Cu & Pv Configuration

[the doctor]

However you look at it - Its still dangerous - Solar should be fed into the mains incomer on its own dedicated circuit and not interfere with any other circuits

Most RCDs / RCBOs wont work on a Solar PV inverter - so again this is another dangerous scenario

Most installs i have seen are done by the cowboys with spurs - its to put pun to it SHOCKING

MCS is and was supposed to raise standards - However it didn't / hasn't and is still being flaunted 

I agree fully canoeboy, but Phoenix's point was valid and perhaps it has nudged us to where we are now with the reg being 'ignored' and not even mentioned in the ECA benchmark industry guide...

 

[Sidewinder]

Ker pow Phoenix is correct.  If you drive this imaginary nail into a wire and the RCD trips, the inverter then becomes electrically separate so you cannot get a shock to earth.  I wonder is why this regulation 712.411.3.2.1.1 is effectively ignored by the industry perhaps,,, :innocent

The house, in Ireland,  is a bastardised TNCS which they call a ' neutralized supply'  with an installation earth rod fitted.  Don't fancy a mini cu and I cannot afford RCBOs :facepalm:

That relies on the inverter being electrically separate, is it?

Are you sure, can you guarantee it?

 

[the doctor]

thats a big if

I see loads of these in council properties where the RCD simply doesnt trip while the PV is energised.

Hi Steptoe,

Every install we work on gets the full test. The only issue we have come across is RCDs tripping out.  Perhaps we have been fortunate till now.  As conoeboy says it is shocking...

 

[binky]

all inverters I've fitted have an earth connection - extraneous conductive part etc etc

RCBOs can be ha vry cheaply like £13 each, less from forum sponsor SBS Dave. As you have a suppliers earth I don't see a requirement for RCD for Inverter, but I'm not familiar with NI electrics

 

[steptoe]

all inverters I've fitted have an earth connection - extraneous conductive part etc etc

RCBOs can be ha vry cheaply like £13 each, less from forum sponsor SBS Dave. As you have a suppliers earth I don't see a requirement for RCD for Inverter, but I'm not familiar with NI electrics

NI is the same as GB except lots of TT, its very common,

EIRE is different in the combine NE and use a rod as primary E, almost a proper PME imo tbh, but they will NOT allow you to rely on their Earth.

 

[the doctor]

That relies on the inverter being electrically separate, is it?

Are you sure, can you guarantee it?

 No Sidewinder,  You are missing the point that Phoenix makes

I drew it out to get it in my mind. When (if) the RCD main switch trips on an earth fault the both the L and N are disconnected from the supply.  Even if the inverter carries on pumping, you cannot get a shock as the whole installation ( the pv AND the rest) becomes separated from earth. You could only get a shock by touching L and N at the same time and you have no protection from that in any installation.  It is a valid point and effectively negates 712.411.3.2.1.1

I am not suggesting anyone flaunts the rules, but it appears with its lack of publicity, to be  regulation  that is 'ignored'

 

[steptoe]

but, on a TNCS they are not disconnected,

the N is still connected via the Earth.

 

[binky]

and inverter is still back feeding leccy into circuits shared with same RCD

 

[ProDave]

 No Sidewinder,  You are missing the point that Phoenix makes

I drew it out to get it in my mind. When (if) the RCD main switch trips on an earth fault the both the L and N are disconnected from the supply.  Even if the inverter carries on pumping, you cannot get a shock as the whole installation ( the pv AND the rest) becomes separated from earth. You could only get a shock by touching L and N at the same time and you have no protection from that in any installation.  It is a valid point and effectively negates 712.411.3.2.1.1

I am not suggesting anyone flaunts the rules, but it appears with its lack of publicity, to be  regulation  that is 'ignored'

You are assuming the victim is receiving a L-E shock.

What if he's got L in one hand and N in the other. the imbalance to earth resulting will hopefully trip the rcd, but he would still continue receiving the shock until the inverter shuts down.

Want to take a chance that it's always a L-E shock?

 

[the doctor]

but, on a TNCS they are not disconnected,

the N is still connected via the Earth.

Hi Steptoe,

It makes no difference.  As Phoenix alludes, when the RCD opens the neutral is disconnected. The fact that it connected to the earth at the cut out is irrelevant.  The inverter can pump away and any contact is 'electrically separate' a la a shaver socket.

 

[steptoe]

Hi Steptoe,

It makes no difference.  As Phoenix alludes, when the RCD opens the neutral is disconnected. The fact that it connected to the earth at the cut out is irrelevant.  The inverter can pump away and any contact is 'electrically separate' a la a shaver socket.

doc,

that is totally different,

a shaver socket is isolated, [normally]

think about it,

and you are a much better educated man than I

 

[the doctor]

You are assuming the victim is receiving a L-E shock.

