Conductor Sizing and OCP for a AC Solar Panel

[elmundogrande]

I went to 690.6(B) inverter output then I went to 690.8(A)(3) found inverter output to be continuous then I went to 690.8(B) that states all photovoltaic systems shall be continuous and require the 125% to the output amperage. I was told that no 690.8 does not apply to AC Solar Panels that 690.6 does and go to 690.6(E) that sends you to 240.5(B)(2) and that 125% is not needed, need help who is right.

 

[Smart $]

I went to 690.6(B) inverter output then I went to 690.8(A)(3) found inverter output to be continuous then I went to 690.8(B) that states all photovoltaic systems shall be continuous and require the 125% to the output amperage. I was told that no 690.8 does not apply to AC Solar Panels that 690.6 does and go to 690.6(E) that sends you to 240.5(B)(2) and that 125% is not needed, need help who is right.

I am. :happyyes:

...but you are, too!

690.6 applies only to AC Modules, which are inverters, and their output is specified such in 690.6(B). 690.6(E) only applies to the use of fixture wire, i.e. the wiring between branch circuit conductor and a single module. It does not apply to any aggregation on the utilization side of the fixture wire tap.

 

[jaggedben]

I was told that no 690.8 does not apply to AC Solar Panels...

That's not really correct. 690.6 exempts AC modules only from requirements regarding source circuits and inverters. 690.8 still applies regarding inverter outputs. The conductors and OCP must be sized to 125% of the total nameplate output of the modules.

Usually with micro-inverters and AC modules the manufacturer specifies a max OCPD rating that you cannot exceed. Your conductors can be sized to be protected by that OCP according to Art 240, or be larger to mitigate voltage rise. It's typical practice in the industry to use minimum #10 wire for micros and AC modules, to account for voltage rise, even if it's not required for overcurrent protection. With longer runs to the point of interconnection you may need larger conductors. Sizing conductors only for the requirements of 690.8 is likely to lead to modules tripping off due to AC-voltage-out-of-range errors unless you have very short wiring distances.

 

[elmundogrande]

just my thoughts ac panels

just my thoughts ac panels

This Electrical Engineer is say that you can put 10 panel in parallel with a maximum output current on 1.8amps on a 20 amp breaker because 240.5(B)(2) let's him, I said no you can't do that 690.6(B) the output current of a AC module shall be the inverter output current that sends you to 690.8(A)(3) then to 690.8(B) and 690.8(B)(1)

 

[jaggedben]

You are correct. The max inverter output amps that can be put on a 20A branch circuit is 16A. As Smart$ explained, the applicability of 240.5(B)(2) is only to the output wiring of the individual AC modules, and perhaps at most the manufacturer-supplied wiring harness between modules. I don't see how it can be applied to the branch circuit wiring between the array and the interconnection point.

Furthermore, if you try to use 18 or 16 gauge wiring for a branch circuit up to 50 or 100ft, respectively, you are pretty much guaranteed to have voltage problems. So even if the engineer stretches his interpretation of the code to allow it, your solar system probably won't function.

 

[jaggedben]

Another thing is that 240.5(B)(2) doesn't say anything about how many amps of solar you can put on certain size breaker. It refers to wire size only.

 

[Smart $]

This Electrical Engineer is say that you can put 10 panel in parallel with a maximum output current on 1.8amps on a 20 amp breaker because 240.5(B)(2) let's him, I said no you can't do that 690.6(B) the output current of a AC module shall be the inverter output current that sends you to 690.8(A)(3) then to 690.8(B) and 690.8(B)(1)

You are correct.

240.5(B)(2) is about using a smaller "fixture wire" than is otherwise permitted for branch circuit wiring [e.g. 240.4(D)].

Another point is that in order to comply with 240.5(B)(2) the fixture wires must be of a type listed in Table 402.3, and comply with the remainder of Article 402.

I'd say the best approach to use in this situation would be to discuss this with the AHJ. If the AHJ agrees, have the EE contact the AHJ directly, and tell the EE you are just trying to save him a backcharge for correcting it later.

 

[elmundogrande]

the engineers response

the engineers response

Mike Holt?s website doesn?t delve into AC Modules .. nor do I believe everything I read on the web.

