Adding PV array into existing circuit?

[DomB]

Hi all,

Do you have any thoughts on hooking a PV array's inverter onto an existing circuit, say a ring final? Obvioulsy as long as the cable was good (2.5mm for instance) I wonder what issues there are with doing that..

Cheers for any replies!

 

[Markc]

That's a no no! PV must be on a dedicated circuit and not in with an existing. If no spare way fit a stand alone board. It's not going to cost that much.

 

[SolarCity]

Are you sure about that, Mark? It was my understanding that doubling up onto an existing breaker was permissable.

To be honest, even though I believe it is accepted, I would say it is bad practice and like Mark says I would strongly recommend fitting a seperate CU for the new circuit.

 

[DomB]

So I've looked at the MCS doc on Solar PV and it says "all double-ticked items in the DTI guide are mandatory".

The DTI guide (http://www.bre.co.uk/filelibrary/pdf/rpts/Guide_to_the_installation_of_PV_systems_2nd_Edition.pdf) then says (and this part is double ticked):

"An inverter supplied from a PV array must preferably be installed in a dedicated circuit in which:
no current-using equipment is connected, and
no provision is made for the connection of current-using equipment,
and
no socket-outlets are permitted"

So I guess it's a dedicated circuit.

Mine is not to question why...

Cheers

 

[JulianC]

"An inverter supplied from a PV array must preferably be installed in a dedicated circuit ..."

Hmm, as ambiguous as ever with the use of the word preferably. There is a guide from ESC that says it's OK to connect into an existing circuit providing the wiring can handle the combined current of that from the PV system and that capable of being pulled through the breaker. I would imagine this would be difficult to confirm in many real world scenarios.

I agree that it doesn't seem like good practice and I wouldn't entertain the idea. A new circuit on a new breaker everytime, on a new CU if necessary.

 

[Markc]

I love that Preferably. I can't see how anyone could be criticised for keeping it on a dedicated but might be over doubling up. May be putting MUST in my post was a mistake. Sorry.

 

[edexlab]

I read that ESC guide and looked into this , ( i tend to fit a new Cu just for pv as standard ) but my thinking was more geared to using existing submains ie outbuildings etc
and this term of existing final circuit allows this, subject to cable size/load .

 

[bigbob1]

G83/1

Small Scale Embedded Generator (SSEG)​

A source of electrical energy and all associated interface equipment, rated up to and including
16 A per phase, single or multi phase 230/400 V ac and designed to operate in parallel with a​

public low voltage distribution Network.

5.2 Installation Wiring and Isolation​

The installation that connects the SSEG to the Supply Terminals shall comply with the
requirements of BS 7671. All wiring between the Supply Terminals and the SSEG shall be
protected by a suitably rated protective device; and shall be of suitable size and type for the​

rating of the SSEG.

I say go and do it, then on your test sheet write down 32A mcb and see what happens! and then go get a socket rated at 16Amps blah blah blah

 

[edexlab]

perhaps i did'nt explain my last post very well ,what i should have said was a dedicated pv circuit, connected into a consumer unit off a suitably rated submain .
I've had a good chat with Niceic and two separate DNO's talked about 1% vd limit and they were happy with this although they agreed this may be difficult to achieve.
As for connecting into an existing circuit i agree not a good idea!

 

[bigbob1]

if you just follow dti guide, mis 3002 and G83/1 you can't go wrong.

 

[Energetic]

Have come across this recently, what i thought would be an dedicated submain to a garage seems to be coming off an unknown circuit. Only at the initial enquiry point so have not installed anything, the CU is right up the other end of the immaculate cottage, no chance of running another circuit in... Would only be a small system and not worth the hassle...

Any way to get round it?

