AC Inverter Output Wiring

[shortcircuit2]

Wouldn't 225.31 require the disconnect you are discussing and 225.32 tell you where to put it?

 

[jaggedben]

Wouldn't 225.31 require the disconnect you are discussing and 225.32 tell you where to put it?

No. The situation is not a separate building supplied by a branch circuit or feeder.

 

[kdearth]

Wouldn't 225.31 require the disconnect you are discussing and 225.32 tell you where to put it?

I'm not sure. Perhaps a good question for the code experts.

I did propose the issue of safety concerning the microinverter AC output wiring being run through the attic. The inspectors response was something along the lines of having the disconnect on the "wrong end" of the conductors if they were to start a fire. I thought the whole purpose of the AC disconnect, irregardless of where it located, was to provide overcurrent protetion in which case the inverters would shut down and there would bo no power in the AC inverter output conductors. If they were DC conductors run through the attic wouldn't there still be power, coming form the panels, even if the DC disconnect were thrown? Essentially with the inverter placed on the roof, there is no worry of having energized conductors through the attic if something were to go wrong

He said with my setup, I would burn my house down. I guess there are many fire hazard systems currently permitted and installed. I personally know of a couple.

 

[jaggedben]

Way too late to submit changes for the 2014 code. The ROP and draft for the 2014 has been published on the NFPA website.

Thanks for educating me on the code updating process. I took a look.

It turns out that the relevant sections will be re-written in the 2014 code, and that the section that will now address this will be 690.13. And furthermore, 690.13 will make specific reference to dc conductors. Unfortunately (IMO), it does not look like they will fully adopt one of John Wiles proposals that included adding 'dc' to all of the requirements mentioned in the current 690.14(C). That would have made it crystal clear.

In any case, the good news is that the problem our OP is having should be significantly reduced once the 2014 code takes force.

 

[jaggedben]

I thought the whole purpose of the AC disconnect, irregardless of where it located, was to provide overcurrent protetion in which case the inverters would shut down and there would bo no power in the AC inverter output conductors.

That's the purpose of the AC OCPD, not the readily accessible disconnect. Sometimes they can be the same piece of equipment, but more often they are not.

If they were DC conductors run through the attic wouldn't there still be power, coming form the panels, even if the DC disconnect were thrown? Essentially with the inverter placed on the roof, there is no worry of having energized conductors through the attic if something were to go wrong

Exactly. That's why 690.14 was written to address this issue. And that's why John Wiles, the original writer of 690, is now trying to get this section to reference only dc conductors, because it was written to address dc conductor issues, not ac conductor issues.

He said with my setup, I would burn my house down.

And he is still wrong. You can run NM through walls or an attic to a 240V dryer circuit, and this will be totally code compliant and absolutely no more or less likely to burn a house down than your inverter circuit.

 

[kdearth]

That's the purpose of the AC OCPD, not the readily accessible disconnect. Sometimes they can be the same piece of equipment, but more often they are not.



Exactly. That's why 690.14 was written to address this issue. And that's why John Wiles, the original writer of 690, is now trying to get this section to reference only dc conductors, because it was written to address dc conductor issues, not ac conductor issues.



And he is still wrong. You can run NM through walls or an attic to a 240V dryer circuit, and this will be totally code compliant and absolutely no more or less likely to burn a house down than your inverter circuit.

I seriously think he REFUSES to understand this. He has made it a point to tell me about his 30+ years experience and that the part I am not accepting of is essentially taught in basic electrician wiring courses. Oddly enough I am an electrical engineer. I actually have about 15-20 electricians that I work with. I suppose they must all be experts at solar NEC requirements too. I think he is trying to apply his real world electrical expertise and implying that automatically makes him an expert at solar as it relates to the NEC. To me those are different beast.

 

[shortcircuit2]

No. The situation is not a separate building supplied by a branch circuit or feeder.

I don't see where it 225.31 states that it applies to seperate buildings only.

 

[ggunn]

I'm not sure. Perhaps a good question for the code experts.

