Concerns about micro inverters

[Naptown]

I don't believe the NEC will allow even AC wiring from a Source to enter a building without some way of disconnecting the circuit at or close to the entry point.

Also the attic usually is not easy to get to so even a disconnect just inside the wall up there may not be accepted by the Inspector. Better to have it outside and accessible so it can be easily turned off to prevent shock or fires.

Then why do they allow 400V DC to run through the attic? (in metallic raceway)

[SunEagle]

Then why do they allow 400V DC to run through the attic? (in metallic raceway)

NEC 690.14 C(1) states that the pv disconnecting means shall be installed at a readily accessible location either outside of the building or structure or inside nearest the point of entry of the system conductors.

There is an exception pointing to section 690.31 (E) that does allow DC wiring to be run in conduit inside of a building where the disconnecting means is remote from the penetration. It would also have to meet some additional requirements.

So I guess it is ok to run a DC circuit through the house but I still don't think you can do so with an AC circuit.

[reagle]

My logic as an end customer in going with microinverters (Sunpower) was:

1. Shading/separation of panels. Everything is connected in parallel on the output side, so a few panels doing funky things for any reason- shade/dirt/snow/internal fault will not prevent others from producing their full output

2. Efficiency- small DC-AC converter with MPPT on panel level is gotta be more efficient than doing it on a DC string level

3. Ease of install/installer idiot-proofness. PLug them into each other. Done.

4. Diagnostics and monitoring on per-panel level. This gets more important as system ages

[russ]

My logic as an end customer in going with microinverters (Sunpower) was:

1. Shading/separation of panels. Everything is connected in parallel on the output side, so a few panels doing funky things for any reason- shade/dirt/snow/internal fault will not prevent others from producing their full output

2. Efficiency- small DC-AC converter with MPPT on panel level is gotta be more efficient than doing it on a DC string level

3. Ease of install/installer idiot-proofness. PLug them into each other. Done.

4. Diagnostics and monitoring on per-panel level. This gets more important as system ages

What about repair or replacement of an inverter? Point 2 has no validity that I can see. For point 4 hire a competent installer.

[bando]

NEC 690.14 C(1) states that the pv disconnecting means shall be installed at a readily accessible location either outside of the building or structure or inside nearest the point of entry of the system conductors.

There is an exception pointing to section 690.31 (E) that does allow DC wiring to be run in conduit inside of a building where the disconnecting means is remote from the penetration. It would also have to meet some additional requirements.

So I guess it is ok to run a DC circuit through the house but I still don't think you can do so with an AC circuit.

we had the installer run over 200 ft conduit EACH through the attic for solar and for a 240V EV outlet in the garage. they have their own separate conduit and what they told me is that the solar is DC and the EV is AC... both punch out of the attic under an eave and then continue their runs. the AC line goes directly to the electrical panel into its own 40amp breaker.

the projects were permitted (and approved) separately.

[SunEagle]

we had the installer run over 200 ft conduit EACH through the attic for solar and for a 240V EV outlet in the garage. they have their own separate conduit and what they told me is that the solar is DC and the EV is AC... both punch out of the attic under an eave and then continue their runs. the AC line goes directly to the electrical panel into its own 40amp breaker.

the projects were permitted (and approved) separately.

Well the circuit for the EV outlet is for a "load" connected to your electrical panel with a 40 amp breaker protecting the wires. That is acceptable to do.

If the AC was from a transformer or power "source" I still do not believe the NEC allows it to be run through a building without having a way to disconnect it either just before the wires and conduit enters the building or right after it enters as long as the disconnect is easily accessible.

It comes down to the safety of someone entering a building that needs to have the electricity turned off first. That is usually performed at the disconnect outside the building or using the Main Circuit Breaker in the Electrical Panel which is supposed to located for easy access. Not up in the attic.

I could be wrong but that is the Electrical Code that I have always followed. I am surprised the same requirements aren't needed for the DC circuit from the solar panels. To me an electrical "source" can be either AC or DC.

[NickSoleil]

Clarifying the NEC codes that apply to microinverters

I am surprised the same requirements aren't needed for the DC circuit from the solar panels. To me an electrical "source" can be either AC or DC.

The requirements for a photovoltaic disconnecting means only apply to DC photovoltaic conductors. The requirements for Disconnecting Means is defined in Section 3 of Article 690.

The specific article in the 2011 code is 690.13, and states clearly, "Means shall be provided to disconnect all current-carrying DC conductors of a photovoltaic system from all other conductors in a building or other structure. The 2014 code clarified that 690.13 only applies to the Ungrounded conductors on the DC side. Since the requirements of 690.13 only apply to the DC conductors of a photovoltaic system, the conduit and wiring of an Enphase microinverter system does not require any additional disconnects, other than the circuit breaker or fuse (OCPD) that is provided at the main service panel or microinverter subpanel.

