Ac cable size ???

[matt25]

Hi, could someone please tell me what cable size/type they would use on a 3.6kwp pv system?Many thanks in advance

 

[erf151an001]

Id go for 4mm T&E if its domestic and you can back it up easily with 30 Ma RCD unit. Separate from existing RCD, I prefer. Or Go for 4mm2 SWA then it has the earthed sheath and is protected by nails screws and the like and doesnt need the 30mA RCD protection. Might be seen as over the top but to acheive the 1% volt you wont be far off I think.

 

[Ramjam]

If you are using SMA inverters then the sunny design software will tell you what you need for whatever length of cable run you enter.

 

[matt25]

Thank you

 

[matt25]

Can flex be used instead of t&e?

 

[grandfortune]

you lot not just spurring off the ring main??

 

[Graeme Harrold]

Do your cable calcs properly for a 1%VD, or follow manufacturers instructions. For all we know you have a 50m run.

For example SMA Sunnyboy 4000TL requires a min 6mm T&E

 

[matt25]

The length of run is 5mtrs max, thankyou for the advice

 

[malcolmsanford]

Id go for 4mm T&E if its domestic and you can back it up easily with 30 Ma RCD unit. Separate from existing RCD, I prefer. Or Go for 4mm2 SWA then it has the earthed sheath and is protected by nails screws and the like and doesnt need the 30mA RCD protection. Might be seen as over the top but to acheive the 1% volt you wont be far off I think.

Is there a reason for that?
If using just a sperate RCD how are you providing overload protection?

 

[erf151an001]

Hi yes sorry didnt make myself clear.

I have been told its best to keep the PV circuit on its own dedicated RCD. Apparantly it can cause the RCD to trip on occaision. Nuisance tripping not ideal. You could use a small 3 way unit as used in a garage RCD then through and MCB. Or alternatively a dedicated RCBO on the non RCD side of say for instance a 16th edition board.


Or like I say if you run the cable externally, use SWA instead of T&E in conduit. Just another option. Then you dont need the RCD protection. Just the extra cost work of terminating your SWA glands.

 

[malcolmsanford]

Thanks for the answer, did whoever tell you if there was a technical reason the RCD tripped? The invertor will leak protective conductor currents but are they unusual high on a PV invertor?

 

[Mark Davey]

Do your cable calcs properly for a 1%VD, or follow manufacturers instructions. For all we know you have a 50m run.

please can you comment on where the recommendation for 1% volt drop on the AC circuit to the inverter is?

 

[BruceB]

DTI Guide page 26 is the 1%.
Also, I would recommend only putting it on a rcd if you need to (TT, buried in wall etc). If no need then do not do it as it it only one more thing to cause a problem.
Regards
Bruce

 

[grandfortune]

you need to put it on its own RCD not on a RCD side of a 16th or 17th Edition board, ideally a high integrity board would be best with its own RCBO.

 

[malcolmsanford]

you need to put it on its own RCD not on a RCD side of a 16th or 17th Edition board, ideally a high integrity board would be best with its own RCBO.

Again I ask the same question why??