How much can I practically/legally DIY, and other newb questions

[dangermouse]

OK sorry to bang on about this ... my confusion is because several posts have previously recommended using a 100mA RCD, and that's what the inverter manual says:



eg: here.

Requiring a 30mA device may make things easier for me, as 100mA devices for my aging consumer unit are hard to find. It's a "Square D" brand, approx 20 yrs old - but I think Schneider

The existing RCD in my CU (that protects the house circuits) is type AC, I suspect that 20 years ago, type A didn't exist or at least wasn't commonly used. As it's a reasonably old installation, there's a single RCD feeding a bank of MCBs.

So, if I've understood everything correctly, I need a C25 Type A 30mA RCBO (I initially estimated a 32A breaker but the inverter manual says use 25A). And if I can get one of those that fits, I'll pop it in the spare way in the CU, connect to the inverter (via isolator) and that's it.

If I can't get one of those RCBOs to fit my CU, I'll add a C25 MCB to the spare way, and connect that to an electric shower (or similar) CU containing the required RCD, and then on to the inverter.

[Oldgreybeard]

I think inverter manuals often don't seem to take account of wiring regulations here, nor does the hardware at times. As an example, the wiring glands on our Sofar ME3000SP are non-compliant with the wiring regs. If used as supplied they would result in single insulated wires coming through the cable glands and being able to be touched, which is a serious breach of the UK regs. Easy to swap the glands for standard ones that allow a suitable double insulated cable to be used, but there is no mention in the manual of the need to do this to comply with UK regs.

Same goes for things like RCD protection, and you will find it hard to buy a 25A device, as the normal rating steps in the UK are 6A, 10A, 16A, 20A, 32A, 40A and 63A. I don't believe the inverter manufacturers can make their manuals detail every different countries regulatory requirements so it's probably best to use the manual as guidance and defer to the wiring regs when it comes to the definitive and safe way to wire the unit up.

[dangermouse]

Same goes for things like RCD protection, and you will find it hard to buy a 25A device, as the normal rating steps in the UK are 6A, 10A, 16A, 20A, 32A, 40A and 63A.

Yes, I've noticed this, 32A it is then. Thanks for the tip about the glands too. I've got a Sofar inverter on order so I'll make sure I check that.

I think I've finally found the right RCBO for the job: https://www.cef.co.uk/catalogue/product ... -30ma-rcbo

[Oldgreybeard]

Same goes for things like RCD protection, and you will find it hard to buy a 25A device, as the normal rating steps in the UK are 6A, 10A, 16A, 20A, 32A, 40A and 63A.

Yes, I've noticed this, 32A it is then. Thanks for the tip about the glands too. I've got a Sofar inverter on order so I'll make sure I check that.

I think I've finally found the right RCBO for the job: https://www.cef.co.uk/catalogue/product ... -30ma-rcbo

That RCBO looks fine to me. The bit about the glands on the Sofar is shown in this diagram from the manual for ours:

Sofar glands.jpg (47.06 KiB) Viewed 3217 times

The glands each have three holes in the rubber insert, so that three single wires can come through, which would leave three single insulated wires hanging under the unit. The fix is to either swap the glands completely (they are standard M20 hole nylon glands) or just swap the rubber insert for one that has a hole that will take double insulated cable. I wired mine using some 2.5mm² three core SYY cable that I happened to have lying around, OK as my inverter is indoors (SYY isn't rated for outdoor use). The cable ideally needs to be flex, as it's a bit tight getting rigid cable in there (I initially tried to use some 2.5mm² NYY-J but it was just too difficult to dress into the limited space).

Sofar cables.jpg (56.14 KiB) Viewed 3217 times

[dangermouse]

That RCBO looks fine to me. The bit about the glands on the Sofar is shown in this diagram from the manual for ours:

Exactly the same diagram in the manual for the HYD-3600, which is the one I'm getting.