The NFPA 70, NEC Section 690 is AC-Module specific. 690.6(E) directly addresses concerns related to conductor sizing and OCP device ratings for AC Modules, and is used as a citation in my White Paper.

You?re welcome to disagree, but we?ve got countless jurisdictions all over the country that have read 690, and the White Paper in particular, and have formed an opinion that differs from yours. Jeff may encounter an obstiate and highly opinionated AHJ .. in which case all bets are off.

YMMV.

Dan
This was his response when I told him about this tread I have a copy of the white papers and still disagree he is a engineer and I am a Electrician/contractor/Instructor in the field so I would have to go with my teachings in

 

[ggunn]

Mike Holt?s website doesn?t delve into AC Modules .. nor do I believe everything I read on the web.

The NFPA 70, NEC Section 690 is AC-Module specific. 690.6(E) directly addresses concerns related to conductor sizing and OCP device ratings for AC Modules, and is used as a citation in my White Paper.

You?re welcome to disagree, but we?ve got countless jurisdictions all over the country that have read 690, and the White Paper in particular, and have formed an opinion that differs from yours. Jeff may encounter an obstiate and highly opinionated AHJ .. in which case all bets are off.

YMMV.

Dan
This was his response when I told him about this tread I have a copy of the white papers and still disagree he is a engineer and I am a Electrician/contractor/Instructor in the field so I would have to go with my teachings in

If you don't quote the posting to which you are disagreeing, it's difficult to ascertain what point you are trying to make.

 

[Smart $]

Mike Holt’s website doesn’t delve into AC Modules .. nor do I believe everything I read on the web.

The NFPA 70, NEC Section 690 is AC-Module specific. 690.6(E) directly addresses concerns related to conductor sizing and OCP device ratings for AC Modules, and is used as a citation in my White Paper.

You’re welcome to disagree, but we’ve got countless jurisdictions all over the country that have read 690, and the White Paper in particular, and have formed an opinion that differs from yours. Jeff may encounter an obstiate and highly opinionated AHJ .. in which case all bets are off.

YMMV.

Dan
This was his response when I told him about this tread I have a copy of the white papers and still disagree he is a engineer and I am a Electrician/contractor/Instructor in the field so I would have to go with my teachings in

What is the make and model of AC Module package? The only instance where I could see the EE being correct is if the entire package (i.e. all 10 modules and associated interconnect cables) is listed to be on a 20A branch circuit...

PS: Being an EE, publishing a white paper which is accepted as authoritative by AHJ's all over the country, is no ascertation of correctness or compliance.

 

[ggunn]

Mike Holt?s website doesn?t delve into AC Modules .. nor do I believe everything I read on the web.

The NFPA 70, NEC Section 690 is AC-Module specific. 690.6(E) directly addresses concerns related to conductor sizing and OCP device ratings for AC Modules, and is used as a citation in my White Paper.

You?re welcome to disagree, but we?ve got countless jurisdictions all over the country that have read 690, and the White Paper in particular, and have formed an opinion that differs from yours. Jeff may encounter an obstiate and highly opinionated AHJ .. in which case all bets are off.

YMMV.

Dan
This was his response when I told him about this tread I have a copy of the white papers and still disagree he is a engineer and I am a Electrician/contractor/Instructor in the field so I would have to go with my teachings in

Looking at your OP, I can tell you that the most that you can put on a 20A backfed breaker is 16A of total maximum inverter output current, no matter where it comes from.

Also, 690.6(E), which points to 240.5(B)(2) and says nothing about OCP other than to relate a minimum fixture wire size to an OCP rating, assumes that each AC module individually connects to the branch circuit, which is not the way that an Enphase array connects.

 

[elmundogrande]

ac panels

ac panels

exeltechsolar.com

 

[Smart $]

exeltechsolar.com

That's the manufacturer of the AC Module, and I believe their documentation isn't valid for installation purposes because the module is incorporated with the PV panel by other maunufacturers. Now if the package manufacturer includes that documentation in their listing and instructions, it could be allowed. That's why I asked for make and model of the package.

I can tell from the White Paper on their website that they don't know how to apply OCP and conductor sizing rules. For example, there is no mention of terminal temperature limitations imposed by 110.14(C) (possibly 60?C, at best 75?C), and they justify OCPD rating from the derated ampacity of the conductor.

