Is conduit required in attic for microinverter system? And lots of other code Q's.

[giskard]

Hello all,

I'll be installing a small semi DIY system (with the help of a pro) in San Jose, CA, using 6 panels and Enphase M215 micro-inverters. The plan is to penetrate the roof under or near the last panel and route the (AC) circuit through the attic. No conduit on the roof. The panels will be on the opposite side of the house from the service entrance. I do power electronics design for a living so I'm no stranger to ohms law and high voltages lol.

The house was built in the late 60s and some of the existing circuits going from the service panel into the attic don't have conduit, but one of them has flexible conduit. The installer guy commented that the city inspector may flag the flexible conduit and require me to rip it out before approving the solar system. He also said that solid conduit is required for the solar branch circuit in the attic.

1) In general (not solar), why is no-conduit OK for some circuits, but flex conduit not OK? It makes no sense to me that either no conduit, or solid conduit, are OK but flex conduit is not OK.

2) Is conduit required for micro-inverter AC output in the attic? Installer says yes. The 6 panels will only put out about 5.5A. I don't understand why 15A lighting branch circuits don't require conduit but micro-inverter outputs would. The micro-inverters will not put out any voltage if they do not sense the presence of the mains. If the breaker feeding it is opened, the micro-inverters will shut down.

3) Installer guy says 10 AWG cable is required, with 8 AWG ground. Why would 10 AWG be required for a circuit that produces < 6A, but 14 AWG is OK for 15A lighting branch circuits?

4) The Enphase M215's are the "IG" (integrated ground) variant, which means they have double insulation internally and do not require a ground connection for Safety to prevent electric shock in the case of internal insulation failure. (Like how some home electronic appliances and laptop chargers have a plug that don't have the third, ground prong). So AFAIK that means only the panel bracketry has to be grounded. Given that the panels themselves are electrically isolated from the mains with double insulation inside the inverter, the only ground needed would be the frame, for lightning protection, like a satellite dish. Therefore (a) the AWG 8 ground wire isn't technically needed (it's like running an extension to a power supply that has no 3rd ground prong, so the extension only needs 2 wires), and, the best way to ground the frame for lightning protection is to drop a wire straight down from the panels along the nearest side of the house into a ground rod or water pipe. (the panels are on the opposite side of the house from the service entrance) However, installer guy says code says it should be grounded all the way back to the service entrance. To me this seems less safe than a shorter connection to a ground rod, for lightning protection.

5) My existing ground rod at the service entrance is 1/2". Installer seems to imply I need to drive in a new 5/8" rod to bring it up to present code. Is this correct?

6) I would like to verify that I can simply connect the solar system via a pair of 240V breakers, and there is no need for a sub panel (a requirement for that would make no sense).

Thanks all.

[inetdog]

6) I would like to verify that I can simply connect the solar system via a pair of 240V breakers, and there is no need for a sub panel (a requirement for that would make no sense).

Thanks all.

Depends on the NEC cycle (year) that applies to you.
As of [2014] the final point of interconnection of the PV system to the wiring system must be a single breaker or disconnect switch.
Before that, you could use two or more breakers in the main panel as long as you also meet the 120% rule and place all of the PV breakers grouped together at the opposite end of the panel bus from the main.

[giskard]

Depends on the NEC cycle (year) that applies to you.
As of [2014] the final point of interconnection of the PV system to the wiring system must be a single breaker or disconnect switch.
Before that, you could use two or more breakers in the main panel as long as you also meet the 120% rule and place all of the PV breakers grouped together at the opposite end of the panel bus from the main.

What determines which NEC cycle applies to me?
TIA

[foo1bar]

What determines which NEC cycle applies to me?
TIA

Local law.

I believe San Jose, CA would currently be using 2013 California Electrical Code which is based on NEC 2011

https://www.mikeholt.com/necadoptionlist.php

[foo1bar]

5) My existing ground rod at the service entrance is 1/2". Installer seems to imply I need to drive in a new 5/8" rod to bring it up to present code. Is this correct?

I don't know - but it's cheap enough to do that if the building dept. wants it, it's not worth arguing.
5/8 rod is $12; clamp and wire will be a few bucks. An hour with a small sledge hammer to pound it down into the soil, and you're done.

[giskard]

Thanks.