The glands each have three holes in the rubber insert, so that three single wires can come through, which would leave three single insulated wires hanging under the unit. The fix is to either swap the glands completely (they are standard M20 hole nylon glands) or just swap the rubber insert for one that has a hole that will take double insulated cable. I wired mine using some 2.5mm² three core SYY cable that I happened to have lying around, OK as my inverter is indoors (SYY isn't rated for outdoor use). The cable ideally needs to be flex, as it's a bit tight getting rigid cable in there (I initially tried to use some 2.5mm² NYY-J but it was just too difficult to dress into the limited space).

I'm mounting indoors too - I had also considered the NYY-J cable but I was concerned about the flexibility, so thanks for that tip too. CEF do some rubber sheathed flexible HO7RNF which seems more than adequate.

[Oldgreybeard]

If your inverter is rated at 3kW, then you may find that 4mm­² cable is too big to fit the glands and terminals that easily. You will have to use 4mm² if using a 32A RCBO, as that's too high a current rating to protect 2.5mm² cable. Largest size RCBO that can be used to protect 2.5mm² cable is 20A.

[dangermouse]

If your inverter is rated at 3kW, then you may find that 4mm­² cable is too big to fit the glands and terminals that easily. You will have to use 4mm² if using a 32A RCBO, as that's too high a current rating to protect 2.5mm² cable. Largest size RCBO that can be used to protect 2.5mm² cable is 20A.

Inverter is 3.6kW. Good point on the cable - 2.5mm² should be good for 32A in free air but it's a bit borderline (going on info from http://www.cable-ratings.co.uk/).

Luckily, cable is cheap, and I only need a couple of metres, so if the 4mm² cable won't go into the inverter, I'll have to go for 2.5 and get a 20A RCBO. It would be an expensive mistake though to pick an RCBO with too low a rating, and find it trips out whenever the inverter ramps up. Although, being curve C makes that unlikely, you would hope.

[Oldgreybeard]

If your inverter is rated at 3kW, then you may find that 4mm­² cable is too big to fit the glands and terminals that easily. You will have to use 4mm² if using a 32A RCBO, as that's too high a current rating to protect 2.5mm² cable. Largest size RCBO that can be used to protect 2.5mm² cable is 20A.

Inverter is 3.6kW. Good point on the cable - 2.5mm² should be good for 32A in free air but it's a bit borderline (going on info from http://www.cable-ratings.co.uk/).

Luckily, cable is cheap, and I only need a couple of metres, so if the 4mm² cable won't go into the inverter, I'll have to go for 2.5 and get a 20A RCBO. It would be an expensive mistake though to pick an RCBO with too low a rating, and find it trips out whenever the inverter ramps up. Although, being curve C makes that unlikely, you would hope.

The cable rating table you need to use is the one in the wiring regs, that rates 2.5mm² flex cable at an absolute maximum of 25A for single phase, 4mm² flex is rated at 32A maximum:

Flex cable rating from the regs.jpg (59.29 KiB) Viewed 3160 times

Our Sofar is connected using a 20A RCBO, which is fine, as the maximum current normally (for 3kW) is slightly over 13A. A 3.6kW inverter could draw or supply about 15.6A, so still fine on a 20A RCBO.

[dangermouse]

OGB you are a constant source of useful info, thanks again.

[Oldgreybeard]

OGB you are a constant source of useful info, thanks again.

You're welcome, I had to sort all this stuff out when I installed our battery system, getting on for two years ago now. Lots of potential gotchas I found, not least because there was all sorts of conflicting advice around.

The last wiring changes I made, when enabling the emergency backup power system, posed the most problems in terms of finding out what was needed to be safe and comply with the regs. That was also the hardest in terms of coming up with a neat way to run the cables. I ended up running conduit and using single wires inside it, made life a great deal easier, just one run of conduit has now got the grid supply, the EPS supply, plus the wiring from our second PV inverter.

I'd not used singles and conduit before, but have to say it made for a very neat and tidy way to fit what would otherwise have been a bit of a rats nest of cables. It was also a lot quicker to install, as pulling single wires through conduit was very easy when compared with running three runs of cable clipped to an outside wall.