confused.

For example, code requires you to 'derate' if you have too many conductors in a single raceway. But there is no allowance made for the size of the raceway. You could have ten #12 conductors in a 1" EMT or a 6" GRC and code would have the exact same derating requirements.

I believe that the main reason for conduit fill requirements is the issue of being able to insert conductors. Nothing to do with heating or air flow.

IMHO in the situation that you described, the PVC and the UF were actually a good combination. What I suggest you might have done differently was to run the UF from the first box stapled or whatever to get from the box down to the metal below the trailer, then simply gone into a PVC sleeve for the length of the run, then exited the PVC and returned to stapled fastening going to the second box.

-Jon

 

[FionaZuppa]

Right here:

300.17 Number and Size of Conductors in Raceway. The number and size of conductors in any raceway shall not be
more than will permit dissipation of the heat and ready installation or withdrawal of the conductors without damage to the
conductors or to their insulation.

As far as derating for more than 3 CCC's in a raceway the NEC doesn't care if it's ½" or 6" conduit, you get no credit for the additional air in a larger raceway.

Yep, both heat and chafing are accounted for.

 

[FionaZuppa]

Code mixes everything up into a 'simplified' set of rules to follow. If you look for corner cases you will break the physics of things and just get confused.

For example, code requires you to 'derate' if you have too many conductors in a single raceway. But there is no allowance made for the size of the raceway. You could have ten #12 conductors in a 1" EMT or a 6" GRC and code would have the exact same derating requirements.

-Jon

I am not sure it's a mixup. There is no pratical application where you'll have say 25 CCC's and the conduit radius is so large that they all lay flat in the conduit. The common scenario is that some CCC's will be surrounded by others thereby creating a heat "issue", hence derating. Why the # 3, I dunno.

 

[infinity]

Yep, both heat and chafing are accounted for.

And they're two completely different requirements that have nothing to do with each other.

 

[jim dungar]

Enough to get a strap within 8 inches?

sounds good.

In this case your PVC becomes a support and protective sleeve, not a raceway/conduit.

 

[Btbamfan4]

That helps out alot. Greatly appreciate the advice. Thanks to everyone who shared their knowledge!

 

[FionaZuppa]

And they're two completely different requirements that have nothing to do with each other.

That's what is mentioned a few times. Two separate issues wrapped up into the same "fill rules". And at least from my perspective, they do have something to do with each other, at least within that NEC version, because the fill rules tell the reader s/he must run some math on two things when sticking wires and cables in a raceway/conduit.

 

[readydave8]

sometimes there is a gap between top of beam and underbelly so cable can go over beam instead of under

and wooden wedges top of piers to staple to

does not answer your question but may explain why I don't know the answer

 

[Eddie702]

,463 major diameter, .463 x .463 x.7854= area of UF cable=.1684

1/2 schd 40 @53%=.131

no good