The right inverter for battery storage and some other Qs

[Oldgreybeard]

I think it's working fine now. The issue was the mode I was using Timing mode instead of Time-of-use with effective date being the whole year. It's a bit tricky because it doesn't explicitly say that it will feed the grid.

That's good news.

You're right, it is time of use mode that's needed to charge during the off-peak rate and discharge during the peak rate. Interpreting what the menu settings actually do isn't as clear as it could be, IMHO. Took me some time to sort out exactly what our inverter did for each setting option, and I now have a printed crib sheet by the inverter in case I ever need to set the thing up again.

[ducabi]

Now when everything is working I want to understand what's wrong in general starting with the new mini CU.

1) The spec was to include RCD + MCB curve C. Am i right that there is no RCD at all and MCB is actually curve B?
What are my options? Adding RCD + replacing MCB with curve C or do i need RCBO? I guess I need RCD not only for inverter but for lights and socket as well.

2)

Easy to fix, the MCB (circled in red below) just needs to be swapped for an RCBO (at the same time the cable rating needs to be checked - 32A is too high to protect any cable under 4mm²):

Shall I check what cables I have or change RCBO/MCB for a different one?

3) If there are so many safety issues related to it shall i report it somewhere?

[Oldgreybeard]

Now when everything is working I want to understand what's wrong in general starting with the new mini CU.

1) The spec was to include RCD + MCB curve C. Am i right that there is no RCD at all and MCB is actually curve B?
What are my options? Adding RCD + replacing MCB with curve C or do i need RCBO? I guess I need RCD not only for inverter but for lights and socket as well.

2)

Easy to fix, the MCB (circled in red below) just needs to be swapped for an RCBO (at the same time the cable rating needs to be checked - 32A is too high to protect any cable under 4mm²):

Shall I check what cables I have or change RCBO/MCB for a different one?

3) If there are so many safety issues related to it shall i report it somewhere?

You could try and report it to whichever part P body the electrician is a member of, but TBH I'm not convinced that's the best route to go down. They would almost certainly just get the electrician that did the work to try and put it right, and if I'm honest I would be concerned that this still may not make things safe. As there are obvious major safety issue visible from the photos, who knows what else might be lurking unseen? For example, are the terminals all torqued up correctly, or was the installation properly safety tested?

A B curve over current device is fine for an inverter, safer than a C curve, really. C curve devices are very slow to operate when overloaded and are intended for protection for things that have a very high initial current demand, like big electric motors and pumps, so they won't nuisance trip if there is an overload for a few seconds.

You are right, there is no RCD protection at all on the inverter circuit, it's been connected via that 32A MCB to the incoming supply at the main switch.

Swapping the MCB for an RCBO is very quick and easy and a suitable Fusebox RCBO is around £16, so not that expensive. It's a ten minute job to swap this and test it.

The lights and sockets have RCBOs already, so have RCD protection.

The cable size needs to be checked, specifically the cable running to the inverter. The cable size determines the over current protection requirement. 1.5mm² flex can carry 16A maximum, so needs a 16A RCBO, 2.5mm² flex can carry 25A, so needs a 20A RCBO. 4mm² flex can carry 32A, so needs a 32A RCBO. I doubt 4mm² flex will actually fit the terminals in the inverter, though, so I doubt that's what's been used.

The consumer unit needs two blanks fitting at the left to block the hole and prevent anyone being able to poke a finger in and touch the live busbar at the bottom. Very quick and easy to fix, and cheap.

[dangermouse]

A DC switch isn't essential, as the batteries do have switches to turn them off, but DC fuses are needed and it makes sense (IMHO) to combine the fuse requirement with a switch, as discussed earlier. The "Frankenstein" switches that include two blade fuses are a good option, as they provide both functions in one unit.

Following this thread with interest, I've just started my own install and I haven't yet got a switch/fuse between battery and inverter. I suppose a DC MCB (non-polarized) would probably be even better, although more expensive?

Have you a link to one of these "frankenstein" switches please?

So far I've found fused switches like this.

Or DC MCBs that would need to be mounted in an enclosure, like this. Although a single pole MCB would presumably be sufficient?

[Oldgreybeard]

A DC switch isn't essential, as the batteries do have switches to turn them off, but DC fuses are needed and it makes sense (IMHO) to combine the fuse requirement with a switch, as discussed earlier. The "Frankenstein" switches that include two blade fuses are a good option, as they provide both functions in one unit.

Following this thread with interest, I've just started my own install and I haven't yet got a switch/fuse between battery and inverter. I suppose a DC MCB would probably be even better, although more expensive?

Have you a link to one of these "frankenstein" switches please?

So far I've found fused switches like this.

Or DC MCBs that would need to be mounted in an enclosure, like this. Although a single pole MCB would presumably be sufficient?

I fitted the two pole version of the switch, just because I believe that both the DC cables need fuse protection. Not much more expensive than the single pole version, either: https://www.bimblesolar.com/extras/dc-f ... nect-2pole

I fitted 100A NH000 fuses to that switch: https://www.bimblesolar.com/index.php?r ... ct_id=1890

Not sure about using a DC circuit breaker. Should be OK, but I rather like being able to see the air gap when the Mersen switch fuse is open, so I know that the battery is truly isolated.

[dangermouse]

Not sure about using a DC circuit breaker. Should be OK, but I rather like being able to see the air gap when the Mersen switch fuse is open, so I know that the battery is truly isolated.

I've been reading around the topic a bit, and using a DC MCB seems to be contentious - you have to be absolutely sure you use a non-polarized one otherwise they catch fire nicely if you switch them off with the current flowing in the wrong direction! And of course between the inverter and the battery, the current can flow either way (charge and discharge).

A fuse seems to be the simpler and less risky option.

[Stinsy]

Following this thread with interest, I've just started my own install and I haven't yet got a switch/fuse between battery and inverter. I suppose a DC MCB (non-polarized) would probably be even better, although more expensive?

Don't fall into the trap of thinking that MCBs are better than fuses. They're not!

Sure an MCB is a convenient package, they are easily resettable, and also function as a switch. However there are situations where they fail, welding themselves closed as they do so. Whereas a fuse can be relied upon to do its job. High current DC is astonishingly hard to break, it REALLY wants to weld contacts together.

If you want to use DC-rated MCBs on your solar strings, go ahead. You cannot reasonably expect the rated breaking current of the MCB to be overwhelmed.

Batteries are a whole other KoF.

The internal resistance of a single string of batteries could be 0.1mΩ. A 15s 3.2V gives 48V which means the batteries themselves have a short-circuit current of 480kA (Those insulated spanners suddenly don't seem as expensive!). A typical DC-rated MCB has a 6kA breaking capacity so basically has zero chance of functioning as an overcurrent protective device (still works as a switch though).

[dangermouse]

All advice taken gratefully, I've ordered one of those fused switches from Bimble.

[dangermouse]

Talking of Current Transformers (a few pages back) I'm trying to find a neat way to fit mine...

Does it matter if the CT is loose on the cable? Should I wrap a bit of tape around the cable to pad it out for a snug fit?

Also, does it matter if the neutral cable is touching the outside of the CT?

[Oldgreybeard]

Talking of Current Transformers (a few pages back) I'm trying to find a neat way to fit mine...

Does it matter if the CT is loose on the cable? Should I wrap a bit of tape around the cable to pad it out for a snug fit?

Also, does it matter if the neutral cable is touching the outside of the CT?

None of those things matter at all, CTs are pretty much immune to interference etc. Only thing that does upset them is if they aren't clipped on fully, any tiny gap between the two halves of the ferrite core can cause them to misread.