transformer inverter vs. transformerless inverter - worth the savings?

[bcroe]

This is what you said:



This is what the article says:



In grid tie systems, you don't ground the DC conductor directly, separately from the AC ground. The DC ground is provided through the inverter, shared with the AC ground, and in 2017 NEC language, is considered "functionally grounded", not "solidly grounded" because there is a fuse in the circuit.

There is more flexibility in how you handle the equipment ground, but that is true regardless of whether you use a transformer based or transformerless inverter.

Lets not confuse the grounding of the PV framework (solid), with the PV DC conductors, which in my system
ground negative through a small fuse in the inverter, in turn monitored by a GFI circuit. Bruce Roe

[sensij]

This is what you said:

before buying a transformer inverter, i would want to make certain the AHJ will approve separate grounding (a/c and d/c separate).

This is what the article says:

Now, the only type of PV system permitted to be solidly grounded has only one or two PV source circuits, and no DC circuits on or in a building. This limits these applications to small, load-focused, PV-direct systems and perhaps some smaller battery-based systems.

In grid tie systems, you don't ground the DC conductor directly, separately from the AC ground. The DC ground is provided through the inverter, shared with the AC ground, and in 2017 NEC language, is considered "functionally grounded", not "solidly grounded" because there is a fuse in the circuit.

There is more flexibility in how you handle the equipment ground, but that is true regardless of whether you use a transformer based or transformerless inverter.

[Jest Waitn]

That is not going to happen, so forget about it. It is required by code, and it would be extremely dangerous if you did not. additionally it can wreak havoc on your electrical system. To the point your TV and electronics would not work. So just get that idea out of your head as it is Best Practice.

how does this differ from what i said?

https://www.homepower.com/articles/solar-electricity/design-installation/code-corner-earth-shifting-change-grounding

[Sunking]

i'm not refuting what you say or arguing with you, but in the below article on pv system ground faults, how does the last paragraph on the page relate to what you say? it seems that the author is saying the pv ground should NOT be carried into the inverter. this is for a grounded pv system (i assume the author is referring to using a transformer inverter).

http://solarprofessional.com/article...2#.WSXmMHUrJpR

No problem I did not take it that you are arguing or debating. The problem you are having is not understanding what the author is trying to tell you. You came away with the impression the AC and DC system grounds must be isolated and separate from each other. That is not what the author is saying. If that is what he is implying, then he should be shot as a pretender and fraud, because that can fry your equipment and get you killed.

I don't want to dive into the technical part because it is out of the scope of this forum, and frankly quite a long and boring lecture not all professionals ever get their heads wrapped around. The short of it, pun intended, all grounds in a facility MUST BE COMMON and made irreversible and fool proof by code. Both your AC and DC systems meet at some point and frequently occupy the same space. Thi smeans the is a very high chance one system can make accidental or intentional contact with each other. If the two systems are not bonded intentionally together and made common, an extreme potential of difference will exist. In order for the fuses, breaker, and GFD to operate properly must have a path to return a Shorted Fault back to the source. Example if the Utility AC power comes into contact with the DC system, and no common Fault Path is provided, the fuses, breakers, and GFD would not operate leaving hot AC power on all the surfaces for you to touch and come into contact with.

ZAP, you just electrocuted. Had you had the required bond, fault current would have flown back to the utility source and operated the breaker clearing the fault. It would also take down the DC side telling you have a problem to fix, rather than discovering by being electrocuted and equipment damage on top of it.

The AHJ knows this and if he caught it would fail your inspection. Thus why I said not going to happen for your own protection and safety. i am a pro and covering your butt just like the AHJ. Call us SOB's but we have your best interest at hand. That is what we get paid to do, and liable for our work. You on the other hand do not know what you need to know, and if you screw up is all on you. No one to sue if you get hurt, or no one for your survivors to sue if you get killed.

[sensij]

i'm not refuting what you say or arguing with you, but in the below article on pv system ground faults, how does the last paragraph on the page relate to what you say? it seems that the author is saying the pv ground should NOT be carried into the inverter. this is for a grounded pv system (i assume the author is referring to using a transformer inverter).

