what can I do

[potatoman]

Hi
before installation of my PV system I specifically asked my installer to check my AC cable to the fuse box (as it is 140 meter long). He said it was ok and proceeded to fit a 4 KWP system. Now when the system produces more than 2.5 KW the invertor trips out I have been told by SMA that the resistance in the AC cable is too high. What can I do?
Potato man

 

[babba]

Get the installer back and kick his a** till its sorted.

 

[Earthstore]

Contact the installer and get him to change it, one of the experts will probably do the calcs for you to tell you what size cable is required. 10mm?
Chaps?

 

[potatoman]

Had the installer back, he wants to increase the pramiters of the inverter, the restance in the cable is 1.2 ohm,is this safe

 

[jupestar]

can't do he calcs. but last time we did a 150m run we used 90mm. it was 20kwp though.

 

[GaryM]

What type and size is the AC cable?
Also, what's the installation conditions of the cable? SWA buried in the ground I assume?

 

[Earthstore]

It has to be calculated for volt drop over a distance.

 

[Earthstore]

Or maybe the inverter has not been set to UK spec.

 

[potatoman]

set to G83

 

[Earthstore]

Sometimes the installer is not aware that the inverter has to be set for the UK voltage, even though it is G83 approved.
If you know what size the cable is I am sure GaryM would do the calcs for you, he is a good chap.

 

[jerriais]

Hi Potatoman,

I'm happy to do those calcs for you if you can tell me what panels and inverter combination you have, although I have to say any installer that doesn't even provide this most basic element of system design is not fit to be MCS accredited. How can our customers be protected from people like this if our own industry accreditation scheme doesn't weed them out of the market?

Matt

 

[nowty]

1.2 Ohms ?, at 16amps thats about 20 volts dropped, thats madness, of course its going to trip out.

If the nominal mains is say 240v then the inverter (at max power) has got to kick out 240v + 20v + several volts to get the currect to flow into the grid. Will probably be up to 270v so I am not surprised it trips out at 2.5kw (about 10 amps).

I think the voltage drop has got to be less than 3% and preferably less than 1%, so your AC cable is way undersized.


EDIT - This is of course if the 1.2 Ohms figure you quote is correct.

 

[SolarCity]

Can you see your AC cable? Can you check to see what size it is?

It sounds to me like your installer may have made a mistake. If he has not upgraded the size of the cable then he may need to do this. It WILL be expensive and you have to work out who needs to pay.

If you picked this installer over others due to price then there is a good chance that the other installers priced to replace the cable.

Of course, this is assuming that the cable IS too small. Where did you get the figure of 1.2 ohms from?

 

[GaryM]

Of course, this is assuming that the cable IS too small. Where did you get the figure of 1.2 ohms from?

Reading between the lines, it looks like it's been given to him by his installer.
Not sure if that's an R1+R2 value or a Zs value, taking into account Ze.

 

[nowty]

Just ran this through an online voltage drop calculator and for a 3% voltage drop based upon 240v @ 16 amps the wire size comes out at around 10mm. But as thats on the limit, a cable size of 16mm would be better.