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Topic Title: MCS assesment PV today
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Created On: 06 September 2013 01:17 AM
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 06 September 2013 01:17 AM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

For any pv guys please.

We install from either Henley blocks or dedicated non rcd to a new sub rcd board and wire from there.


Todays assessor (Niceic) totally confused why we installed hengly blocks and installed rcd 16amp board instead of using a spare 16amp rcd protected mcb, 17th edition board, rcd did all sockets cooker shower etc.

My response: dedicated new sub board installed as to keep maximum trip times satisfactory for rest of rcd protected house wiring as inverters can take up to 5 seconds to shut down blowing my maximum disconnection times out the water for the ring mains circuits for example. His answer was "im not sure on this, I dont really know, fantastic point, and ill need to check with a couple of other assessors and get back to you".

I am doing another pv install tomorrow and I will be letting inverter grid tie and then doing all of my rcd trip times as I feel the email response is debatable. Copy of his emailed few hours later to office:
Hello
 I had a discussion with Douglas on site & I said I would seek clarification & he requested some feedback, this was the feedback I got;  When connecting directly to a 17th Ed split RCD protected board by utilising a RCD protected MCB for the PV circuit as long as the RCD is double pole it should meet current requirements as by taking out the neutral as this breaks the circuit to the grid, single pole RCBOs would not provide the protection required,  although inverters have to be G83 compliant for the shut down in the event of a loss of power most are designed to shut down well within the timescale & most will have a shut down time will be in line with RCD times Although this is different from how Douglas had configured the protection what he had done would be considered best practise  Kind regards

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 06 September 2013 01:26 AM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

Just looked at ofgems final draft dated August 2012 stating all inverters must have a shutdown of not more than 1second.

Just answered possibly my own question. Stumbled over a fronius data sheet showing inverter shut down times max time as 437ms.

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 06 September 2013 01:26 AM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

Just looked at ofgems final draft dated August 2012 stating all inverters must have a shutdown of not more than 1second.

Just answered possibly my own question. Stumbled over a fronius data sheet showing inverter shut down times max time as 437ms.

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 06 September 2013 06:14 PM
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Grumpy

Posts: 428
Joined: 09 January 2009

Hey Dougie, are you doing much PV instal? There was so little happening round here that I let my MCS lapse. Went from flat out to flat line lol!!
 06 September 2013 09:15 PM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

Yes were doing installs, most companies have dropped there roofers and sparks and using companies like me and subby the full install out to us when they sell a job as they dont have the workload for full time employees.

Most MCS companies around i find are a sales team and office admin now with only subbies as installers.

Works for us and for them. At present were installing 2-5 a week domestic

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 07 September 2013 01:14 PM
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alancapon

Posts: 5766
Joined: 27 December 2005

I believe that G.83 still allows 5 seconds for an inverter to disconnect following loss of mains, providing that the inverter is capable of accepting the incoming supply back 180° out of phase without damage. If the inverter cannot accept this phase shift, then a much lower limit (which I cannot remember) applies.

Regards,

Alan.
 07 September 2013 01:59 PM
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weirdbeard

Posts: 1523
Joined: 26 September 2011

Originally posted by: DOUGIE1000

I feel the email response is debatable. Copy of his emailed few hours later to office:

Hello

 I had a discussion with Douglas on site & I said I would seek clarification & he requested some feedback, this was the feedback I got;  When connecting directly to a 17th Ed split RCD protected board by utilising a RCD protected MCB for the PV circuit as long as the RCD is double pole it should meet current requirements as by taking out the neutral as this breaks the circuit to the grid, single pole RCBOs would not provide the protection required,  although inverters have to be G83 compliant for the shut down in the event of a loss of power most are designed to shut down well within the timescale & most will have a shut down time will be in line with RCD times Although this is different from how Douglas had configured the protection what he had done would be considered best practise  Kind regards


Hi dougie, what's debatable about their reply, it seems to be in your favour!???

It seems to me that you have provided a service to the NICEIC as before the visit to you it seems the assessor was unaware of what is considered best practice - in lieu you should ask head office for a discount on next years fees, or something.
 07 September 2013 02:41 PM
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daveparry1

Posts: 6201
Joined: 04 July 2007

Judging by what Grumpy and Dougie have said it sounds like the public are starting to realise what a waste of time financially PV is in the domestic environment!

Dave.
 07 September 2013 02:51 PM
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Grumpy

Posts: 428
Joined: 09 January 2009

Originally posted by: daveparry1

Judging by what Grumpy and Dougie have said it sounds like the public are starting to realise what a waste of time financially PV is in the domestic environment!



Dave.


As I did my own house it cost about £6k and you generous electricity consumers pay me about £1100 a year, index linked, tax free for the next twenty three years and six months for which I thank you.
However, Dave, I agree totally with you. Whereas it might not be a waste of time financially on a personal level on a national level all these over subsidised bloated "green" initiatives are a scandal.
 07 September 2013 03:56 PM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

Not sure if my point has come across clearly, a fault on a rcd set of circuits and the inverter will keep pumping 240volt power into the tripped rcd for up to 5seconds after the rcd has tripped.

Yes assessor has carried I have identified we do best practice. Unfortunatly I didnt have time to test fridays install and will do rcd times next install I do.

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 09 September 2013 10:35 AM
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AJJewsbury

Posts: 11448
Joined: 13 August 2003

Not sure if my point has come across clearly, a fault on a rcd set of circuits and the inverter will keep pumping 240volt power into the tripped rcd for up to 5seconds after the rcd has tripped.

Reg 551.7.2 - the wording isn't that clear, but as I read it:

If the PV is connected to the rest of the system upstream of other circuit's protective devices (both overcurrent and residual) - then all's well as other circuits' protection operates as normal. (Dougie's method).

If the PV is connected downstream of a protective device that also serves other circuits then (as Dougie says) disconnection times of those other circuits might be compromised. This is allowed however if (amongst other constraints, including lots of current carrying ones) if the upstream protective device disconnects N as well as L. Thus one of the other circuits protection is called upon, the inverter might be kicking out 230V still, but it's de-referenced from earth - making it effectively a separated system, so removing the risk of electric shock to earth (which is what the RCD was trying to achieve anyway) even without disconnection.

You might think that such approach in a domestic is against the spirit of putting 418.3 (Electrical separation for more than one item) under 418 (Protective measures only installations under the control of skilled/instructed persons), but I don't suppose it'll be any less effective for that.
- Andy.
 09 September 2013 10:46 PM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

Ill throw some rcd tests at our next install and update this thread

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 10 September 2013 09:48 AM
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AJJewsbury

Posts: 11448
Joined: 13 August 2003

Reg 551.7.2

Looking further, 712.411.3.2.1.1 (specifically for PV systems) takes a slightly different approach - demanding that the PV connection is made upstream of ADS protective devices for other circuits under all circumstances. I guess the question then is whether the RCCB is there for ADS or just additional protection. If the RCCB is just for additional protection, then the connection is to be busbar upstream of the MCB and so ADS operates normally. If the RCCB is needed for ADS (e.g. TT system or TN with high Zs on some circuits) then the connection would need to be upstream of the RCCB. So Dougie might be right after all.

- Andy.
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