IMO, the manufacturer would have furnish everything, including the OCPD, as a listed package for it to be truly compliant under the NEC.

Ohhh! and as I mentioned earlier that 240.5(B)(2) applies to "fixture wire" and the wire type must be listed in Table 402.3. The White Paper says the home-run cable conductors are XHHW-2... and that is not a type listed in Table 402.3!!!

 

[jaggedben]

IMO, the manufacturer would have furnish everything, including the OCPD, as a listed package for it to be truly compliant under the NEC.

Totally agree. And the NEC is actually very precise and clear about this (which isn't always the case ) .

Namely, it would have meet the requirement in 690.8(B)(1) unless it meets the exception. The exception specifically calls out "an assembly, together with it's overcurrent device(s), that is listed for continuous operation at 100 percent of it's rating..." (Emphasis mine.)

The same thing is repeated in 705.60(B) with the same exception with the same wording.

The white paper just conveniently fails to mention these code sections. Gosh, if I could have ignored those sections whenever I wanted to I probably could have avoided a few line-side taps and service upgrades for the companies I've worked for .

 

[tallgirl]

The ACPV module or microinverter should be UL / CSA / e-i-e-i-o listed and you should follow the listing information. The only vendor I'm aware of that doesn't have some sort of integrated / vendor-provided cabling is ExcelTech, and I believe their approach is insulation displacement connectors into a piece of 10/2 UF.

Show the engineer(s) and / or AHJs the listing information.

 

[jaggedben]

The ACPV module or microinverter should be UL / CSA / e-i-e-i-o listed and you should follow the listing information. The only vendor I'm aware of that doesn't have some sort of integrated / vendor-provided cabling is ExcelTech, and I believe their approach is insulation displacement connectors into a piece of 10/2 UF.

Show the engineer(s) and / or AHJs the listing information.

But you would agree that (unless it's an assembly with OCP that meets the exception), you still can't put more than 80% of the OCP rating on a branch circuit, right?

 

[Smart $]

exeltechsolar.com

FWIW, here's another item of non-compliance from my perspective...

The White Paper gives the following description of their Home Run Cable:

Exeltech’s AC Module Home Run cable consists of three 12AWG PVC-insulated copper conductors contained in and protected by an outer jacket of cross-linked polyethylene (XLPE). This cable is certified to UL Standard 1277 and UL Standard 1681 under Underwriters Laboratories file number E171058. It is qualified as XHHW-2, 90?C wet or dry, sunlight resistant, 12 AWG copper x 3, double-jacketed, flame-retardant, moisture resistant, and certified to 600 Vac. This cable is suitable for direct burial in wet or dry locations.

A file number search on UL.com yields the following:

QPOR.E171058
Power and Control Tray Cable​

---

Power and Control Tray Cable​

TELEDYNE STORM PRODUCTS INC	E171058
9215 PREMIER ROW
DALLAS, TX 75247 USA

http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073992361&sequence=1

See 336.10 and 336.12 for uses permitted and not of Type TC cable... but I'm pretty certain the installation of the OP is a "not".

Additionally, it says the cable is rated XHHW-2. AFAIK, cables are not rated XHHW-2, only conductors are... and it says the conductors are PVC insulated, which means they can't be XHHW-2.


Seems to me whomever authored the white paper is, shall we say, out of their league.

 

[elmundogrande]

ac panels

ac panels

The panels are Helios AC Modules 6T series Max output current is 1.8 amps max string of 10 panels on a 20A ocpd 18x125%=22 my math

 

[jaggedben]

18x125%=22 my math

Yeah, I think we all agree with your math. :happyyes: So do Enphase (17 inverters * .9A * 1.25 = 19.125) and SolarBridge (16 * .99 * 1.25 = 19.8) and Enecsys (17 * .94 * 1.25 = 19.975).

Maybe someone should tell all these companies that Exeltech has 'discovered' that they are choosing limits that are too low. I mean, I'd love to save our customers the cost of a subpanel on a 20 panel Enphase system.

 

[Smart $]

The panels are Helios AC Modules 6T series Max output current is 1.8 amps max string of 10 panels on a 20A ocpd 18x125%=22 my math

Helios' website and downloadable literature provide no additional information to indicate 100% NEC compliance.