The NEC is also extremely clear that Photovoltaic Source Circuits and Photovoltaic Output Circuits are DC only. This is true of all recent NEC revisions (2005, 2008, 2011, and 2014). In an Enphase Microinverter system, the only DC conductors are on the roof, between the module and its associated microinverter. The Enphase Microinverter output wiring falls under the definition of Inverter Output Circuits.

One primary advantage of the Enphase Microinverter system is that all field wiring is AC. There is no risk of having any energized conductors inside the building once the main disconnect is shut-off. All of the risks related to Ground Faults and Arc Faults go away. The requirements for DC Arc Fault protection also go away, since the NEC clearly states that arc fault disconnects are only required for DC systems over 80Volts. Those shock and fire risks don't apply in an Enphase system.

Another advantage of Enphase Microinverters is that there is less wiring needed overall. In an Enphase system there is only AC wiring, and that only needs to be run from the roof to the main service panel. In a string inverter system, you have to run the DC wiring to the string inverter, and then run the AC wiring to the main service panel. This means that you will always have at least two wire runs. In a string inverter system, the inverter may need to be located in the garage or another shaded location, and you will need to run extra wiring to get to the string inverter. This can add significant labor costs to the project.

[DanS26]

........Another advantage of Enphase Microinverters is that there is less wiring needed overall. In an Enphase system there is only AC wiring, and that only needs to be run from the roof to the main service panel. In a string inverter system, you have to run the DC wiring to the string inverter, and then run the AC wiring to the main service panel. This means that you will always have at least two wire runs. In a string inverter system, the inverter may need to be located in the garage or another shaded location, and you will need to run extra wiring to get to the string inverter. This can add significant labor costs to the project.

Less wiring needed? Not necessarily so if you are talking wire size as opposed to wire length. If the array is located a long way from the main distribution panel large gauge wire is necessary to mitigate the voltage loss in 240v AC. This point is rarely discussed in micro inverter comparisons. It is a fact that in arrays that are located hundreds of feet from the main distribution panel, such as ground mounts, may require such large gauge wire that the added cost would more than exceed the cost of the string inverters. String inverters can be fed by higher voltage DC which will allow lesser gauge wire lengths at a significant cost savings.

[Naptown]

Less wiring needed? Not necessarily so if you are talking wire size as opposed to wire length. If the array is located a long way from the main distribution panel large gauge wire is necessary to mitigate the voltage loss in 240v AC. This point is rarely discussed in micro inverter comparisons. It is a fact that in arrays that are located hundreds of feet from the main distribution panel, such as ground mounts, may require such large gauge wire that the added cost would more than exceed the cost of the string inverters. String inverters can be fed by higher voltage DC which will allow lesser gauge wire lengths at a significant cost savings.

And the Engage cable can get a bit pricey added to the additional expense of the microinverters.
About 200' is about as far as I will go with micro's after that strictly string inverters.
And Micro's only when shading is an issue that cannot be overcome by creative stringing.

[DanS26]

And the Engage cable can get a bit pricey added to the additional expense of the microinverters.
About 200' is about as far as I will go with micro's after that strictly string inverters.
And Micro's only when shading is an issue that cannot be overcome by creative stringing.

I have two ground mount arrays located 250' and 300' feet from the main distribution panel. My wire savings alone using high voltage DC was enough to offset the cost of two Fronius 7.5kw inverters. Not only wire size was less but number of wires in conduit was less. Significant savings.

Every project is different and it is important that the alternative designs be investigated to obtain the best ROI for each situation. So many times we see the marketing hype cover up the the best designs for the project at hand.

[bcroe]

I have two ground mount arrays located 250' and 300' feet from the main distribution panel. My wire savings alone using high voltage DC was enough to offset the cost of two Fronius 7.5kw inverters. Not only wire size was less but number of wires in conduit was less. Significant savings.

Every project is different and it is important that the alternative designs be investigated to obtain the best ROI for each situation. So many times we see the marketing hype cover up the the best designs for the project at hand.

The situation here is almost identical; big benefit from the high voltage DC. Hit 409 VDC in the
0 degree F temps today. The AC portion was already in place, at no cost to the installation. Bruce Roe

[SunEagle]

The requirements for a photovoltaic disconnecting means only apply to DC photovoltaic conductors. The requirements for Disconnecting Means is defined in Section 3 of Article 690.

