Micro inverter setup

Status
Not open for further replies.
G

gonzo1

Member
Location
phiadelphia,PA
Hello all,i'm dotting my I's and crossing my t's on research for a future install.I am a licensed Electrician in the city of philadelphia,figured i'd get that out of the way before i get the warning for not being a pro.My question;I'm looking at going with a small
(under 2kw set up with future expansion) I like the enphase micro's, pretty cut and dry setup.I was looking at an Enphase white sheet and noticed that on the d/c side of the inverter it provides gfdi protection through integrated grounding does not even require attachment GEC although AHJ may still want too see it.I'm going to assume that GFDI protection is carried over to the a/c side.(please tell me if i am wrong on this)My concern with the Enphase m250 is that for arc fault protection it simply refers to the inexistance of a backed arc fault breaker,and therefore being exempt from needingAFCI protection.Now as per 690.11 Manufacturers of string inverters are now required to provide arc fault protection,now it would
seem to me that string inverters have that one advantage over micro's.So A:if one were to install an arc fault breaker from the trunk cable after the array to the output side of the micro's, in a proper NEMA disconnect enclosure of course ( assuming a 240 volt AFCI breaker exist)would that now dress the line load condition?I realize that i'm not "discovering the solution for arc fault protection for Enphase inc"I just would like to know why that wouldn't work. I understand that as per 690.12 the M250 is compliant with rapid shut down so that, along with GPDI protection is tipping the scales to a micro inverter install for me.not to mention don't like the idea of higherD/C voltages in my home,The only 600 volt d/c i want to be around is the Frankford El train.Thanks
 
AFAIK the micros do not include AC GF detection, but I might be wrong about that.

The NEC is particular about not connecting a feeder which includes secondary generation backfeed as well as normal loads through a GFCI breaker, since it would be possible for the secondary generation to feed current into a ground fault without necessarily tripping that GFCI breaker.

As long as a GFCI breaker carries only backfeed current, it would be OK except for the problem that AFAIK no GFCI breaker is rated for reverse current flow.

Similar problems arise when looking at AFCI too.
 
DC GFDI is not 'carried over' to the ac side in any type of inverter, that I know of.

Also, DC and AC arc fault protection are completely different animals, in real life and in the code, so it's best to not to conflate them in any discussion.

690.11 does not apply to Enphase inverters because the DC circuits (i.e. between each module and micro-inverter) are less than 80 volts max. So we can stop talking about 690.11.

The problem you may have with your AHJ if you're on the 2014 code is 705.12(D)(6), which requires listed AFCI protection for the exposed Enphase trunk cable. The issue is that AFCI breakers all seem to be labeled for line and load, and thus violate 705.12(D)(4). So that's a catch-22 and your best bet is to appeal to the third paragraph of 90.4 which says that AHJs may permit the latest products to be used when the code requires products that don't exist yet.

I could be misremembering, but I believe in the 2017 code they eliminated 705.12(D)(6) because the right breakers still don't exist, three years later.

Practically speaking, how worried should you be about these types of protections if your roof material is class A fire resistant, such as asphalt shingle or concrete tile? Not very, in my opinion. Now if you have a wood shake roof, maybe worry a little more about it...(and there are other reasons to not install solar on that type of roof).
 
jaggedben said:
DC GFDI is not 'carried over' to the ac side in any type of inverter, that I know of.

Also, DC and AC arc fault protection are completely different animals, in real life and in the code, so it's best to not to conflate them in any discussion.

690.11 does not apply to Enphase inverters because the DC circuits (i.e. between each module and micro-inverter) are less than 80 volts max. So we can stop talking about 690.11.

The problem you may have with your AHJ if you're on the 2014 code is 705.12(D)(6), which requires listed AFCI protection for the exposed Enphase trunk cable. The issue is that AFCI breakers all seem to be labeled for line and load, and thus violate 705.12(D)(4). So that's a catch-22 and your best bet is to appeal to the third paragraph of 90.4 which says that AHJs may permit the latest products to be used when the code requires products that don't exist yet.

I could be misremembering, but I believe in the 2017 code they eliminated 705.12(D)(6) because the right breakers still don't exist, three years later.

Practically speaking, how worried should you be about these types of protections if your roof material is class A fire resistant, such as asphalt shingle or concrete tile? Not very, in my opinion. Now if you have a wood shake roof, maybe worry a little more about it...(and there are other reasons to not install solar on that type of roof).
Click to expand...

