Conduit fill and Jumper for multiple conductors - NEC code

[wwhitney]

Whatever you call it, the pipe in the photo definitely isn't mechanically integrated to the array (or anything else!) and thus the conductors aren't within the array. If the pipe were mechanically attached to the racking on both ends the discussion could be different.

Great. So what wire/cable type is typically used, and is it a type that requires raceway when 690.31(C) doesn't apply? If it does require a raceway outside the array, then that sleeve better be a raceway and meet all the raceway requirements, including fill.

Cheers, Wayne

 

[jaggedben]

Great. So what wire/cable type is typically used, and is it a type that requires raceway when 690.31(C) doesn't apply? If it does require a raceway outside the array, then that sleeve better be a raceway and meet all the raceway requirements, including fill.

Cheers, Wayne

That's one question, and I think the answer would be found in the product standard for PV wire or USE-2. I'm not entirely sure.

But the other question is whether there's any exception to fill and derating requirements, regardless of whether a 'raceway' or some other thing is either used or required. For example I think it's not really debatable that the conductors in the photo should be derated per 310.15(3)(B). Even if they were merely all ziptied together without the piece of metal.

 

[wwhitney]

That's one question, and I think the answer would be found in the product standard for PV wire or USE-2. I'm not entirely sure.

PV wire is not a Chapter 3 category, so its NEC use, beyond the allowance in 690.31(C), is limited to what other ratings the wire has, to my understanding. The one example I looked up is also rated RHW-2.

I don't believe Article 338 allows USE-2 single conductor cables to be run exposed above ground without a raceway. And RHH certainly can't be used that way in general. So that means that a raceway is required for the wires in the picture in the OP outside of "the PV array".

As such, the metal pipe in the picture is a raceway and is subject to fill limits and the conductors are subject to derating.

Now if the wires were some type that is allowed to be run exposed above ground, say UF cable, then I'd say the metal pipe in the picture is a sleeve and could be any material, not listed conduit. It still is obviously causing bundling for over 24", so derating would apply. But there would be no fill limits.

And no, beyond the allowances for nipples up to 24" in length, there's nothing in the NEC (*) that would relax the fill and derating requirements for conductors in conduit in that application. But you could put a box in the middle of the conduit run to take advantage of the 24" allowance on either side of it. Or just use a large box instead of conduit. Or check the allowances for wireways and/or cable trays.

Cheers, Wayne

(*) Not based on reading cover to cover but I think I've read all the possibly relevant sections, and no mention of it has ever come up here that I've seen in the last decade (and a half?)

 

[pv_n00b]

I think the question comes down to the wire type that is running through that piece of metal tube. If it's a wire type that can be run exposed without relying on the 690.31(C) allowances, then I agree with you it's a sleeve. If it's a wire type that is normally required to be run in a raceway, but 690.31(C) allows an exception to that ("within the PV array"), then whenever 690.31(C) doesn't apply, you need a raceway, and so the metal tube in the picture is the required raceway.

Cheers, Wayne

I agree. Which means, if the wire does not require a conduit where it is installed and I put it in a tubular sleeve-shaped object do I need to apply any of the requirements the NEC calls out for conduit?

 

[jaggedben]

Wayne pretty much got it right. The conductors in the photo are probably not allowed to be used in a building without a raceway outside of a PV array; that's definitely so if they are USE-2 and not PV wire.

Even if this was somehow not true, it's logically ridiculous that fill requirements should only apply when a raceway is required by code. The risk of damage to the conductors from pulling them through a too-tight space doesn't go away just because the raceway isn't required.

 

[LarryFine]

The risk of damage to the conductors from pulling them through a too-tight space doesn't go away just because the raceway isn't required.

Nor heat dissipation.

 

[jaggedben]

Nor heat dissipation.

Right, but the way 310.15(B)(3) is written, it applies regardless. Whereas the way 300.17 is written it seems to only apply within code defined 'raceways', which is illogical.

 

[pv_n00b]

Wayne pretty much got it right. The conductors in the photo are probably not allowed to be used in a building without a raceway outside of a PV array; that's definitely so if they are USE-2 and not PV wire.

Even if this was somehow not true, it's logically ridiculous that fill requirements should only apply when a raceway is required by code. The risk of damage to the conductors from pulling them through a too-tight space doesn't go away just because the raceway isn't required.

I agree that all the conduit considerations should not be ignored when using a sleeve. But I was just looking at it from the point of view of what the NEC says about it. And that's scant. Comes under the category of, just because I can do something does not mean I should do it.

 

[winnie]

I'd argue that a short length of tube enclosing conductors for physical protection has both less of an issue with conductor damage due to fill and less of an issue for derating/heat production.

First, one can easily line conductors up and slide them into a short enough length of tubing.

Second, a significant amount of heat will be conducted by the wires to the ends, where the wires spread out and can dissipate the heat to the air.

Not sure that this particular installation goes 'too far'; it is clearly longer than the 24" sleeve permitted if a conduit system is required, and it isn't clear that the conductors are permitted in the location of the sleeve without a conduit system. I just want to raise the point that the install as seen doesn't terribly bother me on the basis of either conduit fill nor derating.

Also: the conductors are quite spread out because of the connectors. Has the conduit fill actually been calculated? The results might be surprising.

-Jon

 

[jaggedben]

I'd argue that a short length of tube enclosing conductors for physical protection has both less of an issue with conductor damage due to fill and less of an issue for derating/heat production.

To a point, sure. But surely it can't be argued that the code contains a blanket allowance for any number conductors to be pulled through 'sleeves' to the point where damage is unavoidable.

 

[winnie]

To a point, sure. But surely it can't be argued that the code contains a blanket allowance for any number conductors to be pulled through 'sleeves' to the point where damage is unavoidable.

Agreed. Like I said, I can't say if this particular installation goes too far.

But I'd like to see a fill calculation. Look at the picture, the conduit looks packed, right? But if you assume #8 PV wire (0.292" diameter) in a 3" GRC, the fill limit is something like 42 conductors.

I think that having all of the connectors right near the end is spreading the conductors out, giving the illusion of an overfilled conduit.

Jon

 

[rainwater01]

I’ve never found a good answer to this question when researching online. Do bundled dc circuits react the same way as bundled ac circuits? Do they get less hot, more hot or are they the same?


Sent from my iPad using Tapatalk

 

[jaggedben]

I’ve never found a good answer to this question when researching online. Do bundled dc circuits react the same way as bundled ac circuits? Do they get less hot, more hot or are they the same?


Sent from my iPad using Tapatalk

The code treats them the same, and they essentially are. Heating is mostly a function of RMS current.