Question about install - cable size between inverter and consumer unit

[KentPV]

I've just had a new solar installation and I've got a question about the size of cable used by the installer. I've got a 14 panel system and a Solis inverter (RHI-3.6K-48ES-5G).

The cable used is twin and earth 2.5mm and I've noticed it runs quite warm when the system is in full operation. Note that my loft also gets extremely hot and it is always warmer than outside, so it would have been well in excess of 40 degrees in the recent hot days.

The cable is about 8m long, the inverter is in the loft and the cable feeds through to the consumer unit in the house down a channel cut into the wall and plastered over.

Is the cable undersized? Is it good practice to fit a cable that heats up? Thoughts appreciated.

 

[Wjm1964]

Cables do & can get warm. As long as its fused correctly it should be fine. That's why we use Fuses, you want that to blow before the cable over heats. If my memory serves me correctly 2.5mm is rated for about 20-24 amps. Being in the wall as opposed to the outside e.g in a conduit it will hold heat if that makes sense as it can't dissipate quickly. You can always use higher rated cable if it gives additional peace of mind.

 

[KentPV]

Thanks.

I've done a bit of electrical work round the house, for example adding a fused spur or adding an extra socket on a ring main. I've always steered well clear of the Consumer Unit though.

I know it is probably within standard, but just doesn't seem right the electrician spec'ed a wire that heats up. A 4mm2 wire would only have been another tenner.

 

[SeaGal]

I know it is probably within standard, but just doesn't seem right the electrician spec'ed a wire that heats up. A 4mm2 wire would only have been another tenner.

Technically within spec, but poor practice IMHO. 8m is not that long, but you will lose about 30W and have voltage rise of nearly 2V for 16A. Far better would have been 6mm2. See https://photovoltaic-software.com/solar-tools/voltage-drop-calculator-dc-ac to check different sizes.

I installed 8mm2 on mine, though the Solis is much further from the CU than yours is.

 

[KentPV]

Thanks.

I believe it is very poor practice. The wire gets quite warm when under load and I don't believe the electrician took into account that the cable has been plastered into the wall going down to the Consumer Unit (which I told him I would do). In the recent 40 degree heat my loft where the inverter is installed would have been at least 10 degrees warmer which puts the cable right at the very limit of spec and likely overloaded.

The installation is now subject to a complaint because although (just) within specification the inverter AC capacity is too low relative to the potential PV output resulting in constant clipping.

 

[12VoltInstalls]

As long as its fused correctly it should be fine. That's why we use Fuses, you want that to blow before the cable over heats

But the cable should be big enough to not got hot in normal use. There are charts (well actually formulas) on this

 

[FVScimitar]

You will get clipping with G98 3.6kW inverter with 14 panels approx 5.2kW array... re-apply to DNO G99 for larger inverter.
if you do the existing cable will not cut it, 6mm2 twin& earth