Cu & Pv Configuration

[binky]

Firk knows :^O

 

[the doctor]

Doc, dont get me wrong,

theory isnt my big point, but I do know what I see in the real world,

sometimes I need folks on here, [like yourself, SW, boaty, FSOTM, etc ] to explain it to me,

I can just say what I know happens,

I still dont see how an RCD tripping equates to IT ,

the earth is still present, IT is without earth surely?

thats how rigs/battleships work, they simply have a warning illuminate, there is NO earth whatsoever, almost like a car sort of thing, N is Earth

BTW, isnt IT NOT allowed under normal conditions...?

Hi Steptoe,  Try this...IT.pdf

The victim is smiling and safe.  The arrows it the circuit that would kill him if the neutral was closed.  

An IT system basically means the supply floats above earth, a bit like a shaver socket i guess.

 

[Sidewinder]

No Doc, your sketch does not include sufficient detail as to how the DC/AC solar inverter handles the conversion.

As I have said previously this is a system level view.

It is a component level scenario that will kill.

Unless you can fully specify the performance of ALL solar inverters on a component level, with and without synchronisation supply, then this sort of sketch is irrelevant.

None of the inverter manufacturers AFAIK will let this sort of information into the public domain, so until they ALL do, we HAVE to take it that the inverter is NOT islanded.

If you want to assume it is, then fine but, you know what assume is don't you?

It makes an *** out or U and me?...

I don't do guessing or assumptions unless they are in a model where there is inadequate information, then I detail them in the foreword to the calculations and the proposal.

Which TBH, this is one of them and, I would rather assume that they are dangerous, and save lives, than assume they are safe and perhaps kill someone, or set fire to a property.

 

[the doctor]

Hi Sidewinder,

I have not shown the earth on the inverter for clarity.  However the thing is built, the frame is an exposed conductive part with the magic bit tucked inside.  The drawing is a general  show of the point made way back by Phoenix.  As long as there is no insulation fault anywhere and it is is as drawn it is impossible to be shocked from a pumping PV and a tripped RCD.  It is effectively an IT system.  I am not saying this is good or cool, but stating the way it appears to be.  In the regs, they talk about 'single fault conditions'.  This situation is exactly that. If you somehow made contact with the neutral side that would be classed as a second fault.  You cannot protect against a second fault because it would be the equivalent of sticking two fingers in a lamp holder.

 

[Sidewinder]

Doc,

I am NOT trying to bring in a 2nd fault.

You are looking at a system view as I have already stated, a system view is inadequate, you MUST look at a component level view to see how the system behaves on a component level.

I still say that this scenario is unsafe, and until you can provide data from every inverter manufacturer stating that when the mains drops out the inverter immediately goes islanded and is totally disconnected from the mains supply, such that it cannot pose a dangerous situation, then there is no way that you can change my mind.

Remember that it is the exception that proves the rule, if you can prove the rule, and get a statement from, all and every solar inverter manufacturer that the scenario is as you describe, then the potential lethal fault scenario exists.

So, sorry Doc, court, ball yours, as it could be said.

 

[the doctor]

Most (if not all) PV inverters will have some sort of EMC filter on the AC side - That will be an RC maybe inductor network connected to earth

Excellent point canoeboy.....

 

[binky]

can't be totally isolated from mains - how else can it monitor, but must be designed not to output any power whilst in that state

 

[the doctor]

As I said before, this whole business sort of snook up on me.  I had read the regulation about not connecting on the downstream side of a protective device that supplies other circuits.  However, I did not click on the significance of it.  The strangest thing is that despite its importance, it has not been discussed previously and more importantly is not mentioned in any books I have come across including the MCS bible on PV systems  :Blushing

 

[binky]

give it a few years and MCS may catch-up eventually :slap

 

[the doctor]

give it a few years and MCS may catch-up eventually :slap

Hi Binky... perhaps but here is another thought that occurred to me today.There should be a regulation that states along the lines of...

A PV generator shall not be installed on any installation, which by its nature is protected by an RCD.

In other words... following on from this thread, a PV cannot be fitted on any TT job unless it gets its own unit and RCD

 

[Sharpend]

Nice one doc! That'll be the fourth amendment!

 

[steptoe]

Hi Binky... perhaps but here is another thought that occurred to me today.There should be a regulation that states along the lines of...

A PV generator shall not be installed on any installation, which by its nature is protected by an RCD.

In other words... following on from this thread, a PV cannot be fitted on any TT job unless it gets its own unit and RCD

there is already one to that effect doc,

manufacturers instructions ,

plus the MCS requirements ,

 

[Andy™]

Hi Binky... perhaps but here is another thought that occurred to me today.There should be a regulation that states along the lines of...

A PV generator shall not be installed on any installation, which by its nature is protected by an RCD.

In other words... following on from this thread, a PV cannot be fitted on any TT job unless it gets its own unit and RCD

there pretty much is. states inverter must not share the same RCD as another circuit

 

[the doctor]

there pretty much is. states inverter must not share the same RCD as another circuit

Yes, but it would be handy if there was  note or something, explaining the point.... and the reg mentions 'protective device'  a little cryptic for me.

 

[Adrian]

there pretty much is. states inverter must not share the same RCD as another circuit

What is the reg that states that 

 

[Andy™]

What is the reg that states that 

maybe try reading the reply in your other thread asking the same thing?

 

[Adrian]

Sorry Andy did not see that you had replied to this as I was busy reading the other thread  thanks for the reply