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binky

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The points made about PV not sharing a RCD caused me to checkout our PV, installed 10 years ago.

The Wylex plug-in-fuse CU is fed from an external 100A 30mA RCD.

The inverter AC output is fed to the CU via 2.5mm2 to a Wylex plug-in 30A MCB the installers added.

Shouldn't that be more like a 16A MCB, to protect the cable ?

There are suitable rotary breakers between the PV DC and the inverter, between the inverter and the FIT meter, and between the FIT meter and the 30A RCD in the CU.

Though there is one unplugged hole and no glands on some of the breaker cable entries.

If only I know then what I've learned from this forum.......
the classic update by adding a single external RCD for the entire board - no longer acceptable due to 'nuisnace tripping' ie a single fault wipes out the entire house elecrical supply.

30A is too large for a 2.5mm cable, which is rated at 26Amps maximum. I would fit 20Amp so that it's not pushing the mcb to it's limits.

Holes in board / isolators contravene 'ingress protection' and allow finger insertion - rough work.

To be frank, if you have the old plug in MCBs it may well be worth considering a full EICR (inspection and test) and getting the board updated. The one good thing about single RCDs is that you almost certainly havn't got any major issues with cabling / appliances, or it would keep tripping out.
 

Andy1733

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The points made about PV not sharing a RCD caused me to checkout our PV, installed 10 years ago.

The Wylex plug-in-fuse CU is fed from an external 100A 30mA RCD.

The inverter AC output is fed to the CU via 2.5mm2 to a Wylex plug-in 30A MCB the installers added.

Shouldn't that be more like a 16A MCB, to protect the cable ?

There are suitable rotary breakers between the PV DC and the inverter, between the inverter and the FIT meter, and between the FIT meter and the 30A RCD in the CU.

Though there is one unplugged hole and no glands on some of the breaker cable entries.

If only I know then what I've learned from this forum.......
I'm no electrition though I've been property developing for several years so have been around electrical insulation
I'm sure 2.5mm cable is rated to about 25a max. so the MCB needs to be lower. I believe most ring mains go on a 16a

I'm sure someone on the know will confirm the correct breaker
 

binky

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Sorry Binky your post wasn't showing up when I wrote my reply ☹️.
No problem, but please leave the electrics to sparkies 😄

Ring mains can be rated at 32amps, we use 16amp and 20 amp MCBs for radial ccts. Personally I like radial ccts, as its much harder for DiYers to mess them up. I only install ring mains these days in high demand areas like a kitchen/ utility area.

How's the world of property development going these days?
 

Andy1733

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No problem, but please leave the electrics to sparkies 😄

Ring mains can be rated at 32amps, we use 16amp and 20 amp MCBs for radial ccts. Personally I like radial ccts, as its much harder for DiYers to mess them up. I only install ring mains these days in high demand areas like a kitchen/ utility area.

How's the world of property development going these days?
A bit of a pig. I've been no stop upto November last year and I said fk it time for a break. I planned on having 3 month off then booom. Housing market went mental. I've got one in the pipe line. Just a 2 up 2 down which I intend keeping. Fingers. Crossed it will be completed by end of this month though it's been in the pipe line for last 4 month 😁
 

Andy1733

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Tbh I've not been sat idle.
I've been helping the sparky who fitted my solar. A friend of a friend's son bought a house and got a "hand over eyes" builder. He's smashed the house to bits. Squeezed 30k out of them then done a runner. He, (sparky) asked me if I would take a look and asses what they can do to make it livable.

Omg. I've never seen a house in such a state. Old builder had tanked 2 of the 3 external walls in the extension. I say tanked he did patched to about 3 foot high. Double boarded over to hide what he had done (mold already coming through) he then Skimmed then fitted the kitchen. The base units he fitted sloped from left to right and then he tiled using the worktop as the level. He hadn't even done the first fix of electrical/plumbing.

There were open end live cables hidden behind the plaster. The list is endless.
We just said. Look whilst were not busy, we can give you 3 weeks. You pay for parts and we will install them for free. So we removed everything cable related. Chased in the first fix and sparky was buttoning up whilst I rebuilt them a wall that was dangerously leaning at the top of the stairs the bricked up the old back door. Plumber came in this week and got all the first fix in for them.
So basically the foundations are in place. It just needs the plasterer to come in and smarten the rooms and a joiner to fit the timber work.
 