I did propose the issue of safety concerning the microinverter AC output wiring being run through the attic. The inspectors response was something along the lines of having the disconnect on the "wrong end" of the conductors if they were to start a fire. I thought the whole purpose of the AC disconnect, irregardless of where it located, was to provide overcurrent protetion in which case the inverters would shut down and there would bo no power in the AC inverter output conductors. If they were DC conductors run through the attic wouldn't there still be power, coming form the panels, even if the DC disconnect were thrown? Essentially with the inverter placed on the roof, there is no worry of having energized conductors through the attic if something were to go wrong

He said with my setup, I would burn my house down. I guess there are many fire hazard systems currently permitted and installed. I personally know of a couple.

I feel your pain. It matters not which end of the conductors the disco is on in the AC circuit of a PV inverter; if power is interrupted on the AC side, the inverter shuts down and the conductors are de-energized. On the DC side it does matter because when a DC disco at the inverter is opened (or when the inverter senses a ground fault and shuts down), although current stops flowing, the DC voltage is still present on the conductors and a short can cause arcing and therefore a fire. That's why in many jurisdictions an additional DC disco is required on the roof for a central inverter PV system when the DC is routed through the building envelope. Others simply may not allow you to run DC conductors through a building at all. But you know all this, right?

Can you still get out of this morass by running a bit of conduit? Sad to say, it may be the simplest way to get on with your life.

 

[don_resqcapt19]

Thanks for educating me on the code updating process. I took a look.

It turns out that the relevant sections will be re-written in the 2014 code, and that the section that will now address this will be 690.13. And furthermore, 690.13 will make specific reference to dc conductors. Unfortunately (IMO), it does not look like they will fully adopt one of John Wiles proposals that included adding 'dc' to all of the requirements mentioned in the current 690.14(C). That would have made it crystal clear.

In any case, the good news is that the problem our OP is having should be significantly reduced once the 2014 code takes force.

Remember that there are 3 more chances for what you see now to change before it becomes part of the code. The first is the comment process, second is the annual meeting motion and voting process and then there is the Standards Council.

 

[kdearth]

I feel your pain. It matters not which end of the conductors the disco is on in the AC circuit of a PV inverter; if power is interrupted on the AC side, the inverter shuts down and the conductors are de-energized. On the DC side it does matter because when a DC disco at the inverter is opened (or when the inverter senses a ground fault and shuts down), although current stops flowing, the DC voltage is still present on the conductors and a short can cause arcing and therefore a fire. That's why in many jurisdictions an additional DC disco is required on the roof for a central inverter PV system when the DC is routed through the building envelope. Others simply may not allow you to run DC conductors through a building at all. But you know all this, right?

Can you still get out of this morass by running a bit of conduit? Sad to say, it may be the simplest way to get on with your life.

That's exactly what I have been trying to explain to him. Twice in fact. Both times he became extremely upset and accussed me trying to explain AC/DC circuit concepts or implying he knows nothing about disconnects. I think he clearlymissed the point. When you become emotional, that is easy to do. Here is why I still don't think he gets it:

Him: " no one would be able to turn off the conductors running through the building because they would be ahead of the disconnect""

ME: The direction of power flow is never to the panels. The conductors "ahead" of the disconnect, running from the AC disconnect to the main CB panel, will not de-energize, no matter where the disconnect is because they are back-fed by the main CB panel.

I added more to this simply explaining a scenario whereby I mounted the disconnect inside the attic near where the conductors enter the building and it was deemed readily-accessible. This would satisfy his requirements. Problem is,when I pull the disconnect handle, the conductors running through the attic to the main CB panel will remain energized. Wont the main CB panel backfeed the AC disconnect? It seems what he deems ok is far more dangerous than what he deems not ok.

Am I crazy? Maybe I am!!

 

[ggunn]

That's exactly what I have been trying to explain to him. Twice in fact. Both times he became extremely upset and accussed me trying to explain AC/DC circuit concepts or implying he knows nothing about disconnects. I think he clearlymissed the point. When you become emotional, that is easy to do. Here is why I still don't think he gets it:

Him: " no one would be able to turn off the conductors running through the building because they would be ahead of the disconnect""

ME: The direction of power flow is never to the panels. The conductors "ahead" of the disconnect, running from the AC disconnect to the main CB panel, will not de-energize, no matter where the disconnect is because they are back-fed by the main CB panel.