Depends on the NEC cycle (year) that applies to you.
As of [2014] the final point of interconnection of the PV system to the wiring system must be a single breaker or disconnect switch.
Before that, you could use two or more breakers in the main panel as long as you also meet the 120% rule and place all of the PV breakers grouped together at the opposite end of the panel bus from the main.

Does this mean that the (2) solar breakers need to be at the bottom left, because my mains are at the top left?

120% rule means the breakers' rating need to be >=120% of the max current?

[sdold]

Article 690 (solar) and 705 (adding another power generation source) in the NEC or CEC are where you can find that info.

[Mike90250]

I don't know - but it's cheap enough to do that if the building dept. wants it, it's not worth arguing.
5/8 rod is $12; clamp and wire will be a few bucks. An hour with a small sledge hammer to pound it down into the soil, and you're done.

I love it when a ground rod gets 3' down, hits a rock, and pretzels under the surface.

[inetdog]

Thanks.



Does this mean that the (2) solar breakers need to be at the bottom left, because my mains are at the top left?

120% rule means the breakers' rating need to be >=120% of the max current?

If the main is at the top (either right or left, since the breakers in both columns typically connect to the same common bus bars) then the PV backfeed need to be at the bottom. Preferably one on the right and one on the left.
The goal is to eliminate the possibility of load breakers being installed between the main and the PV breakers in electrical sense. That means that you really need to know how the bus bars run and how the breakers connect to them.

The 120% rule does not involve load breakers at all, and states that the sum of the main and total PV must not exceed 120% of the bus bar rating.
In some panels the bus rating is greater than that of the pre-installed main breaker, such as a 100A main panel having a 125A rated bus.

[JFinch57]

1) In general (not solar), why is no-conduit OK for some circuits, but flex conduit not OK? It makes no sense to me that either no conduit, or solid conduit, are OK but flex conduit is not OK.

2) Is conduit required for micro-inverter AC output in the attic? Installer says yes. The 6 panels will only put out about 5.5A. I don't understand why 15A lighting branch circuits don't require conduit but micro-inverter outputs would. The micro-inverters will not put out any voltage if they do not sense the presence of the mains. If the breaker feeding it is opened, the micro-inverters will shut down.

3) Installer guy says 10 AWG cable is required, with 8 AWG ground. Why would 10 AWG be required for a circuit that produces < 6A, but 14 AWG is OK for 15A lighting branch circuits?

4) The Enphase M215's are the "IG" (integrated ground) variant, which means they have double insulation internally and do not require a ground connection for Safety to prevent electric shock in the case of internal insulation failure. (Like how some home electronic appliances and laptop chargers have a plug that don't have the third, ground prong). So AFAIK that means only the panel bracketry has to be grounded. Given that the panels themselves are electrically isolated from the mains with double insulation inside the inverter, the only ground needed would be the frame, for lightning protection, like a satellite dish. Therefore (a) the AWG 8 ground wire isn't technically needed (it's like running an extension to a power supply that has no 3rd ground prong, so the extension only needs 2 wires), and, the best way to ground the frame for lightning protection is to drop a wire straight down from the panels along the nearest side of the house into a ground rod or water pipe. (the panels are on the opposite side of the house from the service entrance) However, installer guy says code says it should be grounded all the way back to the service entrance. To me this seems less safe than a shorter connection to a ground rod, for lightning protection.

5) My existing ground rod at the service entrance is 1/2". Installer seems to imply I need to drive in a new 5/8" rod to bring it up to present code. Is this correct?

6) I would like to verify that I can simply connect the solar system via a pair of 240V breakers, and there is no need for a sub panel (a requirement for that would make no sense).

Thanks all.

1/2. When you say "flex conduit" are you referring to MC cable? I'm an engineer, not an electrician, but don't know of any requirement to run conduit inside of your house no matter what it's connected to. Personally, inside I would use 90 degree C MC cable and connect in your attic to watertight conduit leading to a junction box on your roof.

3. Solar is rated at continuous and the ambient temperature (high in attic) and voltage drop over a distance plays into the calculation. I ran it on http://www.electrician2.com/calculat...cpd_ver_1.html and it doesn't go to #10 until a 17A load, even at high temperature using 75 deg termination. Maybe he's allowing for future expansion? Personally, I run #10 on all of my Enphase strings, but I usually have them maxed out.

