Are my x2 2.5sqmm cables suitable for a 5kW E/W system?

[Zenith63]

Hey guys,

Firstly just to say that the PV system is being installed by a certified company/electrician, so this query is just to satisfy my own curiousity really. Also I’m based in Ireland and I know our regs will be slightly different.

As I was slowly renovating my house I had in mind that I might put solar panels in some day. I didn’t look into it at the time (a LOT going on), but ran in two 2.5sqm flat grey T+E (the new type, with the Earth separately insulated like the live/neutral) from the attic to the fuse board. They’re probably 20m long and in the insulated stud walls/floor.

Fast forward to 2019 and the solar grant in Ireland is being reduced so I put in an order for 4.85kW of panels in an East/West setup, a 5kW dual-MPPT hybrid inverter and 4.8kWh of batteries.

I’ve been kicking myself that I didn’t do more research before putting in those 2.5sqmm runs as it will be very difficult to add more cables now (without going external etc), pulling in a 4/6/10sq would have cost feck all. Anyway, guess my question is just whether the solar company will be able to use the 2.5s or not. I guess a single 2.5sqmm would be very tight from a 5kW inverter; even though with an E/W system the panels will never generate more than maybe 3kW peak, the battery could also provide some juice and push my up to the 4.8kW limit of a 2.5sqmm cable. Can the two cables be used in parallel to come to a total of 5sqmm and in theory closer to 10kW limit, is that a thing?

Thanks for any comments, as I say more of a thought exercise than anything!

 

[Risteard]

The first thing that you should be aware of is that by running in the cables in, assuming that this was done since the 1st October 2013, you have committed a criminal offence as these are Restricted Electrical Works. (Given that you state that the new type of T&E has been used then I will assume that the cables were installed in the last two years.)

You will need to apply for a Change of Contractor from RECI for any Registered Electrical Contractor (REC) to be able to use & certify any existing wiring for which they were not responsible.

See http://www.walshelectrical.ie/electrical-services.html#restricted-works for further information regarding Restricted (Designated) Works.

 

[Devonchris]

Can the two cables be used in parallel to come to a total of 5sqmm and in theory closer to 10kW limit, is that a thing?

No. 2 x 2.5mm csa does not equal 5sq mm.

That's why people overeat, they think a 12 inch pizza is only twice the size of a 6 inch pizza. It's four times the amount.

 

[Zenith63]

No. 2 x 2.5mm csa does not equal 5sq mm.

That's why people overeat, they think a 12 inch pizza is only twice the size of a 6 inch pizza. It's four times the amount.

Maybe I have misunderstood cable sizes all this time (quite possible ), but why would two 2.5sqmm or 2.5CSA not add up to 5sqmm or 5CSA. We’re talking area here right, not diameter (how pizzas are measured)?

While checking my post to ensure I’d said 2.5sqmm not 2.5mm, I realised I actually said 2.5sqm at one point - certainly wouldn’t have an issue with 5kW down a cable that size!

The first thing that you should be aware of is that by running in the cables in, assuming that this was done since the 1st October 2013, you have committed a criminal offence as these are Restricted Electrical Works. (Given that you state that the new type of T&E has been used then I will assume that the cables were installed in the last two years.)

You will need to apply for a Change of Contractor from RECI for any Registered Electrical Contractor (REC) to be able to use & certify any existing wiring for which they were not responsible.

See http://www.walshelectrical.ie/electrical-services.html#restricted-works for further information regarding Restricted (Designated) Works.

Thanks for that, was genuinely not aware that you cannot even run in cables yourself! It was indeed done after 2013!!

 

[Devonchris]

Maybe I have misunderstood cable sizes

You are right. My error. I should pay more attention.

 

[Zenith63]

So just to satisfy my curiosity, accepting that either way the sparks will likely rip out my two cables when he comes, are parallel conductors like this a thing and allowable?

 

[Risteard]

So just to satisfy my curiosity, accepting that either way the sparks will likely rip out my two cables when he comes, are parallel conductors like this a thing and allowable?

ET101 is much stricter about where parallel conductors are permissible than BS7671 - for example they are never allowable for final circuits.

2.5mm^2 cable is a very odd size to want to parallel anyway as there would be little, if any, benefit. (Bear in mind that a ring final circuit is not a parallel circuit.)

As I suggested earlier this is a job for your REC - and indeed there are severe penalties for breaches of the law.

 

[westward10]

It is a shame the UK doesn't adopt your practices.

 

[Zenith63]

It is a shame the UK doesn't adopt your practices.

How are things different in the UK, my sense was that Ireland tended to follow the UK for much of this kind of thing?

I think it would be good for electrical distributors here to require proof of a REC cert before they’ll sell you anything that a DIYer obviously should not be touching (fuses, non-flex cable, socket/switch faces, consumer panels etc). As I said I genuinely wasn’t aware the restrictions here, I worked with my father decades ago doing some labouring on electrical jobs so it’s always just been second nature to me to run cable etc.

 

[westward10]

You might want to start another thread on that as it will get people on their soap boxes. The situation in the UK is a farce.