Tail sizes from PV sub-board

[davesparks]

As I said I am not an electrician so bear with me. I am assuming you mean that if using the 10mm tails for the PV connection they should be fused down at the point of connection rather than using an HB.

That’s not what I mean. Overload protection can be installed after the reduction in conductor size in these situations if certain criteria are met.
If feeding a switchfuse or other 1way CU then it can be made to comply easily. If you are leaving spare ways which could be used to feed something else and increase the load then it may be less easy to comply.

 

[davesparks]

Ha - tell your contract engineer to apply Ohm's Law to Ze = 0.35 and Uo.Cmin = 218.5V. Then look up the 100A fuse disconnection time and plug that into the adiabatic equation with k = 115.
Spoiler Alert - 10mm tails seem too small (in this situation) to melt the fuse without themselves being heat affected.

See regulations 433.2.2 and 434.2.1, if installed correctly there can be 3metres of reduced size tails between the meter and the CU without upstream fault protection.

 

[davesparks]

Overload protection would not be the issue however if the 10mm tails are adequately sized for fault protection then it’s acceptable as you stated

Or if you apply 434.2.1

 

[CBR600]

Ok thanks, that makes a bit of sense. The pv board houses an rcbo for the pv and will have a din mounted generation meter. It will have no spare ways.

 

[CBR600]

If there are spare ways why are you not connecting direct to the dist board.

To prevent the chances nuisance tripping the main board.

 

[Leesparkykent]

If there are spare ways why are you not connecting direct to the dist board.

I’ve seen many installed this way that do not comply.

 

[Ian1981]

Or if you apply 434.2.1

Installed in galv trunking perhaps as one method?

 

[davesparks]

Installed in galv trunking perhaps as one method?

Yes, or plastic trunking, properly clipped/restrained depending on the exact location and environment.

 

[davesparks]

To prevent the chances nuisance tripping the main board.

Tripping what and how?

Ok thanks, that makes a bit of sense. The pv board houses an rcbo for the pv and will have a din mounted generation meter. It will have no spare ways.

Is there a main switch in the board?

 

[westward10]

You must have some design criteria for this want of a better words, lash up.

 

[westward10]

To prevent the chances nuisance tripping the main board.

If you are worried your new install is likely to cause nuisance tripping then you need to reassess what you are doing as the best method is to install directly to the existing dist board providing there are spare ways.

 

[Leesparkykent]

If you are worried your new install is likely to cause nuisance tripping then you need to reassess what you are doing as the best method is to install directly to the existing dist board providing there are spare ways.

I wouldnt say it’s the best way if there is spare way on a RCD protected way that shares the same side as a socket circuit for example. It would actually be non compliant due to how long the inverter takes to shut down which can be up to 5 seconds under G83.

 

[Octopus]

If you are worried your new install is likely to cause nuisance tripping then you need to reassess what you are doing as the best method is to install directly to the existing dist board providing there are spare ways.

That's VERY wrong for the reason Lee gave above ........... but is the most common method of install I see ......

 

[CBR600]

Just a quick thanks to everyone for the contributions on this last night. All very helpful.

 

[westward10]

I wouldnt say it’s the best way if there is spare way on a RCD protected way that shares the same side as a socket circuit for example. It would actually be non compliant due to how long the inverter takes to shut down which can be up to 5 seconds under G83.

Where does it state this would be non compliant, not had much to do with these systems so would be interested.