Bundling pv conductors

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panhandle444

Member
Location
oklahoma
What's the proper way to bundle pv homeruns under an array? Keep each positive and negative together if possible? Is derating the same for DC as with AC? Thanks
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
No derating except for temperature is required for conductors that are not run in a raceway. You use the same tables and calcs as with AC. Positive and negative need to be brought to the same raceway or junction box where they leave the array.

Otherwise he more organized you can keep it the better, but there is no 'proper' way. On simple arrays I always just brought the home runs straight up to the top rail and then bundled them all together along that rail toward the j-box. (Same with the ground wire.) Identification of both ends before you cut the wire is essential to being efficient.
 

Carultch

Senior Member
Location
Massachusetts
What's the proper way to bundle pv homeruns under an array? Keep each positive and negative together if possible? Is derating the same for DC as with AC? Thanks

It is best to keep associated positives and negatives together for as long as possible, to keep the magnetic field from propagating and to limit the influence of lightning induced fields. Obviously you will have to separate at one point to branch off to each side.

By default, I'd assume that derating practices should apply just as they do for all other circuits. Given open air, they technically are not conductors in a raceway and should therefore have slightly greater ampacity, but there isn't a code model for how to do it a different way.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Is that exclusive to PV circuits? Because that is not the case with standard circuits.

(This was so similar I posted my response to the wrong comment...)

My mistake. But it's never arisen as an issue for me. Considering that one could use the free-in-air table, and that one will have already sized wire-gauge in the raceway for any derate, you'd pretty much never have a higher derate on the array than in the homerun in a raceway.
 

Carultch

Senior Member
Location
Massachusetts
(This was so similar I posted my response to the wrong comment...)

My mistake. But it's never arisen as an issue for me. Considering that one could use the free-in-air table, and that one will have already sized wire-gauge in the raceway for any derate, you'd pretty much never have a higher derate on the array than in the homerun in a raceway.

Are you permitted to use the free air table for wires clipped to a racking system or in a cable tray? The NEC doesn't specify how to adjust ampacity for listed PV wire of sizes such as #10 in a cable tray.
 

iwire

Moderator
Staff member
Location
Massachusetts
If there is nothing in 690 changing things the normal rules of derating apply.

If they are bundled they are not free air conductors
 

Carultch

Senior Member
Location
Massachusetts
If there is nothing in 690 changing things the normal rules of derating apply.

If they are bundled they are not free air conductors

So if I have just one conductor clipped to a rack, it counts as a free air conductor? But the instant I bundle a second one with it, it now has to have the ampacity from 310.15(B)(16)?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
So if I have just one conductor clipped to a rack, it counts as a free air conductor? But the instant I bundle a second one with it, it now has to have the ampacity from 310.15(B)(16)?

And define bundled. What if they are tied or clipped flat against the rail? Is there somewhere that defines the required spacing? What if they are bundled every 48" but they sag apart in between?

Yeah, I have a bit of a problem with applying a derating for this. If only because clearly this particular question was never considered when making these code sections.
 

iwire

Moderator
Staff member
Location
Massachusetts
Yeah, I have a bit of a problem with applying a derating for this. If only because clearly this particular question was never considered when making these code sections.

You always seem to think PV is something so different. :)

The question is always 'what is bundling' well that is going to be up to the AHJ based on this

(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a
Raceway or Cable. Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are installed
without maintaining spacing for a continuous length longer
than 600 mm (24 in.) and are not installed in raceways,
the
allowable ampacity of each conductor shall be reduced as
shown in Table 310.15(B)(3)(a). Each current-carrying conductor
of a paralleled set of conductors shall be counted as
a current-carrying conductor.


Where conductors of different systems, as provided in
300.3, are installed in a common raceway or cable, the
adjustment factors shown in Table 310.15(B)(3)(a) shall
apply only to the number of power and lighting conductors
(Articles 210, 215, 220, and 230).
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Iwire, can you give an example of another similar type of installation where a derate for bundled conductors is traditionally applied?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Are you permitted to use the free air table for wires clipped to a racking system or in a cable tray? The NEC doesn't specify how to adjust ampacity for listed PV wire of sizes such as #10 in a cable tray.
For PV source circuits most designers use #10; the ampacity of #10 is so much higher than Isc for a string that this is seldom an issue.
 

SolarPro

Senior Member
Location
Austin, TX
To be fair, Jaggedben is usually on the right side of the law. Just not in this case. Bundled cables are subject to ampacity reductions.

@ggunn is right, 10AWG source circuit conductors likely have the required ampacity even after factoring in the conditions of use.
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
To be fair, Jaggedben is usually on the right side of the law. Just not in this case. Bundled cables are subject to ampacity reductions.

@ggunn is right, 10AWG source circuit conductors likely have the required ampacity even after factoring in the conditions of use.
It's important only in the calculations if the designer shows his (or her) work. I usually do but I often wonder if anyone but me even looks at that stuff. :D
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
To be fair, Jaggedben is usually on the right side of the law. Just not in this case. Bundled cables are subject to ampacity reductions.

I'm not questioning what the code says, although I was unaware of that particular passage before this thread. But I'm questioning what constitutes bundling and not maintaining spacing.

For example, if I use this clip to attached 4 current carrying PV wire conductors to a rail, do I have to derate? Is that bundling or not?

Also, for PV wire tied or clipped to panels and rails, can I not apply the derate to the table for free-in-air conductors instead of the one for conductors in a raceway or cable?

Bottom line is I have never had an AHJ raise this issue and in pretty much all the systems I install it would make no difference.
 

SolarPro

Senior Member
Location
Austin, TX
This is an interesting question if only because the proper treatment will depend on what installers do in the field. On the one hand, they could route source circuit conductors such that no or minimal ampacity adjustment is required. On the other hand, they could do something like this which clearly requires an ampacity adjustment:
 

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Carultch

Senior Member
Location
Massachusetts
For PV source circuits most designers use #10; the ampacity of #10 is so much higher than Isc for a string that this is seldom an issue.

Until you've got 50 of them in a cable tray. If the Massachusetts Electric Code applies, it is isn't a problem. But if the NEC applies, that is 14A, which is lower than the fuse.

And it isn't a trivial task to simply upsize to #8, because connectors for #8 are much less common.
 
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