This quote? It explains why you can't ground a system conductor anywhere *except* inside the inverter.

Ground faults can also be introduced by wiring errors. If the grounded dc current-carrying conductor in a grid-direct PV system is connected to ground outside the inverter - at the dc service disconnect, for example - this will activate the GFDI protection system, and the inverter will shut down indicating a ground fault. Similarly, some off-the-shelf dc monitoring equipment has one of the current-carrying conductors connected to ground. If this equipment is installed in a PV monitoring system, the GFPD will see it as a ground fault. When some transient voltage surge suppressors and lightning arrestors are wired in series with one of the dc conductors, the GFPD may recognize these as ground faults as well.

[Jest Waitn]

That is not going to happen, so forget about it. It is required by code, and it would be extremely dangerous if you did not. additionally it can wreak havoc on your electrical system. To the point your TV and electronics would not work. So just get that idea out of your head as it is Best Practice.

i'm not refuting what you say or arguing with you, but in the below article on pv system ground faults, how does the last paragraph on the page relate to what you say? it seems that the author is saying the pv ground should NOT be carried into the inverter. this is for a grounded pv system (i assume the author is referring to using a transformer inverter).

http://solarprofessional.com/articles/operations-maintenance/pv-system-ground-faults/page/0/2#.WSXmMHUrJpR

[Jest Waitn]

A Renvu deal?

that is one place. how would you add the AFCI?

[adoublee]

A Renvu deal?

[Jest Waitn]

are you required to meet NEC 2014?
or rapid shutdown?

i live in florida and am told it is still under 2011 nec.

the first pv system build uses micro-inverters. i don't want to use them again. i just found 'a deal' on these 2011 nec transformer strings & am asking for input on using them. since they support both GFCI & AFCI, it seems like 'a deal'?

[Jest Waitn]

are you required to meet NEC 2014?
or rapid shutdown?

Also are you sure it has AFCI and not just GFCI?

i contacted the vendor on this matter. the standard panel supports GFCI and these have AFCI update.

[Sunking]

it seems that some say the grounds (a/c and d/c) can be connected (in common), but this really bothers me. it seems 'bad practice' to have a hot dc potential sitting on ground shared by a/c circuitry.before buying a transformer inverter, i would want to make certain the AHJ will approve separate grounding (a/c and d/c separate).

That is not going to happen, so forget about it. It is required by code, and it would be extremely dangerous if you did not. additionally it can wreak havoc on your electrical system. To the point your TV and electronics would not work. So just get that idea out of your head as it is Best Practice.

[Jest Waitn]

Transformerless are not near as robust and good as ole Boat Anchor Transformers. With a Transformer you have Galvanic Isolation which can save your home and life. Each has pros and cons.

i appreciate the honest remarks. most say the transformerless are better. but the grid operates using transformers...

the only thing i don't like about the transformer inverter design is the grounding of the pv modules (+dc or -dc) to ground.

it seems that some say the grounds (a/c and d/c) can be connected (in common), but this really bothers me. it seems 'bad practice' to have a hot dc potential sitting on ground shared by a/c circuitry.

before buying a transformer inverter, i would want to make certain the AHJ will approve separate grounding (a/c and d/c separate).

[Jest Waitn]

are you required to meet NEC 2014?
or rapid shutdown?

Also are you sure it has AFCI and not just GFCI?

this is a frame mounted pv array, not roof. grid power taken from sub-panel circa 1990 wiring (3 wires). given the configuration, it must be 2011.

the panel might support both. i checked the manual and saw the replacement of the gfci fuse in the panel. the advertising shows afci. it meets 2011 nec.

the consideration of transformer inverter is for the second array to be finished next year & the third array in 2019.

[Sunking]

Transformerless are not near as robust and good as ole Boat Anchor Transformers. With a Transformer you have Galvanic Isolation which can save your home and life. Each has pros and cons.

[ButchDeal]

it meets nec 2011.

are you required to meet NEC 2014?
or rapid shutdown?

Also are you sure it has AFCI and not just GFCI?