 

[Worcester]

View attachment Best Practice Guide 5.pdf Well the NIC EIC reckon it's OK (pages 11-13)

 

[bigbob1]

anyone can install a pv system on a property, as long as it is part P'd. If your not MCS accredited the customer will not get the feed in tariff. You must install the system in accordance with the dti guide to installing photovoltaic systems 2nd edition, and IEE Guidance Note 7 to BS 7671 - Special Locations, Section 12 SolarPhotovoltaic (PV) Power Supply Systems (ISBN 0 85296 995 3, 2003). Also attention must be paid to section 2.3.1 which states An inverter supplied from a PV array must preferably be installed in a
dedicated circuit in which:no current-using equipment is connected, and
no provision is made for the connection of current-using equipment,
and no socket-outlets are permitted.
An inverter must not be connected by means of a plug with contacts
which may be live when exposed.
Where an electrical installation includes a PV power supply system
without at least simple separation between the a.c. side and the d.c.
side, an RCD installed to provide fault protection by automatic
disconnection of supply must be type B RCD according to BS EN 60898
(IEC 60755, amendment 2).
a.c. cables are to be specified and installed in accordance with BS 7671.

A manual a.c. switch-disconnector must be provided located in an
accessible position within the Customer’s installation as in G83/1 (e.g.
adjacent to the consumer unit or main distribution board), which is
in accordance with BS 60947-3

must switch all live and neutral conductors.

must be securable in the OFF position only. It must be simple to secure

using a standard padlock
So unless you follow those rules, which plainly states no to "hooking up to anexisting circuit" and follow the rules set out for industry, if i was you i wouldn't do it!

 

[bigbob1]

As an electrician there is no hassle in doing it correctly and running a 4mm cable in from the inverter to the fuseboard and putting it on a 16A mcb (rcd protected). Then you can use that job to get your MCS as long as you've followed the rules.

 

[bigbob1]

Also the system must be registered within 30 days to the local Distribution Network Operator and fully comply with engineering recommendation G83/1....... Get reading!

 

[johnboy6083]

As far as im concerned, i think it is very dangerous to have an alternative supply tapped into a final circuit. im not PV trained so i dont understand the finer points of PV installation, but i think that in general its not to be done. labells fall off, boards get damaged, and tenants change. also even competant experianced sparks are guilty of not testing dead all of the time.

 

[BruceB]

In principle, it is possible to have microgeneration connected into existing circuits. BS7671 does allow it and it features in the BPG that Worcester cited because that is expressing the 'general' case. However for Solar PV we MCS types are required to follow the DTI guide which says 'must preferably' be a separate circuit. Not 100%, but not far short! If you do install into an existing final circuit then make sure you read and understand 551.7 which is not trivial.

Regards
Bruce

 

[Worcester]

@BruceB Spot on!

Sometimes I think people jump in here before reading the guidelines they are supposed to know to become MCS.

I was at a renewables conference this week that lamented how many small firms were now MCS registered that really didn't know what they were doing and so thereby had devalued the MCS qualification, and as such MCS could no longer be used as a gaurantee of getting good, quality advice that could be assumed to be correct. And they should look for a track record of similar projects to judge their capability.

This was I must admit aimed a a group of people that would in the past have beed considering roo-fit installations and were now being 'pestered' by loads of MCS qualaified organisations without experience of larger scale projects.

Interesting, that people are saying this..

 

[bigbob1]

. http://www.dailymail.co.uk/news/article-2007510/Great-solar-power-Rogue-salesmen-overestimate-savings-green-panels-provide-households.html Read on, i personally believe that PV is a game for sparks, but there is selling involved and money to be made, i am affraid that of the 2400 odd mcs companies out there you can guarantee 2000 of them are window and door companies with a knock you on the head sales approach, with guys that do not really understand the full in's and out's of this industry. But saying that they're not going to be able to help build 8 new power stations, and that in itself destroys the longevity of the solar industry. Germany 100% renewables within 20, UK 30% within 9 then nuclear you can look at it like this really america 5 litre engines uk about 2 litre we're tiny country so why bother trying to cut down on co2? which is a myth in itself, because wether tv's on stand by or not or lights left on or not the turbines are still spinning at the power plant, which is creating the co2!

 

[BruceB]

Worcester, I spent 36 years in the Services and for the latter 10 years saw so often examples where process came to dominate over substance of what we were trying to achieve. The same is happening with MCS. I have been assessed for GSHP, ASHP and PV and I did expect some discussion of the engineering judgements I had made on my initial installations, because they were real, tricky installations, not just a simple 2kW on my own roof. There was no engineering discussion. The focus was almost entirely on the paperwork - that the bases had been covered in the QMS and in the information provided to the customer. I do not have a simple solution to offer though because I bridle at over regulation of activities.
Regards
Bruce