Disconnection time for existing circuits.

[Hefferl]

Hi.

looking for the thread that discusses the impact upon the disconnection times of existing circuits when a PV install is done via a spare way in an existing CU but can't find it (it was a while ago) - can anyone point me in the right direction please?

I was reminded of this thread when reading today's earlier thread about someone's new job testing PV installs and wanted to revisit it (Strangely i cant find that thread from earlier today either?)

Cheers

 

[Doc Hudson]

A member called 'Blank' did start a thread on this topic in the solar PV forum, but he has subsequently deleted it. His profile now confirms no posts made or threads started. View Profile: Blank - Talk.electricianforum.co.uk... a forum with a difference. This is probably why you cannot find it. Admin & Mods can see reference to three post that were there 17:10, 17:28, 17:41 but now deleted. The thread had 7 replies to it, I guess this is what you read? Just for the record I will add that members can delete their own posts and threads. It is not the moderators stifling anyones freedom of speech.

Doc H.

 

[Hefferl]

Thanks Doc - I wasnt suggesting anything clandestine just trying to give enough info so that someone could help me find the original thread which I was reminded of by something that was posted in today's thread

A member called 'Blank' did start a thread on this topic in the solar PV forum, but he has subsequently deleted it. His profile now confirms no posts made or threads started. View Profile: Blank - Talk.electricianforum.co.uk... a forum with a difference. This is probably why you cannot find it. Admin & Mods can see reference to three post that were there 17:10, 17:28, 17:41 but now deleted. The thread had 7 replies to it, I guess this is what you read? Just for the record I will add that members can delete their own posts and threads. It is not the moderators stifling anyones freedom of speech.Doc H.

 

[Andy™]

i can remember that thread, but i couldnt find it either. and im pretty sure there were more than 7 replies

 

[Hardy Sparky (Mvc)]

What a surprise the gov let us all do courses and then!!!! Well you can guess !!!!!

 

[binky]

Seem to remeber KME replying to thread. It went along the lines of not feeding PV onto RCD side of CU cos disconection time of inverter (approx 5secs or more depending on make) is longer than that allowed for circuit ergo RCD trips around 40ms, but PV continues to feed leccy into system - potentially nasty!!

I have since mostly fitted mini CUs to meter tail blocks since.

 

[Hefferl]

Yeah thanks thats the one - now I just need to find the thread itself....

Seem to remeber KME replying to thread. It went along the lines of not feeding PV onto RCD side of CU cos disconection time of inverter (approx 5secs or more depending on make) is longer than that allowed for circuit ergo RCD trips around 40ms, but PV continues to feed leccy into system - potentially nasty!!I have since mostly fitted mini CUs to meter tail blocks since.

 

[steptoe]

what is it you need to know?

basically a normal inverter must shut down within 5s of the supply being disconnected,

obviously this means a PV inverter 'can' still be backfeeding the supply for over 4s after the supply has been shut off,

now, if you were to feed this inverter from the RCD side of a board, if a fault were to happen to trip the RCD what do you think might happen as regards the PV inverter backfeed?

is this what you are getting st?

 

[Hefferl]

Thanks Steps. I wanted to read the thread to get people's various views surrounding this issue but your synopsis is much appreciated.

In answer to your question I presume the inverter would then be supplying all the other circuits on that busbar (including the faulty one) until it's shutdown was complete.

what is it you need to know?basically a normal inverter must shut down within 5s of the supply being disconnected,

obviously this means a PV inverter 'can' still be backfeeding the supply for over 4s after the supply has been shut off,

now, if you were to feed this inverter from the RCD side of a board, if a fault were to happen to trip the RCD what do you think might happen as regards the PV inverter backfeed?

is this what you are getting st?

 

[steptoe]

YES,

that is basically the problem with feeding the inverter from the load side of the RCD,

the RCD shuts down much faster than the PV, over 4&1/2 secs faster.

I have always fitted stand-alone boards for my PV where RCDs have been present.

 

[kme]

I thought that thread was in here somewhere....I KNOW it was here somewhere, `cos I recall posting it!

 

[a1]

I have now undeleted the thread and closed it - so it is just there for reference. (I haven't read the thread yet, but will do, later, hopefully).

http://www.talk.electricianforum.co.uk/photovoltaic-panels-pv-solar-panels-green-energy-forum-wind-turbines-renewable-energy/18841-please-help-starting-new-job-tomorrow-testing-pv.html

 

[kme]

Nah mate - I meant my original post about it.....

Will go and have a look.....

 

[Hefferl]

Sorry if I have caused any confusion - it was in fact kme's original that I was trying to locate.