PV wires in the house - conduit question

[EPicTony]

I have 6 stings of #10 thhn entering my basement. The amperage is 11 amps/string. My EG4 inverters are about 50 lineal ft away from the basement entrance.
I'm thinking I should run the strings in pvc conduit to the inverters ? Am I on the right track ? I'm using 1.5" pvc conduit buried from the arrays (ground mounted) to the house.
Can I step down to a smaller diameter for the basement run ?
Thanks for any advise.

 

[MichaelK]

I also have six strings, but I placed my combiner box outside the utility room in a sheltered location. Then I have only one string coming out of the combiner, that penetrates the outer building wall though a standard service entrance like this. I use gray PVC conduit once it penetrates through the wall.

 

[Shimmy]

I believe the PV wires need to be in metal conduit indoors. What voltage? Do you have a disconnect where they enter?

 

[EPicTony]

I believe the PV wires need to be in metal conduit indoors. What voltage? Do you have a disconnect where they enter?

About 400vdc. I was putting an isolator at the array and dc breakers just before the inverters.

 

[EPicTony]

I also have six strings, but I placed my combiner box outside the utility room in a sheltered location. Then I have only one string coming out of the combiner, that penetrates the outer building wall though a standard service entrance like this. I use gray PVC conduit once it penetrates through the wall.
View attachment 113749

The 6 strings need to go to the inverters 2/strings to each inverter so I can't combine them like you did.

 

[x98myers7]

you need THWN or THHN-2 for underground, even in conduit. 90degC rated UL listed.

why are you running so many lines with such low amperage?

 

[stienman]

Most local jurisdictions require DC power wiring (such as from solar arrays and batteries) be in metal conduit inside buildings and dwellings. Check your local authority to confirm their code requirements.

For 11A, 10awg is overkill except over very, very long distances. 14awg can handle 15A and the power loses due to resistance will be lower than the cost difference between 14awg and 10awg by a wide margin - it would take decades for the power savings in lower resistance to pay for the cost difference.

 

[x98myers7]

Most local jurisdictions require DC power wiring (such as from solar arrays and batteries) be in metal conduit inside buildings and dwellings. Check your local authority to confirm their code requirements.

MC wire also is sufficient. the NEC ruled a few years back on this.

 

[MichaelK]

I believe the PV wires need to be in metal conduit indoors. What voltage? Do you have a disconnect where they enter?

Hummm, I did have an electrician inspect my system at initial completion, but that was not an issue that was brought up. Since is was plumbed in standard PVC conduit, or the fact that it only runs ~4' from the wall to the power center might be what makes a difference. There's a combiner to system breaker in the power center, so yes, there is a disconnect. It's 120VDC.

 

[Hedges]

Perhaps "MC" meaning "Metal Clad", not "MC" meaning "Multi-Contact" (which of course refers to connector, not wire and insulation.)

2020 National Electrical Code: Article 330 Metal-Clad Cable Type MC | JADE Learning

Metal-Clad (MC) Cable is used every day in the electrical industry. The true conduit benders hate it. The value engineering people love it. MC Cable is really a great product, has a wide variety of uses, and can be installed to look good

www.jadelearning.com

Wiring Methods for PV Systems and the NEC

Applying Code requirements correctly will help keep your photovoltaic (PV) installations safe and operating smoothly

www.ecmweb.com

"DC conductors in a building
Section 690.31(E), “Direct-Current Photovoltaic Source and Output Circuits Inside a Building,” was revised in the 2011 NEC. The 2008 language associated with this section was confusing and, in many cases, led to interpretations that included AC circuits. In 2011, the main language of this section was clarified, and four subsections were added to help further define the requirements associated with the DC conductors running in buildings.


The general rule states that the DC source and output circuits from a PV array shall be contained in metal raceways, MC cable that complies with 250.118(D), or metal enclosures from the first point of penetration to the first readily accessible disconnecting means. One of the clarifications addresses that this requirement is intended for the DC circuits only — not any AC circuits associated with the inverter’s output. The inclusion of MC cable was new to 2011, so be sure to make sure your AHJ is accepting that change if you plan to use this wiring method."

I think best to have PV DC wires inside EMC or IMC/Rigid. Metal conduit.

