Connecting energy monitors with Solar PV

[SolarCity]

Again it's a matter of personal preference but I think it's less than ideal to send electricity in two directions in one consumer unit. I know we have the stickers and it's common practice but I didn't yet meet an electrician who wasn't surprised when he first heard that you simply feed into an MCB in the main CU.

I'm afraid this is unavoidable. The CB will always have current flowing in both directions.

I think installing on a seperate consumer unit is a good idea but it won't avoid the problems that you describe.

 

[Markc]

Firstly I'd like to apologise, I posted some misleading info, sorry!

MarkC you are completely correct. I always put inverters on RCD protected circuits a a matter of course, additional protection is becoming standard and that's how I work. I glanced through the DTI guide looking for confirmation that my methods were regulations rather than just my own practice and saw RCD and thought bingo. The Inverter doesn't need to be on an RCD protected circuit if the cables are surface mounted etc.

My preferred practice is to install a second DB cut into the main tails where I have an RCD main switch and a 16amp breaker. By doing this I don't need to go into an existing DB, many of which are old and ugly. Additionally it procides a clear and simple solution for customers like Brummygit who can then clamp an energy monitor onto the tails to the 'Consumer Unit' and if they want to another to the tails of the 'Generation Unit'.

Again it's a matter of personal preference but I think it's less than ideal to send electricity in two directions in one consumer unit. I know we have the stickers and it's common practice but I didn't yet meet an electrician who wasn't surprised when he first heard that you simply feed into an MCB in the main CU.

Given the cost cost of a PV system I think that if space permits that a separate generation DB is best practice and that's how I try to do my installs.

And no one can knock you for committing to better practice over minimum requirements (BS7671). On the RCD front if you are fitting a 30mA RCD on a TL transformer you will still need a Class B RCD to comply with BS7671.

 

[Markc]

Thanks for the suggestions and also advice from Mark C.

In answer to Mark C's points - I do not see a fault with the installation, and as far as I can tell it complies with BS7676 as there is a single externally conduited cable run to up my outside wall, then surface mounted cables inside my loft, and surface mount plastic trunking inside the meter cupboard. I'm interested in the different opinions around class B RCD requirement between Fronius and yourself and might ask the installers for clarification.

The problem with the monitor on the grid feed is that I also want to record the data via my PC and an internet server and the data I collect cannot go negative and therefore gives invalid results - sadly Google Power Meter and similar software can't switch a light on and see which way the readings change.

It looks like getting an electrician in to lift the board off the wall and clamp the cables as they enter the cavity using as many (or few) as needed. My monitor will automatically add 3 together when operating in 3 phase mode so this may well solve my problem. There should be space inside the cavity for the clamps as there isn't in the CU.

Thanks

I can defiantly confirm the internal RCMU on the Fronius TL inverters do not in any way form protection on the issues being raised here. Disregard the need to have a 30mA RCD on this system and no AC cable is embedded in the wall. This type of RCD will be the one as fitted to your existing consumer unit.

The Class B RCD will be a standalone unit located adjacent to the consumer unit in a majority of cases. This deceive prevents DC voltage being injected into the AC system i.e. your sockets and lights and grid network and so protects you and your family. This unit is a regulation and must be fitted to comply with BS7671. If it is not there it is a none compliance. Further to this it is also a regulation to earth bond the array. This is done in two ways and is dependent on the earthing arrangement of your property. If you have as TNCS also called PME system a earth electrode (Stake) must be driven into the ground and a 10mm green and yellow earth cable taken form the stake to the array on the roof. The second option is if TNCS or PME is NOT at your property and you have an alternative arrangement TNS or TT then the same size and colour earth cable is again taken from the array on the roof to the main earth terminal within your consumer unit. One way to check if this is done would be to look in your loft and a majority of the time this earth cable would take the same route as the AC cable.

All the above is only a requirement if using a transformerless inverter (TL). A TL is more efficient to standard transformered inverters due to less losses. As your system is a free-rent a roof design the installation company will obviously want to maximise their return to investment. By employing a TL inverter this is achieved HOWEVER the costs of such sundrie items such as the Class B RCD can be considerable considering their size. Nether the less it is a requirement and is for protection.

Our aims here is to provide constructive and honest advice and as an accredited installer feel it important to to post honest and correct advice. I am not claiming your system is none compliant but it may be worth a look and check. I am sure the installation company will be more than willing to give advice and if need be corrective action to comply. After all they have already moved the installation to a none RCD side.

Apologies for hijacking your thread and good luck with trying to achieve what you originally asked.

 

[BrummyGit]

Hi Ramjam - thanks for your contributions which are gratefully received. I would also have preferred to have the meter tails split and a second CU installed exactly as you describe and would have been willing to pay for it, but without fitting a larger meter box I can't see how it could be done. To be honest my existing 200mm tall CU could do with splitting into dual RCDs but I couldn't even fit one of the newer tall CUs in the box.

Hi Mark C - thank you. I am sure the installers would take seriously any installation issue from my experience so far. I know an earth spike was fitted and cabled up as far as my inverter, however I am not sure that they earthed the array itself unless the DC cables also carry earth. Additionally I need to check if a type B RCD has been fitted as I'm pretty sure it hasn't.

Both - I agree that a type A RCD would have been desirable, and was initially happy when my inverter was wired through the RCD side of my CU. But the Fronius IG TL simply won't work on a 30ma type A RCD as it needs 100ma instead.

 

[Worcester]

I had a long chat today with the devlopment team at CurrentCost (Current Cost - Reducing your energy bills so you can live a greener life) and explain the challenge with Solar PV - they are working on a solution ... so watch this space.

Soon you'll be able to upload the output from the three monitors to THEIR website, (it'll need the EnviR) and they don't believe that any changes need to be done. If they do it'll be the bridge and they said it would just need reprogamming (probably got linux on a chip) and they would offering free reprograming on a swap in / swap out basis.

I am working with them to produce a specific package for Solar Installations. We'll see how it goes.

 

[claypole]

BrummyGit, instead of taking the pv AC to an existing MCB, could you take it to the downstream end of the CU incomer, both the live and neutral coming directly off the bottom of the switch, or maybe squeeze a block in here so as to feed both pv L and N, and L to rcd + N to neutral bar. Then fit a sub main switch and appropriate mcb up by your meter. Your monitor clamp could then go under your existing CU cover, attached to the neutral wire link to the neutral bar. From here the only flow would be in 1 direction, to the house load, so you would effectively be able to monitor the house consumption. After negotiations with, and input from, my friendly spark that's exactly what we've done today, except that I have room for the submain adjacent to the CU. In this way the existing CU switch will still act as a single point of isolation.

 

[mantissa]

You've lost me there, any chance of a diagram?

My panels are being installed as we speak and I have just rumbled that my energy monitors will be almost useless now! I'd love to do be able to correct that, but without too much fuss. I'm not sure I follow your suggestion, but would love to be able to!

Thanks

 

[claypole]

I can try and get some pics tonight but in essence we simplified it without using a block. Used a sub main which took it's live and neutral from the bottom terminals of the mains switch on the CU. The sub main just has 1 x mcb for the solar. The monitor clamp then fits inside the CU clamped to the neutral link wire between the mains switch bottom terminal and the neutral bar that all the load neutrals are connected to. The only current that flows through this link is house load. Works a charm.
If you still need pics let me know.

 

[mantissa]

OK, thanks for the clarification. I think I've got it now.