Cable size between inverter and consumer unit

[SUNBATH]

Hi. As we do some restauration currently I would like to add a cable from the loft to the first floor before a solar system will be installed later.

What size of cable should I use please to comply with building regulations ?
The system will have a max capacity of 3.6 kWh

thank you

 

[Phoenix]

Generally 4mm is used as the starting point for domestic PV, but has the potential to require larger; current carrying capacity on a 4mm for a 3.6kw (typo I'm guessing?) is unlikely is unlikely to be an issue, but volt drop could be depending on length, you should keep it to a minimum for the cable to a solar system, 1% for max volt drop sticks in my head, but don't know if thats specified anywhere or just considered good practice.

It can't share an RCD with anything else, best idea to to use cable type abd route that mean it doesn't require RCD, if not possible, then an RCBO on the mains switch controlled section of the board

 

[SUNBATH]

Hi. Thank you for your fast reply.


This is for the cable size of the ac cable from after the hybrid inverter to the consumer unit, right?

Thank you for the reminder with the rcd, I'm not sure they can fit it, but at least there is space for a separate consumer unit

 

[binky]

For that size inverter 2.5mm would suffice, but I would fit 6mm, as this would reduce cable losses for a little extra money, and give flexibility to add batteries at a later date. You could use 4mm, but that is often more expensive than 6mm, as it's not used as much in the electrical industry.

 

[SUNBATH]

Thank you very much both. Appreciate your help.
Do I need to get an extra earthing cable as well down from the loft for the battery?

 

[binky]

Thank you very much both. Appreciate your help.
Do I need to get an extra earthing cable as well down from the loft for the battery?

no, bond to the inverter casing.

 

[SUNBATH]

Thank you again. Last question, our main electric connection for the house is outside and the consumer unit inside under the staircase. The electrician will just need the 6mm ac cable from the hybrid inverter in the loft to the area of the current consumer unit right ? Or will he need another cable to the main outside electric connection from the loft or even from the consumer unit?

 

[binky]

If you are replacing the board, take it to that. Make sure it's on its own circuit and not sharing a RCD

 

[SUNBATH]

Thank you, so I don't need an extra cable to the outside connection from the loft, right?

I calculated that the electrician might need a separate consumer unit for the pv, exactly because of the rcd you have mentioned. But as the consumer unit is just 1 year old, maybe he can use it with not sharing the rcd?

 

[Murdoch]

Can you post a photo of your fuseboard?

 

[SUNBATH]

Sure. Great how helpful you all are, thank you very much

 

[binky]

Sure. Great how helpful you all are, thank you very much

who put a plastic board in, at 1 year old it should be metal, which has been a requirement for several years.

Looks like you have a couple of spare ways, but unless that board has a third neutral bar, it would be easier to install a mini board.

 

[Murdoch]

I think that's a metal board BUT who installs a replacement board with no spare ways

 

[SUNBATH]

It is a metal board

What do you mean with spare ways?

 

[Murdoch]

It is a metal board

What do you mean with spare ways?

Ones that are not used

 

[binky]

It is a metal board

What do you mean with spare ways?

looked like moulded plastic, my bad.

You have 2 unlabled circuits, which I am assuming are 'spares'. If they are in use, then some lazy arse should have labled what they do

 

[truffle pig]

You mention its a Hybrid inverter, so I guess you will be putting batteries in? worth putting a CAT6 cable in from incoming supply to inverter for CT clamps / monitoring

 

[michael8554]

The 2.5mm/4mm/6mm cable from the inverter to the CU allows the inverter to send current from the PV panels into the CU, to reduce the current being taken from the "outside connection".
That's all you need, no need for a cable from the CU to the "outside connection".
The breaker in position 3 with the label torn off has a 40A rating, suggesting a high-current device such as a shower was, or may still be, connected to it?
The breaker in position 7 with no label has a 30A rating, the same rating as the "Existing Sockets".
So maybe an extra set of sockets have been added since the house was built, in an added conservatory perhaps?
If you're not sure what it does, switch it off and hope nothing stops working.
Then it may be be a "spare way" you can use for the inverter.

 

[SUNBATH]

Thank you all. Yes, those two unlabeled ones are unused. I though it is normal that an unused one doesn't have a label, ha ha

So that means that the electrician can use this consumer unit and add the new 6mm cable to the inverter without the need of a second consumer unit, right? And without connecting to the rcd

@truffle pig , good thought, I have already one there luckily . But thank you.

Still I wonder if I need beside of the 6mm ac cable from the inverter to the consumer another 6mm ac cable from the hybrid inverter to the outside electric connection? I wouldn't think, but just want to make sure, as it will be a good chance now but bad in the future )

 

[Murdoch]

I would seriously advise against adding the PV to this fuseboard unless it can be reconfigured to add a rcbo before the first RCD

Reason being is that a rcd shuts off the power in max 30 ms. The PV inverter can take seconds and by then you could be dead