Trying to make my DIY setup as safe as possible

meetyg

New Member
Hi there.
I have a small (but a bit complicated) grid-tie DIY solar setup.
I have been playing around with solar a bit, just to learn, but now am trying to make my DIY setup as safe as possible, given some constraints.

Basically I am using those cheap no-name Chinese micro-inverters (I have two, one is a GTB-600W and the other is a GTB-1200W).
They both have anti-islanding, and will only produce AC power if the grid is live.
Other than that their specs are fairly unknown/unclear to me...

I have two 450w glass panels connected to the GTB-1200, and four 100w flexible panels connected to the GTB-600.

The micro inverters are connected to an AC wall socket. Yes, I know that this is not ideal, but please don't criticize me for this. I really have no other choice, as my main AC panel is far away, and I would have to drill holes in concrete to get a line straight to the main panel. I'm also trying to keep this setup as cheap as possible, in order to make it cost effective and offset some if my electrical bill.
But I am willing to invest a little in some safety measures.

The micro inverters are not installed under the panels (although they are IP65 rated) but rather placed in a box (with fans for cooling) about 5 meters away from the panels.
The reason for this is to increase the life of the inverters, making them run cooler and not exposed to the elements.

Anyways, I'm pretty confused as how to make this as safe as possible. Currently I only have a DC isolator switch between the panels and the micro inverters, and a 16A MCB between the inverters and the AC socket.

After lots of reading online I have some questions, as there are mixed statements around:
1. Grounding:
Do I need to ground the inverters?
Both of them have a ground hole on their metallic casing. But from doing a continuity test, it seems both do NOT have continuity from the DC terminals to the metallic housing.
One of them (only the GTB-1200) has continuity from the housing to the AC ground wire.
Does this mean that the GTB-1200 is DC isolated and does not need additional grounding?
Can I just bond the GTB-600 to the GTB-1200 so that it will also be grounded?

Also, is it safe to ground the PV panels (frames and rails) to the AC ground wire coming from the wall socket (just like the GTB-1200 does), or do I need a dedicated ground wire and grounding rod for the panels ?

2. Fuses, MCBs and SPDs:
DC SIDE:
Assuming I get proper grounding sorted out as above, do I really need fuses and MCBs between my panels and the micro-inverters ?
Will this help protect my micro-inverters or is this redundant? (they have no external fuses on them).
Should I also use an SPD on the DC side?
If so, again how should I ground it properly?

AC SIDE:
Should I install an RCD between the inverters and the wall socket?
I am trying to protect the line and other loads (wall sockets, lights, etc...) and of course people in the house from possible short-circuits, ground/isolation faults.

If I need an RCD, how many milli-amps should it be rated for, given that the main RCD is rated 30ma (type AC).
I have read that it is recommended to get a 100ma RCD for some installations, but they were for a direct line, not a wall socket connection like mine is.
From my understanding, the danger here is that if a fault should occur, the main RCD could trip, but the micro inverter might still supply AC current to the line, untill it detects the the grid is disconnected (could take a few seconds I suppose). This means that someone could still get electrocuted until the micro inverter responds and cuts out the AC current it's producing.
Am I correct?

Sorry for the lengthy post, and thanks in advance for your answers and advice.

Just one last thing, as for local code and regulations, I am aware that my setup might be in the grey area of legality/regulations.
But, as I have seen similar setups being done by companies such as Legion Solar I guess that it might not be that bad.
They don't really explain how you should handle all these issues, so I am.just trying to do my best to understand and make my setup as safe as possible...
 

meetyg

New Member
BTW, I forgot to state that the maximum DC voltage if this setup will be less than 50v DC.
My household AC is single phase 240v AC.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
My household AC is single phase 240v AC.
HANG ON !
North America: 240VAC SPLIT Phase @ 60Hz
Europe: 210-230VAC SINGLE Phase @ 50Hz (pending on Grid System)
These are NOT compatible and cannot be interchanged.
If you attempt to use a 230/240VAC Single Phase in North America and you plug in a 240V/60hz Split phase appliance into that you will get a Huge POOF !

There is ABSOLUTELY NO ROOM for Guessing on this. Wrong Guess CAN kill you while burning down your house at the same time.

Also, PV Panels are NOT to be grounded to an Electrical Ground Point. They (frames & rails) need to be Earth Grounded for Lightning & Spike safety. The + & - off the solar panels is separate and is obviously electrical. Negative is NOT ground on a panel either...

SPD's (Surge Protection Devices) should also be on the incoming DC from the panels & on the AC Panel going out from Inverter system. With micro-Inverters I am not sure how that works. AC & DC SPD's are NOT interchangeable.
 

meetyg

New Member
OK, I'm understanding that I need an SPD, but where should I earth it? Should it just be and additional ground rod, or should I try to get to the building's ground connection?
Can the panels and the DC SPD be connected together?
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
I'm obviously in Canada and so our rules/codes may not be the same with regards to the setup and I am not familiar with Micro-inverter configurations. I deal with central Inverter systems with Solar Charge Controllers which is quite different.

With regards to the "panels & rails" assuming the panels are mounted to a rail system, the panel frames need to be bonded to the rails (some require a wire, other will allow for the clamps to do so) and the frames-rails are grounded to an Earth ground spike or buried grounding plate with 6 or 8 gauge "green" jacketed wire. Green jacket is to clearly indicate it is a Ground wire. There is no SPD required for that. If the panels are Roof Mounted but without rails, then they need to be bonded together with a running ground wire using the appropriate ground lugs for the panels.

Again, ALWAYS defer to your local Codes, Rules & Regs because they exist for good reason. Also if it is to be inspected or for Insurance purposes (they love any excuse to deny claims) you want everything to meet the codes.
 

meetyg

New Member
OK, so after researching some more, I have found out that my intentions to make it safe this way would be even more complicated.
Not only RCD issues, but also branch protection issues too.

Now I'm asking what would be the ideal way to connect the inverter to the main panel?
Although at first I thought it would be impossible to get to the main panel, but I have some ideas, but before that I want to understand fully how to do it right.

I have read that it should go to a dedicated breaker (MCB) at the main panel, but where should that breaker be in regards to the main MCB and RCD in the panel?
Should it have its own RCD? If so where?
I'm kinda confused.

Thanks
 
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meetyg

New Member
One if my ideas is to get to the RCBO I have for my EV Charger.
This RCBO is placed next to the main panel, inside the house. It gets its power from the main MCB of the AC supply panel in my house (skipping the main RCD).

From this RCBO runs a dedicated AC line to the EV charger.

I just might be able to run a new AC line in the existing conduit the runs the charger line from inside to outside the house. I just need to check how much free space there is in the existing conduit to run another line (if at all).

The question is, let's say it's feasible, would it be a good idea? Also, where should it connect to in regards to the RCBO (input side, or output side)?

The RCBO is a Hager RCBO (20A, type A, 30ma), and as I have read in some other forums, most HAGER RCDs are bi-directional so that (supposedly) shouldn't be a problem.

What do you guys think?
In case of a fault, would it risk the EV charger and/or EV?
Would I need anything else (additional MCB maybe)?

It would be nice that some of the EV charging would be offset by the inverter, but I mainly charge at night anyways, and I would like most of the AC generated just to go to the AC consumers of the house.
 
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