I'm not overly concerned,just curious as to how I would achieve arc protection.I'm in no way an alarmist,the likelihood of having an arc fault or ground fault is minimal,but yet still probable.Also, simply because my roof is fire rated does not mean that one shouldn't be concerned with high temperature arcing or ground faults.That would be akin to not storing flammables properly cause one has a functioning sprinkler system.As we can see with progressing code cycles,AFCI protection has been expanded more and more,so i think it may be logical to assume that one day inverter output ckt's will also have AFCI requirements,then again i may be wrong.
 
gonzo1 said:
I'm not overly concerned,just curious as to how I would achieve arc protection.I'm in no way an alarmist,the likelihood of having an arc fault or ground fault is minimal,but yet still probable.Also, simply because my roof is fire rated does not mean that one shouldn't be concerned with high temperature arcing or ground faults.That would be akin to not storing flammables properly cause one has a functioning sprinkler system.As we can see with progressing code cycles,AFCI protection has been expanded more and more,so i think it may be logical to assume that one day inverter output ckt's will also have AFCI requirements,then again i may be wrong.
Click to expand...
It is hard to see how an AFCI integrated with the inverter or micro could do anything to protect the wiring against arc faults, since it would remain energized from the grid side.
 
gonzo1 said:
I'm not overly concerned,just curious as to how I would achieve arc protection.I'm in no way an alarmist,the likelihood of having an arc fault or ground fault is minimal,but yet still probable.Also, simply because my roof is fire rated does not mean that one shouldn't be concerned with high temperature arcing or ground faults.That would be akin to not storing flammables properly cause one has a functioning sprinkler system.As we can see with progressing code cycles,AFCI protection has been expanded more and more,so i think it may be logical to assume that one day inverter output ckt's will also have AFCI requirements,then again i may be wrong.
Click to expand...

You may or may not be right about that last point, but my point (my opinion really) is that an exposed wire harness on a fire rated roof is probably not measurably more dangerous than just having a hardwired appliance circuit inside a conduit. Do you feel you need to put AFCI on an oven circuit? Either could theoretically be prone to some kind of resistive fault that wouldn't trip a breaker. I think that the reason for the code passage is probably thinking that the Enphase trunk cable falls in a similar category as extension cords plugged into receptacles inside a house. But if you ask me, wiring above a fire rated roof that is not readily accessible is a whole level more safe. (Again, above a non-fire rated roof, maybe different.)

Presumably if manufacturers can figure out how to make and list an AFCI breaker that can be backfed we'll see that requirement be enforced in some places. But for the time being I don't think that's happening.
 
GoldDigger said:
It is hard to see how an AFCI integrated with the inverter or micro could do anything to protect the wiring against arc faults, since it would remain energized from the grid side.
Click to expand...

Excellent point,then the need for a backfed AFCI seems to be the viable option.So then my hamster in the treadmill (my brain or lack thereof)starts running,could this be accomplished by a shunt trip breaker on your grid side?I have to reiterate,simply curious as i would not install anything that isn't rated or acknowledged by AHJ.
 
jaggedben said:
You may or may not be right about that last point, but my point (my opinion really) is that an exposed wire harness on a fire rated roof is probably not measurably more dangerous than just having a hardwired appliance circuit inside a conduit. Do you feel you need to put AFCI on an oven circuit? Either could theoretically be prone to some kind of resistive fault that wouldn't trip a breaker. I think that the reason for the code passage is probably thinking that the Enphase trunk cable falls in a similar category as extension cords plugged into receptacles inside a house. But if you ask me, wiring above a fire rated roof that is not readily accessible is a whole level more safe. (Again, above a non-fire rated roof, maybe different.)

Presumably if manufacturers can figure out how to make and list an AFCI breaker that can be backfed we'll see that requirement be enforced in some places. But for the time being I don't think that's happening.
Click to expand...

This is turning out to be a very interesting "conversation"it's like going to the office party with the wife and finding someone who doesn't care to talk about janice in accounting.Thanks for all the replies.You're correct about not needing protection on an oven circuit,
But remember for years we would supply a branch circuit for say,smoke detectors and not ever need AFCI protection,not so by today's standards.We are required to install a combination type AFCI.Same with lighting our resistive loads with the introduction of LED lighting have exponentially become less and less,and yet AFCI requirements have become more stringent.But as the technology advances and solar prices drop we begin to see more and more DIY's taking on PV projects.I cannot tell you how many videos there are on youtube with weekend warriors running romex straight into their service panels,scary!You can rest assured that my install not only will be code compliant,but will be torqued to specs meggard out and will be completely enclosed in EMT,not the case with joe homeowner.my point is 1)AFCI protection is here to stay,and some would argue that the code has become a little too aggressive with enforcement (for instance alterations of circuits now requiring arc fault breakers)So in essence having an installation that is not more or less susceptible to damage,misuse,neglect,and or improper installation just seems to be headed in the same direction with arc fault protection that in years past wasn't the case.2)if micro inverter manufacturers could implement AFCI and GFDI protection would that tilt the scales in their favor?food for thought.thanks
 