The question would be whether photovoltaic wire (what IS the proper name, if not "MC"?) can be used inside conduit. It is already water proof, but not intended for direct burial. It's extra thick insulation might mean in a cable, bundle, conduit it would need further derating. Normal use is in free air, which allows more cooling and higher ampacity.

 

[x98myers7]

Perhaps "MC" meaning "Metal Clad"

yep. MC is commonly known to be "metal clad"

https://www.solaredge.com/sites/default/files//dc_pv_output_circuits_inside_building.pdf

 

[EPicTony]

you need THWN or THHN-2 for underground, even in conduit. 90degC rated UL listed.

why are you running so many lines with such low amperage?

My solar panels are 450w each at 49voc and 11amps so I can only do 8 panels/string with EG4 inverters to stay under the max voc.
The array is 360 ft away so I used #10 to limit losses.

 

[EPicTony]

Most local jurisdictions require DC power wiring (such as from solar arrays and batteries) be in metal conduit inside buildings and dwellings. Check your local authority to confirm their code requirements.

For 11A, 10awg is overkill except over very, very long distances. 14awg can handle 15A and the power loses due to resistance will be lower than the cost difference between 14awg and 10awg by a wide margin - it would take decades for the power savings in lower resistance to pay for the cost difference.

The array is 360 ft away so I used #10 to limit losses.

 

[Hedges]

What Makes Photovoltaic Wire and Cable Different from Normal Cables? PV Wire vs. USE 2

With the recent increase in the use of solar panels, the sales of photovoltaic wire and cable skyrocketed. However, since solar cables are still a recent invention, they face a lot of misunderstandings. What are the unique characteristics of a photovoltaic cable? Why can you not just simply use...

nassaunationalcable.com

"You cannot use USE-2 in ungrounded photovoltaic arrays; this is the task that only PV wire can handle because service entrance cables can only be used in grounded systems."

If that refers not to ungrounded frames, but rather neither PV- nor PV+ being grounded, it would rule out USE-2 for many PV systems. Arrays used to be required to be grounded (but were often only grounded through a 1A fuse which would blow as part of GFCI function), but now many are ungrounded (all transformerless GT PV systems.)

"Both USE-2 and PV wire can be directly buried without the need for extra protection per NEC. However, some photovoltaic cables are not rated for direct burial, and it is best to check with the manufacturer before installing."

My first array I used UF between panels. Passed inspection, may not have been proper, but nothing wrong with it that I can think of.
Later panels came with PV wire and MC3 connectors, and I converted my first 24 panels to that.

 

[Ampster]

My solar panels are 450w each at 49voc and 11amps so I can only do 8 panels/string with EG4 inverters to stay under the max voc.

To clarify, you have a total of 48 panels in six strings of eight panels per string. The voltage per string is about 400 volts. Correct?

 

[EPicTony]

To clarify, you have a total of 48 panels in six strings of eight panels per string. The voltage per string is about 400 volts. Correct?

Yes 8x49v= 392v per string. Max on the EG4 is 450.

 

[Shimmy]

"You cannot use USE-2 in ungrounded photovoltaic arrays; this is the task that only PV wire can handle because service entrance cables can only be used in grounded systems."

USE-2 is specifically allowed, at least in the 2020 NEC (as is RHW-2).

 

[timselectric]

It will be grounded, when the shovel hits it. lol
Just make sure that you put the ground wire on top.

 

[niktak11]

Most local jurisdictions require DC power wiring (such as from solar arrays and batteries) be in metal conduit inside buildings and dwellings. Check your local authority to confirm their code requirements.

For 11A, 10awg is overkill except over very, very long distances. 14awg can handle 15A and the power loses due to resistance will be lower than the cost difference between 14awg and 10awg by a wide margin - it would take decades for the power savings in lower resistance to pay for the cost difference.

I wouldn't really call it overkill considering you need to derate by 50% with that conduit fill

 

[Hedges]

Yeah, but that is 50% from the 40A ampacity of 10 awg, leaving 20A allowed. (unless ampacity of PV wire is different.)
For 12 awg (which my strings use), 50% of 30A is 15A. I'm pushing toward > 31 wires, 40% of ampacity allowed.

15A / 1.56 = 9.6A, so 12 awg would not be compliant for his 11A panels. 10 awg was required.