Question on pv wiring

[Jpflex]

I have noticed that safety training for my new job focuses on NFPA 70E rather than NEC. I do see some contradictions or conflicts between the two.

In NEC 690.31 A 2 it is stated that where wires are not guarded and operating at voltages GREATER THAN 30 volts that are readily accessible to unqualified persons, shall be installed in type mc cable, multi conductor cable or in a raceway.

However, our job is safety training employees according to OSHA and NFPA which says that exposed wires accessible to unqualified personnel must be guarded with such raceways or barriers if voltages are at 50 volts or more as opposed to NEC at 30 volts?

I understand it’s wise to follow company policy but it appears some NFPA rules may pose a violation to NEC rules which also must be followed, so what do you do?




Also, the other topic regards NEC 690.31 A 3 for conductors ampacity rated at 105 and 125 degrees celcius to use table 690.31 A31

Does this section mean that the insulation for these pv wires are rated for the ampacity shown on this table for those temperatures and if so how could you use or size these wires for typical terminations for equipment limited to the 60 or 75 degree celcius?

 

[tortuga]

I have noticed that safety training for my new job focuses on NFPA 70E rather than NEC. I do see some contradictions or conflicts between the two.

In NEC 690.31 A 2 it is stated that where wires are not guarded and operating at voltages GREATER THAN 30 volts that are readily accessible to unqualified persons, shall be installed in type mc cable, multi conductor cable or in a raceway.

I don't see a conflict there, if its not a solar system then 50 volts or more, if you in a situation where 690.31 applies then 690 in the NEC prevails and the floor limit is 30 volts.

 

[tortuga]

That being said I have no idea where some of the solar and energy storage limits originate from or if they are based on any real data.
Telco's have used 48 volts since the telegraph days with out needing raceway, thats where the 50 volt floor comes from.
120VDC was the service voltage to residences from the Edison DC system for many decades before AC took over and article 210 still allows using 120 VDC in a dwelling to this day, but in 706.20(B) energy storage systems are limited to a lower voltage like 100V for some unknown reason.

 

[Jpflex]

That being said I have no idea where some of the solar and energy storage limits originate from or if they are based on any real data.
Telco's have used 48 volts since the telegraph days with out needing raceway, thats where the 50 volt floor comes from.
120VDC was the service voltage to residences from the Edison DC system for many decades before AC took over and article 210 still allows using 120 VDC in a dwelling to this day, but in 706.20(B) energy storage systems are limited to a lower voltage like 100V for some unknown reason.

But how do you use pv wires with such high temperature rated insulation above 100 degrees celcius? Do you terminate on bussbars and extend with wiring rated 60 to 75 degrees celcius for equipment termination or how would you find the wires ampacity for 60 and 75 degrees celcius with the NEC tables shown?

 

[ggunn]

But how do you use pv wires with such high temperature rated insulation above 100 degrees celcius? Do you terminate on bussbars and extend with wiring rated 60 to 75 degrees celcius for equipment termination or how would you find the wires ampacity for 60 and 75 degrees celcius with the NEC tables shown?

You simply size the wiring as if it were 75 degree rated irrespective of its actual rating.

 

[wwhitney]

But how do you use pv wires with such high temperature rated insulation above 100 degrees celcius?

Seems like the primary use would be as a higher starting ampacity when derating for ambient temperature and number of CCCs.

But if the final ampacity after doing that is significantly higher than the 75C termination (non-derated) ampacity, you'd have the option to run the conductor to a junction box near the equipment and use a 90C or 105C splicing method to larger conductors for the run from the junction box to the equipment. Not sure if it's done in practice or is just a theoretical option.

Cheers, Wayne

 

[Jpflex]

you'd have the option to run the conductor to a junction box near the equipment and use a 90C or 105C splicing method to larger conductors for the run from the junction box to the equipment. Not sure if it's done in practice or is just a theoretical option.

Cheers, Wayne

Mike holt had a video on this but a buss at a junction box was used to junction the 90 degree wire and 75 degree wire at opposite ends of a buss strip. Would busses normally by rated for 90 to 105 degree celcius termination?

Would there be an option to find the 60 and 75 degree ampacity of this pv wire or does this not apply?

 

[Jpflex]

You simply size the wiring as if it were 75 degree rated irrespective of its actual rating.

Based on what table or column or type of wire. The NEC table for this column does not have a 75 or 60 degree ampacity rating

 

[wwhitney]

Based on what table or column or type of wire. The NEC table for this column does not have a 75 or 60 degree ampacity rating

Table 310.16. Table 690.31(A)(b) just gives the 105C and 125C columns that are missing from Table 310.16.

Cheers, Wayne

 

[tortuga]

Based on what table or column or type of wire. The NEC table for this column does not have a 75 or 60 degree ampacity rating

You'd have to look at the sticker on the spool of wire and see if its dual listed as a type of insulation in table 310.4
I have seen PV wire that is XLPE and RHW-2. Then you can use that wire for a non-pv application as RHW-2.
EPDM is also used as motor lead wire by motor shops I have not seen it dual listed but it might be.

 

[wwhitney]

You'd have to look at the sticker on the spool of wire and see if its dual listed as a type of insulation in table 310.4

PV wire doesn't have to be dual-listed. (2020) NEC 690.31(C)(1) provides permission to use it in "exposed outdoor locations in PV system dc circuits within the PV array." So if it is so used, and if it terminates at equipment with a 60C, 75C, or 90C termination temperature limit, then you'd just use the appropriate column of Table 310.16 for the termination ampacity check.

I agree that if PV wire is dual-listed, and if the conductor passes from a region where its use is allowed under 690.31(C) to a region where its use is not so allowed, then in the latter region you'd need to rely on its second listing. You'd do two separate ampacity calculations, one for the 690.31(C) region where the 105C or 125C ampacity may be utilized (assuming it is so marked), and one for the other region, when you'd be limited to the Table 310.16 values, based on its second listing.

Cheers, Wayne

 

[wwhitney]

Hmm, UL 4703 "Photovoltaic Wire" only recognizes a 90C wet rating, along with a dry rating of 90C, 105C, 125C, or 150C.

So it seems like the utility of the 105C or 125C rating would be very limited, you'd need a location for which the use of PV wire is allowed under 690.31(C), which means outdoors, but it would need to be a dry location. And if the wire also runs out under the array, the wire would be limited to the 90C wet location ampacity (on the assumption that under the array is always a wet location).

But I guess you might be able to create an outdoor dry location where a bunch of wires from different array segments come together, and then use the 105C or 125C dry location rating to help with the increased number of CCCs in that dry location confluence.

My comments are all theoretical; is the 105C or 125C dry location rating of PV wire of any use in practice?

Cheers, Wayne

 

[tortuga]

Hmm, UL 4703 "Photovoltaic Wire" only recognizes a 90C wet rating, along with a dry rating of 90C, 105C, 125C, or 150C.

So it seems like the utility of the 105C or 125C rating would be very limited, you'd need a location for which the use of PV wire is allowed under 690.31(C), which means outdoors, but it would need to be a dry location. And if the wire also runs out under the array, the wire would be limited to the 90C wet location ampacity (on the assumption that under the array is always a wet location).

But I guess you might be able to create an outdoor dry location where a bunch of wires from different array segments come together, and then use the 105C or 125C dry location rating to help with the increased number of CCCs in that dry location confluence.

My comments are all theoretical; is the 105C or 125C dry location rating of PV wire of any use in practice?

Cheers, Wayne

The PV wire I have seen in practice also has a RHW-2 listing, which is handy for stuff other than PV like if you had a 2000V feeder.