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you want to be feeding energy to the 'grid side' of the RCDs and MCBs, so Live and neutral are 'upstrem of the RCDs. That way if the RCD trips coz you stuck a wet finger in a socket (please don't try doing that) it isolates you from the solar energy - the RCDs are twin pole and isolate Live and Neutral when tripped.

The solar and battery will need their own MCB - there's some debate about RCDing such ccts, under the new regs update we are suppossed to RCD (or use an RCBO to combine RCD and MCB protection into a single spare way) every circuit. Personally I think that is uneccessary as you can't plug any appliances into that cct , and it's acceptable to 'risk assess' a cct for RCD requirement. Solar inverters tend to have RCD protection for the AC side built in anyway. I also don't like RCD protection on fridges and freezers, so if doing a full rewire, I supply them with a dedicated cct - for some strange reason Freezers like to trip RCDs whilst you are on holiday!
Ah yeah. That all makes sense. Thank you.
Looking at my CU then. How would the electrician feed neutral and positive to the grid side whilst maintaining mcb protection. Is it acceptable to trim the common positive feed to the solar and battery mcbs and run some cable between them and the grid feed?
 

Gian

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A spare slot in your consumer unit,?
Make sure it doesn't share an RCD with any other circuits
Some inverters manufacturers recommend using not a 30ma but 100ma worth checking . Specially older versions . In which case you would prob need to add a another cu for that new circuit.
 
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Some inverters manufacturers recommend using not a 30ma but 100ma worth checking . Specially older versions . In which case you would prob need to add a another cu for that new circuit.
Will check with Solis. Cheers for the heads up. (y)
Though if my CU is rearranged there will be no RCD other than the inbuilt ones.
 

BorisJ

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Ah yeah. That all makes sense. Thank you.
Looking at my CU then. How would the electrician feed neutral and positive to the grid side whilst maintaining mcb protection. Is it acceptable to trim the common positive feed to the solar and battery mcbs and run some cable between them and the grid feed?
There is no positive. It is AC.
 

glenns

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The inverter needs grid and backup cable. So will I need 2 mcbs for that alone? In which case a mini CU will be needed.
Also recommended 6mm2 cable seems a bit heavy duty for 3kw?
You don't have to use the backup, that's just if you want to run a cct for when the grid goes down...as for the cable sizes they are a bit beefy in the schematic but I'm guessing they have done that to cover all bases...you need to use what's suitable for your installation.
 
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You don't have to use the backup, that's just if you want to run a cct for when the grid goes down...as for the cable sizes they are a bit beefy in the schematic but I'm guessing they have done that to cover all bases...you need to use what's suitable for your installation.
Good. That's a relief.:).
Western Power specify that islanding is not allowed if I remember rightly, so I wasn't planning to use that anyway.
Do I have to use SWA as the setup is going to be indoors?
The manual for this 3kw inverter specifies 6-12mm cable which seems overkill if the inverter is only 3 or 4m away from the CU. 6mm it is then. 16A MCB?
 
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binky

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Good. That's a relief.:).
Western Power specify that islanding is not allowed if I remember rightly, so I wasn't planning to use that anyway.
Do I have to use SWA as the setup is going to be indoors?
The manual for this 3kw inverter specifies 6-12mm cable which seems overkill if the inverter is only 3 or 4m away from the CU. 6mm it is then. 16A MCB?
I would use at least 20A MCB, but if you are cabling in 6mm then you could install a 32A. I would use 4mm or 6mm flex, HR07NR or heat resistant flex, or HiTuff, or you could use a short length of flex and 6mm Flat twin and earth (normal domestic cable). It most certainly doesnt need to be swa indoors.
 
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Ah yeah. That all makes sense. Thank you.
Looking at my CU then. How would the electrician feed neutral and positive to the grid side whilst maintaining mcb protection. Is it acceptable to trim the common positive feed to the solar and battery mcbs and run some cable between them and the grid feed?
Is this acceptable practice for the live feed?
 

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