I added more to this simply explaining a scenario whereby I mounted the disconnect inside the attic near where the conductors enter the building and it was deemed readily-accessible. This would satisfy his requirements. Problem is,when I pull the disconnect handle, the conductors running through the attic to the main CB panel will remain energized. Wont the main CB panel backfeed the AC disconnect? It seems what he deems ok is far more dangerous than what he deems not ok.

Am I crazy? Maybe I am!!

It seems to me that your response did not directly address his point. He is correct that the conductors from the inverters are "ahead" (I hate that ambiguous term) of the disco, but that fact is irrelevant because 1) when you open the disco, the inverters shut down and de-energize the conductors, and 2) the output from an inverter is incapable of feeding a short. Has anyone explained UL 1741 to this guy?

You are absolutely correct that if a short occurs in your AC line, it is current from your service panel that will feed it, not the current from your inverters; the inverters will shut down. That's why we backfeed a breaker instead of attaching directly to the busbars.

I ask again: Will putting your conductors in conduit make them happy? Why not just do it and live to fight another day? I am an electrical engineer as well, and I understand an engineer's propensity for going to the mat over an esoteric point (I drive my wife crazy sometimes), but we must live in the real world. To paraphrase an old adage, the inspector may not always be right but he is always the inspector.

 

[kdearth]

It seems to me that your response did not directly address his point. He is correct that the conductors from the inverters are "ahead" (I hate that ambiguous term) of the disco, but that fact is irrelevant because 1) when you open the disco, the inverters shut down and de-energize the conductors, and 2) the output from an inverter is incapable of feeding a short. Has anyone explained UL 1741 to this guy?

You are absolutely correct that if a short occurs in your AC line, it is current from your service panel that will feed it, not the current from your inverters; the inverters will shut down. That's why we backfeed a breaker instead of attaching directly to the busbars.

I ask again: Will putting your conductors in conduit make them happy? Why not just do it and live to fight another day? I am an electrical engineer as well, and I understand an engineer's propensity for going to the mat over an esoteric point (I drive my wife crazy sometimes), but we must live in the real world. To paraphrase an old adage, the inspector may not always be right but he is always the inspector.

Speaking of UL this is what was at the end of a rather lengthy email he sent in regards to the AC/DC connectors of the enphase system meeting the exception to 690.17. If I am reading this correctly couldnt this have just saved a lot of headache?

"If you can get the testing lab to weigh in with us in writing that the specific connectors on your system do in fact meet that criteria then your problem is over because your disconnecting means would be outside."

We seem to be on pretty good terms again after I attempted to liven up the conversation a bit. There is a little bit of hazing back and forth now in good fun. Amazingly it was after I told him of my job. He even thanked me for providing some of my technical expertise.

 

[kdearth]

It seems this has been all one big misunderstanding. It appears the inspectors were arguing from the point of the AC disconnect on the exterior of my garage being the first disconnect. I was arguing from the point of the Enphase connectors being suitable for the first disconnect. The irony in all this is that at no point, in talking with 3 different inspectors, did any one of them understand nor ask about the Enphase connectors being acceptable as disconnects. I am not sure if this is a failure on the part of the inspectors for not fully understanding my system or on my part for not providing more documentation applicable towards the microinverter connectors. Perhaps a bit of both.

 

[jxofaltrds]

It seems this has been all one big misunderstanding. ***** Perhaps a bit of both.

That never happens here! :angel:

 

[jaggedben]

I don't see where it 225.31 states that it applies to seperate buildings only.

It is in Part II of 250, the title of which is "Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit".

I would not have thought that any of Part II would apply to a building or structure that has the service disconnecting means. Now I'm curious what others on this forum think.