What if he's got L in one hand and N in the other. the imbalance to earth resulting will hopefully trip the rcd, but he would still continue receiving the shock until the inverter shuts down.

Want to take a chance that it's always a L-E shock?

Hi Prodave,

The assumption of L-E was based on your original comment with the man driving the nail in the wall and getting a shock which trips the RCD, however. he then is to be electrocuted by the G83 inverter.  Pheonix has stated, correctly that this is not so.  As to the L to N shock scenario, this is the basis of a BS7671 ' second fault situation'

This point is also moot.  BS 7671 cannot protect against a 'double fault situation'  If you stick one finger in the line and one in the neutral it will end in tears and nothing will protect you.

doc,

that is totally different,

a shaver socket is isolated, [normally]

think about it,

and you are a much better educated man than I

Hi Steptoe,

Draw it out for yourself.... I did not see it either.  The inverter is pumping away connected to all the circuits because the main RCD has tripped.  The system is now essentially an IT install with no earth path

 

[steptoe]

Hi Prodave,

The assumption of L-E was based on your original comment with the man driving the nail in the wall and getting a shock which trips the RCD, however. he then is to be electrocuted by the G83 inverter.  Pheonix has stated, correctly that this is not so.  As to the L to N shock scenario, this is the basis of a BS7671 ' second fault situation'

This point is also moot.  BS 7671 cannot protect against a 'double fault situation'  If you stick one finger in the line and one in the neutral it will end in tears and nothing will protect you.

Hi Steptoe,

Draw it out for yourself.... I did not see it either.  The inverter is pumping away connected to all the circuits because the main RCD has tripped.  The system is now essentially an IT install with no earth path

this is my point Doc,

I have seen well in excess of probably 500 installs in the past 3 or 4 years where the RCD will NOT trip while the PV is backfeeding it,

I do many hundreds of council houses per year, and there are >90% bad installs

 

[the doctor]

Anyway.... on a job today I looked really clever informing the contractor that the install was dangerous because of the problem spoke of here.  Worse still it was a three phase RCD with a  (solid neutral)  so it the event of a trip the inverters would not be isolated from earth.... OUCH

Hi Steptoe....

Yes it is bad and I am embarrassed/humbled that I never saw it before now.  But that is the beauty of this fine forum, where members can bounce stuff around to get the extra knowledge.  

As I always say to students when doing some occasional college work 'When people really discover how to use google, people like me will be finished off, like the dinosaurs we are..   :coat  .'

 

[steptoe]

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...?

 

[binky]

Doc, link to earth doesn't rely on Neutral conductor within CU, earth-neutral link is after any RCD ie at the consumer head, so tripped RCD does not remove earth path on any standard system. And we are of course forgetting bonding and parallel earth paths. Lots of opportunities for L-E shock N-E shock from working inverter.

 

[NozSpark]

You cannot get a L-E or N-E shock from a PV inverter if the L&N are isolated from the supply......

Think about the fault path,,, the only reason you can get a L-E shock is because you complete the circuit between the L and the DNO star point

 

[SPECIAL LOCATION]

Now I don't do any solar PV stuff...

But still reading this with interest, from what Noz says am I right in thinking that...

The neutral output of an inverter is NOT tied to Earth in the same way that the Neutral (star point) of the grid generator is tied to earth.?

So if the L & N incoming supply from the grid is open circuit (main switch or D/P RCD open 'off'). 

and we had a hypothetical PV inverter that hadn't switched off due to loss of grid power..

Then there is no connection at all that would allow current to flow from the live of the inverter back to the neutral of the inverter via an earth path?.. 

Or is there?

i.e.  bit like the old C&G question draw the earth loop fault path such as the picture on the TLC info page...http://www.tlc-direct.co.uk/Book/5.3.1.htm

What is the earth loop fault path from an inverters Live conductor via an earthy part????

Which I guess is what the Doc was saying about Shaver socket similarity ???

But if an RCD hasn't operated due to the issues Steps & co refer to..

Then there the Live from Inverter via an earthy part..

via Grid star point or N-E link at main cut out.. 

Then back up N through RCD that hasn't tripped in time..

Back to inverter..!!!

Or have I missed something??

opcorn

 

[binky]

You cannot get a L-E or N-E shock from a PV inverter if the L&N are isolated from the supply......

Think about the fault path,,, the only reason you can get a L-E shock is because you complete the circuit between the L and the DNO star point

we are talking about inverter feeding into CU with circuits shared across a single RCD - think  busbar linking all those nice MCBs, neutral bar at top.... Inverter output maybe stalled, but they contain very large capacitors and coils, ergo there is stored energy that can be present for upto 5 seconds, so if you cut a cable on same RCD there is every chance of getting belted from the inverter until internal relay cuts off output from inverter.

 

[NozSpark]

Binky,,, I never said that you can't get a L-N shock,, but you'll never get a L-E shock after an RCD has tripped