inverter setup

inverter setup

Hi jag,I keep researching this wonderful myriad of of confusion that is solar and inter connection.I was watching a youtube video (point of interconnection to utility power)and at 1:18:00 they make mention of ungrounded transformer less inverters having gfdi on d/c side automatically carrying over to a/c side.And I know that the M250 does not require connection to EGC it to is ungrounded(on the d/c side of course) isolated,and gfdi protectied.I'd like you to watch the video I would recommend the whole hour But i know folks are busy and sometimes we can't find an hour to sit and watch a video,so if that's the case at 1:18:00 or there about they make mention of gfdi carrying through to a/c side.Sometimes I can get ahead of myself and completely misunderstand, so if you or anyone else for that matter will watch and let me know if i processed that info correctly?If i did,not the first time nor shall it be the last.Thanx
jaggedben said:
DC GFDI is not 'carried over' to the ac side in any type of inverter, that I know of.

Also, DC and AC arc fault protection are completely different animals, in real life and in the code, so it's best to not to conflate them in any discussion.

690.11 does not apply to Enphase inverters because the DC circuits (i.e. between each module and micro-inverter) are less than 80 volts max. So we can stop talking about 690.11.

The problem you may have with your AHJ if you're on the 2014 code is 705.12(D)(6), which requires listed AFCI protection for the exposed Enphase trunk cable. The issue is that AFCI breakers all seem to be labeled for line and load, and thus violate 705.12(D)(4). So that's a catch-22 and your best bet is to appeal to the third paragraph of 90.4 which says that AHJs may permit the latest products to be used when the code requires products that don't exist yet.

I could be misremembering, but I believe in the 2017 code they eliminated 705.12(D)(6) because the right breakers still don't exist, three years later.

Practically speaking, how worried should you be about these types of protections if your roof material is class A fire resistant, such as asphalt shingle or concrete tile? Not very, in my opinion. Now if you have a wood shake roof, maybe worry a little more about it...(and there are other reasons to not install solar on that type of roof).
Click to expand...
 
Yes, I suppose I glossed over some fine points when I said above that DC GFDI does not 'carry over' to the AC side. But two points...

1) The Enphase M250 is not a transformerless inverter so that interesting discussion does not apply. (In fact Enphase are the only inverters I know of that are both ungrounded and have a transformer.)

2) Although in a transformerless inverter the GFDI may detect fault current flowing directly back to the AC system, it cannot detect faults on the AC side of the inverter and will not de-energize the AC conductors to the inverter.

By the way, you didn't include a link to the video...
 
jaggedben said:
1) The Enphase M250 is not a transformerless inverter so that interesting discussion does not apply. (In fact Enphase are the only inverters I know of that are both ungrounded and have a transformer.)
Click to expand...
Are you sure about that? I have seen the guts of an Enphase micro and I do not remember a transformer on the AC output.
 
Engineer#4827502 said:
Looks like the transformer in that circuit is part of the inversion as opposed to connected to the AC output after the power is inverted. ...
Click to expand...

I hadn't notice that before. But does it make any sense? A transformer placed on the DC side really wouldn't do anything, right? It makes me suspect the drawing is wrong. However the document also repeatedly states the the DC side is isolated.
 
Great find guys!i've seen that schematic over and over and never realized that the xformer is on the dc side.So is it safe to assume the drawing is wrong?or is the enphase tranformerless like many of the newer string inverters?
 
I'm no engineer, so I ask in earnest...

What kind of device could convert ~30V to >200V besides a transformer?

What kind of device could do this with DC?
 
That circuit is similar to a flyback converter but without the diode would output AC. The switch will vary the duty cycle such that AC would be achieved on the high side. With the right winding ratios and controls, it could output 240VAC from 30VDC.
 
The key point is that the pu nolse transformer in the DC to DC converter can be a single winding with no isolation, a multiple tap autotransformer coil or two coils with isolation. That is a design decision.
 
jaggedben said:
I'm no engineer, so I ask in earnest...

What kind of device could convert ~30V to >200V besides a transformer?

What kind of device could do this with DC?
Click to expand...
A DC to DC converter. These things usually have an intermediate AC step where the actual voltage conversion happens. I don't know about 30V to 200V, though; that seems kind of extreme.
 
Status
Not open for further replies.
Top