The specific article in the 2011 code is 690.13, and states clearly, "Means shall be provided to disconnect all current-carrying DC conductors of a photovoltaic system from all other conductors in a building or other structure. The 2014 code clarified that 690.13 only applies to the Ungrounded conductors on the DC side. Since the requirements of 690.13 only apply to the DC conductors of a photovoltaic system, the conduit and wiring of an Enphase microinverter system does not require any additional disconnects, other than the circuit breaker or fuse (OCPD) that is provided at the main service panel or microinverter subpanel.

The NEC is also extremely clear that Photovoltaic Source Circuits and Photovoltaic Output Circuits are DC only. This is true of all recent NEC revisions (2005, 2008, 2011, and 2014). In an Enphase Microinverter system, the only DC conductors are on the roof, between the module and its associated microinverter. The Enphase Microinverter output wiring falls under the definition of Inverter Output Circuits.

One primary advantage of the Enphase Microinverter system is that all field wiring is AC. There is no risk of having any energized conductors inside the building once the main disconnect is shut-off. All of the risks related to Ground Faults and Arc Faults go away. The requirements for DC Arc Fault protection also go away, since the NEC clearly states that arc fault disconnects are only required for DC systems over 80Volts. Those shock and fire risks don't apply in an Enphase system.

Another advantage of Enphase Microinverters is that there is less wiring needed overall. In an Enphase system there is only AC wiring, and that only needs to be run from the roof to the main service panel. In a string inverter system, you have to run the DC wiring to the string inverter, and then run the AC wiring to the main service panel. This means that you will always have at least two wire runs. In a string inverter system, the inverter may need to be located in the garage or another shaded location, and you will need to run extra wiring to get to the string inverter. This can add significant labor costs to the project.

I agree with all you have stated. The question comes up when someone wants to run the AC wiring from a Microinverter system "through" the home's attic and then back outside to a disconnect switch. I say that can't be done because the AC wiring is considered a "source" and must have a way to disconnect the power before it enters a building's attic.

As for a DC string inverter system. Unless it is a very small system the DC voltage will probably exceed 80 Volts between the panels and string inverter which would then need to comply with requiring arc fault disconnects.

So I am having an issue the code which allows this DC wiring to enter an attic and then come back out to a disconnect device. I feel there should be a disconnect "before" it enters the attic but the NEC states in section 690.14 (C) (1) "Location" that if the DC wiring comply with section 690.31 (E) "which is running the wire in a conduit" then the disconnecting means can be remotely located from the point of entry.

Just saying I don't like the idea of energized wires running through my house without having a way to disconnect them before they enter it.

[peakbagger]

I have central inverter on my rooftop array and Solar Deck box mounted in the roof to transition from the PV cables to the metallic conduit in the attic. It was equipped to be a combiner box but with one string I had no need for a combiner. Nevertheless I used one of the combiner blocks so there is a disconnect on the DC on the roof but it is not accessible (requires removing 4 screws). My preference would be for them to install a big lever with gasket to shut off the combiner switches from the exterior but I expect it would raise the cost.

[inetdog]

Just saying I don't like the idea of energized wires running through my house without having a way to disconnect them before they enter it.

It is largely a matter of where you want the disconnect to be.
For maintenance purposes you will still want to have a string or combiner level disconnect even if it is just unplugging the MC4 connectors after the load has been shut down.
The code exception relieves you of the requirement for an additional disconnect after the combiner, right at the point where the DC conductors enter the building.

It would be a colossal pain to provide a readily accessible disconnect before the wires enter the building. That will end up requiring remotely operated switches or contactors.
But the NEC 2014 requirements for a DC emergency disconnect that makes the roof safe for first responders has taken us a long way in this direction.
Currently only microinverters and combiners with integral remote power shutoff meet those requirements AFAIK.

[SunEagle]

It is largely a matter of where you want the disconnect to be.
For maintenance purposes you will still want to have a string or combiner level disconnect even if it is just unplugging the MC4 connectors after the load has been shut down.
The code exception relieves you of the requirement for an additional disconnect after the combiner, right at the point where the DC conductors enter the building.

It would be a colossal pain to provide a readily accessible disconnect before the wires enter the building. That will end up requiring remotely operated switches or contactors.
But the NEC 2014 requirements for a DC emergency disconnect that makes the roof safe for first responders has taken us a long way in this direction.
Currently only microinverters and combiners with integral remote power shutoff meet those requirements AFAIK.

Even if it didn't look pretty I would still have the wiring and conduit from the solar panels run along the roof outside the house and then down to a disconnect.

The idea of having energized wires going through my attic or home with no easy way to kill the power source scares me. I maybe over sensitive but I have seen enough electrical fires in conduit fittings to want to have the ability to easily kill the power.