 

[jaggedben]

It seems this has been all one big misunderstanding. It appears the inspectors were arguing from the point of the AC disconnect on the exterior of my garage being the first disconnect. I was arguing from the point of the Enphase connectors being suitable for the first disconnect. The irony in all this is that at no point, in talking with 3 different inspectors, did any one of them understand nor ask about the Enphase connectors being acceptable as disconnects. I am not sure if this is a failure on the part of the inspectors for not fully understanding my system or on my part for not providing more documentation applicable towards the microinverter connectors. Perhaps a bit of both.

Wow. I'm glad it worked out. :lol:

Frankly though, from what you've said, I don't think the conclusion they reached is really correct or helpful in the long run. The conductors inside the building are not made any safer (or less safe) by the presence of a disconnect on the roof (whether that disco is the connectors or a separate one). I agree with what ggunn said, it sounds like someone needs to explain UL 1741 to them. The bottom line is that they should understand that AC inverter output circuits on grid-tied systems are made safe in the same way as any other AC circuit. That is, with a disco and OCPD at the grid end of the circuit.

I'm starting to think that we need a simple addition to 690 (and/or 705) that would say something roughly along the lines of: "Inverter output circuits for utility interactive systems shall be permitted to use any methods that are permitted by Article 300. This shall not apply to systems capable of stand alone operation." It sounds like the 2014 code will likely take us at least a step in this direction my specifying that the disconnecting means requirements in 690 apply to dc disconnects.

 

[kdearth]

Wow. I'm glad it worked out. :lol:

Frankly though, from what you've said, I don't think the conclusion they reached is really correct or helpful in the long run. The conductors inside the building are not made any safer (or less safe) by the presence of a disconnect on the roof (whether that disco is the connectors or a separate one). I agree with what ggunn said, it sounds like someone needs to explain UL 1741 to them. The bottom line is that they should understand that AC inverter output circuits on grid-tied systems are made safe in the same way as any other AC circuit. That is, with a disco and OCPD at the grid end of the circuit.

I'm starting to think that we need a simple addition to 690 (and/or 705) that would say something roughly along the lines of: "Inverter output circuits for utility interactive systems shall be permitted to use any methods that are permitted by Article 300. This shall not apply to systems capable of stand alone operation." It sounds like the 2014 code will likely take us at least a step in this direction my specifying that the disconnecting means requirements in 690 apply to dc disconnects.

I agree, I don't see how this IS any different. From the inspectors point of view and the one in which they argued from, they now understand that there is a disconnect before any conductors enter the building. In the grand scheme of things, as far as the danger these conductors present, there is no difference whether it is on the roof or on the wall.

The chief inspectors assistant came out yesterday. He was the most pleasant gentleman in that office yet. Very personable. Pretty much the opposite of the original inspector who barely spoke. I asked him how many systems they have encountered of this kind and it would seem none. I had already removed a panel so I could kind of talk him through and show him how it works, the components, the wiring scheme, etc. I also gave him the spec sheets for the Engage cable proving UL certification and the CSA sheet. He was perfectly happy with those and it was as easy as that. Now I am wondering, had the first inspector been more proactive and asked more questions, could this entire issue have been avoided? He had the drawings and spec sheets.

 

[tallgirl]

Speaking of UL this is what was at the end of a rather lengthy email he sent in regards to the AC/DC connectors of the enphase system meeting the exception to 690.17. If I am reading this correctly couldnt this have just saved a lot of headache?

"If you can get the testing lab to weigh in with us in writing that the specific connectors on your system do in fact meet that criteria then your problem is over because your disconnecting means would be outside."

We seem to be on pretty good terms again after I attempted to liven up the conversation a bit. There is a little bit of hazing back and forth now in good fun. Amazingly it was after I told him of my job. He even thanked me for providing some of my technical expertise.

The testing lab already weighed in when they certified the products to whatever certification was provided. Get the inspector a copy of the compliance documents for the inverter (should be available from the vendor) and be done with it.

 

[shortcircuit2]

It is in Part II of 250, the title of which is "Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit".

I would not have thought that any of Part II would apply to a building or structure that has the service disconnecting means. Now I'm curious what others on this forum think.

How does Part II of 250 have anything to do with 225?

 

[jaggedben]

How does Part II of 250 have anything to do with 225?

Typo, I meant 225, and that is the title of part II of 225.