4. For the generation #4 Enphase inverters I would think that you don't need a larger ground than the feed circuit. You might want to contact Enphase support or send an email to Mike Holt. Mike usually is quick to respond, although his replies can be lengthy! Grounding the array for lightning protection is a good idea with a piece of bare braided copper all the way down the outside of you house to a dedicated ground rod. They sell special wire for this.

5. If you have a single ground rod the new code is to have 2 rods, separated by at least 5' (I think, or maybe 6'?). The inspector will want to see this and it's a good idea, helps to kill stray voltage coming in on your neutral wire.

6. Yes, for that small load connecting to a single 2 pole breaker is the way to do it, not a pair of 240V breakers!

[foo1bar]

1/2. When you say "flex conduit" are you referring to MC cable? I'm an engineer, not an electrician, but don't know of any requirement to run conduit inside of your house no matter what it's connected to.

PV DC wires require metal conduit inside the building. (MC might satisfy that requirement - I'd have to look that up)
wires from enphase microinverters? I don't know. (enphase probably has a FAQ about that)

6. Yes, for that small load connecting to a single 2 pole breaker is the way to do it, not a pair of 240V breakers!

I think he's planning on a pair of 240V breakers - that he has multiple "strings" of enphase coming in, and needs multiple breakers to support them.
I don't know enphase or how many microinverters/strings he's doing - so I'm not sure if multiple 240V breakers is required or if he can do just one.
My advice is to follow the manuf. directions.
And if their directions aren't clear (or aren't exactly like what you're doing) then I'd get someone knowledgable to look at the plans.

[sdold]

I bet he means a single double pole breaker. Probably a 20A or 15A. The trunk cable is only #12, not sure why #10 would be necessary with that system unless the run is really long, like 200'. As far as a sub-panel, AFAIK there is none required by the NEC or CEC, but my city did require an AC disconnect. I think that was a holdover from when PG&E required it, which is no longer the case. I used a small sub panel instead, and they were OK with that.

The sub panel was redundant, except that I figured it would give me an easy way to add another string of inverters if I ever wanted to. It did come in very handy for something else, though. When I tried to use my Envoy on an outlet near my main panel, it had a hard time communicating with the inverters. I think the problem was either RF from other devices getting into the Envoy, or a low impedance at the panel for the Inverter signals. So I put an outlet on the sub-panel to power the Envoy, put an RF choke on each hot line going back to the main panel, and the problem was cured. The sub-panel let me easily isolate the Envoy and inverters from the rest of the sub panel, something I didn't foresee needing to do.

[solarfrank]

Solar conduit requirements are at NEC 690 the other wiring inside the house at NEC 300.


If your local AHJ required the second ground rod has to be at minimum 6 ft apart.

For the roof conduit and wire size you have to make de-rating for distance from roof to conduit, voltage drop for distance.

You can prove it with calculation for no 12 wire and also no 12 ground but many inspectors and electricians they already know for solar they need minimum no 10 thwn-2 ( rated at 90 )and have truck strock with those wires.

Regarding the breaker if you don't have more than 16 enphase you don't need a subpanel.
I will suggest to use 1/2" - 3/4" flex conduit, no 10 wires ( solar electrician will not carry no 12 or 14), and for the breaker size you can use 2 pole 15A or 20A. It is over-design but will help you from the trouble to explain inspector all the calculation and electrician has stock of those materials.

[JFinch57]

PV DC wires require metal conduit inside the building. (MC might satisfy that requirement - I'd have to look that up)
wires from enphase microinverters? I don't know. (enphase probably has a FAQ about that)

I think he's planning on a pair of 240V breakers - that he has multiple "strings" of enphase coming in, and needs multiple breakers to support them.
I don't know enphase or how many microinverters/strings he's doing - so I'm not sure if multiple 240V breakers is required or if he can do just one.
My advice is to follow the manuf. directions.
And if their directions aren't clear (or aren't exactly like what you're doing) then I'd get someone knowledgable to look at the plans.

I used MC cable inside my house and it passed inspection in NJ (2010). Since the maximum Enphase string size for the M215 is 17 microinverters and he stated that there was only 5+A it's obvious that there will be only one breaker. It's highly unlikely that anyone would wire 2 homeruns at 3 panels each when you can go to 17!

[foo1bar]

It's highly unlikely that anyone would wire 2 homeruns at 3 panels each when you can go to 17!

You're right - I missed the part where he said 6 panels/optimizers.