what can I do

[Matt_M]

To achieve a 1% volt drop at 140m you would need 35mm2 cable and that would only just meet 1% - that's a big cable

 

[SolarCity]

It is a big cable, but it's what I'd use. Do it right, do it once.

 

[powervan]

MEGGA BUCKS!!! installer should of known!! but try be fair with him half and half?

 

[Noshocks]

Suggest you dont give too much away regarding location or you may get a visit from our big fat gypsy friends, the cost of that cable will make your eyes water.

 

[potatoman]

The way the installer worked it out was he took a reading at the meter which was .4 then took a reading at the end of the cable which was 1.2 took one from the other and told me the restsrance is .8 and the PV would work ok .When I rung SMA they tell me the resistance is 1.2 and the inverter will trip out

 

[moggy1968]

It looks like he's taken what is called a Ze reading at the meter and a Zs at the end of the cable. These are basically the resistance readings at those points of the circuit. By taking one from the other you can calculate the resistance of the cable run taking account of things like connections and bends in the cable which may increase resistance.
I think SMA have missunderstood what the 1.2 is, that that is a Zs reading, not the resistance of the cable.

 

[Glen Powell]

In some inverters you are able to increase the voltage to compensate the resistance, this is really not the answer as the correct cable size should have been calculated in the first place. I do not know if you can re calibrate the SMA as I do not deal with them.

 

[SolarCity]

In some inverters you are able to increase the voltage to compensate the resistance.

I wasn't aware of that? Would this not affect the G83 certification?

 

[potatoman]

Thanks for your reply I will contact SMA on Monday about the Ze and Zs values,am I right in saying if the resistance is correct ,less than 1 ohm, and the volt drop is less than 3% the cable will be ok

 

[cook1e]

the person responsible for the design, constuction and testing should be responsible for putting it right, a zs reading - a ze reading is not a true cable resistance reading and never will be,

threaten to report them to their professional body and sue them if they dont fix the problem

Martin

 

[SolarCity]

It is my understanding that volt drop should be less than 1%

 

[potatoman]

Is ther anything more I should consider with the cable

 

[GaryM]

From Photovoltaics in Buildings Guide to the installation of PV systems 2nd Edition

The a.c. cable connecting the inverter(s) to the consumer unit should be oversized to minimise voltage drop. A 1% drop or less is recommended. However in larger installations this may not be practicable or economic due to the very large size of cable resulting. In this case the designer should minimise voltage drop as far as possible and must remain within voltage drop limits as prescribed by BS 7671.

Note: When generating, the voltage at the inverter terminals is higher than the voltage at the consumer unit. This voltage drop must be kept to a minimum in order to prevent the inverter nuisance tripping on over voltage.

 

[potatoman]

Any idear what the voltage drop limits as prescribed by BS 7671 are

 

[GaryM]

Any idear what the voltage drop limits as prescribed by BS 7671 are

5%

Over 100M it may be increased by 0.005% per meter of the wiring system beyond 100%, without this increase being greater than 0.5%.